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    Is PVC an acceptable vent material for flue gases? (122 Posts)

  • Tim McElwain Tim McElwain @ 9:07 PM
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    Is PVC an acceptable vent material for flue gases?

    An excellent article on this subject by Ron George in the May 2011 Plumbing Engineer Magazine. He supports with his findings many of the things i have posted here. Read the article if you can it will open your eyes to this dangerous practice.

    Ron is President of Plumb-Tech Design and Consulting Services LLC. He has served as chairman of the International Residential Plumbing and Mechanical Code Committee. Visit his e-,mail is [email protected] or phone 734-755-1908.
  • Tim McElwain Tim McElwain @ 9:19 PM
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    Here is the article, I hope it fits?

    Is PVC an acceptable vent material for flue gases?

    By Ron George,CPD,
    President, Ron George Design & Consulting Svcs.

    I recently inspected the mechanical systems in student housing at a Midwest university. The school had hundreds of apartments in numerous buildings with high efficiency water heaters that were installed more than 10 years ago. There were reported problems of not having enough hot water. I recently inspected the mechanical systems in student housing at a Midwest university. The school had hundreds of apartments in numerous buildings with high efficiency water heaters that were installed more than 10 years ago. There were reported problems of not having enough hot water.

    My inspection revealed a high efficiency water heater with purple/brownish PVC pipes and yellowish PVC flue pipe fittings. The flue pipes were obviously deformed from heat, and they were sagging. A maintenance man for the university said that some really bad pipes had come apart at the fittings and melted. This set off the carbon monoxide alarm and prompted a maintenance call. The water heater had scaled up due to minerals in the water supply; this caused the flue gas temperatures to rise, which created the noted problems.

    The pipe was Schedule 40 PVC pipe. Although the water heater installation manual we obtained recommended using PVC pipe as a flue material, PVC pipe manufacturers do not recommend this. I called the manufacturer of the PVC pipe in this case and asked the representative a few questions about using PVC pipe as a combustion flue for fuel gases. He was quite familiar with this issue and emailed me a link to the company’s technical manual, which discussed all of the physical and temperature limitations of the piping.

    He said that the company has had numerous complaints about PVC pipes used for venting flue gases, and that they always point out that they do not recommend this usage and that there is no listing for it in their manual. He has asked every major manufacturer of boilers and water heaters for data to support the recommendations in their literature for the use of PVC pipe for combustion flue materials but has not received any replies.

    This is concerning to me. Just because a manufacturer recommends using PVC does not mean that it is acceptable or safe. Just because PVC works in new installations does not mean that a condition cannot occur in which scale builds up over a short time in hard water areas and causes high flue gas temperatures. Most boiler and water heater manufacturers list other ways of venting with stainless steel, but they seem to always recommend the cheapest way in their literature, in an attempt to make the boiler seem more affordable to consumers.

    The piping manufacturer’s PVC pipe technical manual has the following information:

    Using Plastics for Combustion Gas Venting

    The piping manufacturer recommends that inquiries about the suitability of plastic piping systems for venting combustion gases should be directed to the manufacturer of the water or space heating equipment being installed.

    As stated in the International Code Council’s International Fuel Gas Code 503.4.1.1:
    Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions.

    Furthermore, several of the ASTM standards applicable to PVC plastic pipe and fittings that this company manufactures their pipe to include the following note: This standard specification for PVC pipe does not include requirements for pipe and fittings intended to be used to vent combustion gases.

    There is no standard referenced in any of the codes in the United States for a plastic flue vent for combustion flue gas piping, although many water heater and boiler manufacturers recommend this. There is a Canadian standard, ULC S636, but that standard has several flaws in that it allows flue gas temperatures that exceed the temperature limits of the pipe material manufacturers.

    The maximum temperatures listed in the ABS, PVC and CPVC pipe manufacturers’ technical literature are shown in the following table. Any temperatures above the rated temperature will allow the pipe to melt, sag and, possibly, collapse or pull apart. There are serious consequences with carbon monoxide asphyxiation and fire that cannot be ignored.

    Generally, for a new condensing water heater or boiler, the stack temperature will be about 20 degrees higher than the water temperature. The design and efficiency of the unit, along with several other factors, including water quality, will affect the stack temperature. If a water heater is set to store water at 140 F to minimize Legionella bacteria growth, the flue gas temperature will be about 160 F when the heater is new.

    As scale builds up and the heater efficiency falls off, the flue gas temperatures can easily increase to over 350 degrees F. Even if someone had their water heater set at 120 F, with scaling, the flue gas temperatures can rise well above 300 F. Boiler thermostats or burner controls are generally limited to 200 F, commercial water heater thermostats or burner controls to 180 F and residential water heater burner controls to 160 F, and all can overshoot by several degrees. As scale builds up on the heating surfaces, the scale insulates the flue gases from the hot water in the system, causing the flue gas temperatures to increase.

    As scale builds up and the heater efficiency falls off, the flue gas temperatures can easily increase to over 350 degrees F. Even if someone had their water heater set at 120 F, with scaling, the flue gas temperatures can rise well above 300 F. Boiler thermostats or burner controls are generally limited to 200 F, commercial water heater thermostats or burner controls to 180 F and residential water heater burner controls to 160 F, and all can overshoot by several degrees. As scale builds up on the heating surfaces, the scale insulates the flue gases from the hot water in the system, causing the flue gas temperatures to increase.

    Some boiler and water heater manufacturers offer stack or flue gas temperature gauges as a way to see whether the unit is scaling up and losing efficiency, which is helpful for monitoring the flue condition. A temperature sensor or probe with a high-limit control could be inserted into the flue at the flue connection to the boiler or water heater.

    This control would shut off the burner if the flue gas temperature exceeds the temperature rating of the flue pipe.

    A standard will be needed for plastic flue pipes that should include a temperature gauge and a high limit probe. Then PVC, CPVC and polypropylene flue gas piping can be safely used on high efficiency boilers and water heaters. This would be an answer to the dilemma of cost versus safety.

    Without a standard for proper use of these safety devices in combination with plastic flue gas piping or without the use of stainless steel flues, plastic flue materials can melt as flue gas temperatures rise. Not only is energy lost when this happens but flues can become blocked or disconnected, which can be a carbon monoxide or a fire danger.

    A family of four died in Aspen, Colorado, in 2008, of carbon monoxide poisoning from the failure of PVC plastic flue pipes on a condensing snow melting boiler system in a rental property. The plastic pipe manufacturer was not at fault, because they had published limitations on the use of their piping, and they had not recommended PVC piping for that application. The boiler manufacturer that recommended using PVC pipe as flue material was a target of the liability claim by surviving family members.

    I have heard arguments by many contractors that do not believe PVC flue venting for combustion gases is a problem, but I have seen melted and discolored piping in many of my investigations, so I know it is a problem. I also see the proliferation of recommendations from high efficiency, condensing boiler and water heater equipment manufacturers for the use of combustible and unlisted PVC piping products as corrosion resistant combustion flue venting.

    This approach seems to be a way to lessen the initial cost of installing a high efficiency boiler or water heater. High efficiency equipment will cost significantly more than less efficient models, so there seems to be a movement by manufacturers to promote these unlisted and, therefore, non-code-approved materials over code approved and listed stainless steel flues, which are corrosion resistant.

    This approach seems to be a way to lessen the initial cost of installing a high efficiency boiler or water heater. High efficiency equipment will cost significantly more than less efficient models, so there seems to be a movement by manufacturers to promote these unlisted and, therefore, non-code-approved materials over code approved and listed stainless steel flues, which are corrosion resistant.

    Some people argue that the mechanical code allows you to follow the manufacturer’s recommendations. The 2009 International Mechanical Code (IMC) has the following language:

    801.20 Plastic Vent Joints. Plastic pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions.

    Section 802 Vents

    802.1 General. All vent systems shall be listed and labeled.

    There is no listing for plastic piping for flue gas venting applications.

    The 2009 IMC also has the following language:

    Section 304 Installation

    304.2 Conflicts. Where conflicts between this code and the conditions of listing or the manufacturer’s installation instructions occur, the provisions of this code shall apply.

    Exception: Where a code provision is less restrictive than the conditions of the listing of the equipment or appliance or the manufacturer’s installation instructions, the conditions of the listing and the manufacturer’s installation instructions shall apply.

    There is a conflict between sections 801.20 and 802.1. The water heater manufacturer’s installation instructions conflict with the requirement in section 802.1 that requires all vent systems to be listed and labeled for the application. PVC pipe is not listed and labeled as a combustion flue pipe material, as noted in the piping manufacturer’s notes above, yet manufacturers of the water heaters and boilers seem to be avoiding the issue, and they continue to recommend the use of PVC flue venting in their installation instructions.

    Section 304.2 addresses conflicts. The code restriction requiring all flue materials to be listed and labeled for their intended purpose is more stringent language, so the more restrictive code requirement requiring listed and labeled flue pipe materials would apply. There is additional language in the International Fuel Gas Code.

    I have not seen any testing data or an independent test report from a boiler or water heater manufacturer that shows that PVC piping has been tested and approved for the conditions it will likely see in a water heating or boiler installation. Any testing should include the extreme conditions when scaling occurs and flue gas temps rise, near the end of the equipment’s service life.

    The Canadian standard, ULC S636, covers the design, construction and performance of gas venting systems intended for negative or positive pressure venting of gas-fired appliances producing flue gases having temperatures under the following:

    1. Class I venting systems are suitable for gas-fired appliances producing flue gas temperatures of more than 135 C (275 F) but not more than 245 C (473 F);

    2. Class II venting systems are suitable for gas-fired appliances producing flue gas temperatures of 135 C (275 F) or less;

    3. Class II venting systems are further classified into four temperature ratings as follows:
    (A) Up to and including 65 C (149 F)

    This temperature limit was intended to allow the use of PVC pipe for use as a flue gas material. The temperature limit for PVC pipe is 140 F, and the allowable temperature in the ULC S636 standard exceeds the temperature limits set by PVC pipe manufacturers.

    (B) Up to and including 90 C (190 F)

    This temperature limit was intended to allow the use of CPVC pipe for use as a flue gas material. The temperature in the pipe manufacturer technical data is 180 F. The ULC S636 standard allows the material to exceed the limit for CPVC piping by 10 degrees Fahrenheit.

    (C) Up to and including 110 C (230 F)

    This temperature limit was intended to allow the use of Polypropylene (PP) pipe for use as a flue gas material. There is currently one manufacturer listed to this standard, but the potential for the flue gases to exceed the 230 F is still there. A high-limit switch to shut off the boiler or water heater would be advisable.

    (D) Up to and including 135 C (275 F)

    I am not aware of any plastic pipe manufacturers that meet this sub-section of the standard. The potential for the flue gas temperatures to exceed the 230 F is still there. A high-limit switch to shut off the boiler or water heater would be advisable.

    It will be interesting to see which way the industry goes on this issue. There are forces pulling each way, and I believe that a significant change will be coming within the next few years. I hope the industry can develop a standard to allow low cost, high temperature plastic materials. I believe that we will see a few code changes on this topic in the next round of code hearings. The 2012 Code is nearing completion and should be available in 2011. The 2015 code cycle will begin in the not too distant future.

    Ron George is president of Plumb-Tech Design & Consulting Services. He has served as Chairman of the International Residential Plumbing & Mechanical Code Committee. To contact Ron, write him at [email protected]
  • Mark Eatherton Mark Eatherton @ 11:07 PM
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    I hate to say it, but....

    I've been using PVC for venting the high efficiency appliances for as long as they have been on this side of the pond. I regularly go by the first Munchkin job I did and observe and sample the PVC serving this neglected, high temperature (strictly DHW thru a HTP tank) application and other than exterior surface yellowing, I've not seen any degradation that would cause me concern.

    I also do work with a forensic engineering firm with 10 employees, and they are specialist in CO and fire, explosion and collapse, and I've asked them many times if they've ever seen a failure of PVC venting systems, and the answer is one (1) in all the hundreds of investigations they have performed, and that was on an appliance that was being run on LP without a conversion kit. He said it basically melted the first few inches of venting, and collapsed inside of the no hub connector.

    Now, with all due respect to Mr George, he sites the Aspen case. I am under the impression that the PVC joint was not glued, and came apart. Will using S.S. guarantee proper installation and fastening? I don't think so. Nothing will keep people form doing stupid things. No approved materials, no approved methods.

    With that said, how many Wallies have witnessed deformed or failed PVC piping on gas fired appliances?

    I'm just guessing here, but if it is proven that PVC does have the ability to withstand the operating temperatures/pressures in these new systems, the PVC manufacturers will line up and get their certifications, and start charging a premium for their product....

    As for high temperature flue gasses, the Knight has a sensor that limits the fire. If (and you know they are out there) someone neglects their appliance, and abuses it, the flue gas sensor will limit the burner, and the consumer will eventually complain about DHW or SH shortages.

    Just saying... Show me the evidence of failures, all standards set aside, for the time being, and I will join your band.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • TonyS TonyS @ 11:50 PM
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    I have replaced some

    of the first condensing furnaces that I installed because of failed exchangers after 20 years. The PVC outlasted the exchanger, so you might as well consider the steel exchanger unfit to. I did not reuse the PVC but I could have.
  • Jean-David Beyer Jean-David Beyer @ 7:22 AM
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    I am under the impression that the PVC joint was not glued

    I know for sure that most of the joints in my vent system were not glued. One reason why I have a new contractor. The joints were purple, though, and that was enough to fool the inspector, unfortuanately. I doubt the contractor was trying to save money on glue,  but it certainly can happen.

    It was like that for a year and a half, and I did not die, and my carbon monoxide detectors did not go off.

    I wonder how lucky I was.

    1.) The boiler, if properly adjusted, should put out only 60 ppm of carbon monoxide. I would not wish to breath that very long, but it would dilute fairly fast.

    2.) The pressure inside the vent is not very high, though I have not measured it.

    3.) If the vent did leak at the joints, the CO would leak into my garage, not directly into the house. The house is not perfectly sealed from the garage, but there is no door directly from the garage to the house.

    4.) I have three carbon monoxide detectors; two of the standard big box store type and one in my bedroom that is the high sensitivity type.

    5.) Of course, as soon as it was determined that the joints had not been glued, all that was replaced by my new contractor.
  • Ron George Ron George @ 9:51 PM
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    PVC Flue Pipe Failure - CO poisoning!

    I have been made aware of two PVC pipe fittings that cracked and caused carbon monoxide poisoning in a residence in the Pacific Northwest.  I visited the site and took photos of PVC pipe that was very brown and discolored within about 6 feet of the two  water heaters and two yellowish fittings that were cracked and completely seperated.  There were no expansion issues as the pipe was not restrained in any direction.  Testing the Flue gasses revealed flue gas temperatures were much higher than the system temperature and far in excess of the temperature rating for PVC pipe.  The water heaters were piped in series and both were set at 160 F.  The water heater manufacturer's literature reccomended the use of PVC pipe, even though the International Fuel Gas Code requires all flue pipe and fittings to be listed and labels for their application.  No PVC pipe and fittings are listed and labeled for use as Flue materials.  The water heater manufacturer's literature made no mention of system design limitations or temperature limitations for the Thermostat on the heater for systems using PVC flues.  The 160 degree water circulated through the heating coils for heating, and there was an ASSE 1017 mixing valve at the heaters to send tempered water to the plumbing system.  The PVC flue pipe seperation above a drywall ceiling, allowed carbon monoxide to vent into the house over several years and caused excessive mold and water damage.  The owner/occupant was a 40 yr old professional female who worked in a high paying position for a major national magazine.  She started developing a mysterious illnesses and symptoms and after a while was not able to climb the stairs in her home so she slept downstairs on a sofa.  She went to the doctors for the various illnesses and medical conditions over a several year period but no one suspected CO.  At one point she was so weak she could no longer work and she had to move to California to live with relatives.  She She continued with medical treatments in California for the mysterious illness which has left her disabled and unable to function.  She is on disability.  She decided to sell her home and the home inspector found significant water damage.  When a contractor opened up the drywall he found two completely seperated PVC flues pumping CO and moisture into the home.  The plumbing contractor saw the broken PVC pipes and called the homeowner not knowing her condition and asked if she had experienced any Carbon Monoxide Symptoms like:
    •Headache, Dizziness, Nausea, Flu-like symptoms, fatigue, Shortness of breath upon exertion, Impaired judgment, Chest pain, Confusion, Depression, Hallucinations, Agitation, Vomiting, Abdominal pain, Drowsiness, Visual changes, Fainting, Seizures, Memory and walking problems.
    These were many of the symptoms she had been experiencing.  The CO levels were higher than the EPA reccomendations for one 8 hour exposre per year.  She lived in this home year round with CO levels recorded in the home higher than the EPA allowable levels.   I also found it interesting that the typical CO alarm levels are much higher than the EPA maximum exposure levels.  you are more likely to experience sysmptoms prior to the alarm going off.  Stay Tuned as the investigation continues.
  • Mark Eatherton Mark Eatherton @ 8:58 AM
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    This woman is lucky to be alive...

    Just guessing here because I have no experience with this particular product, but if it were drawing combustion air from within the same space as the appliances location, she'd have been dead a long time ago. The tendency for CO generation from flue products leaking into the combustion zone is compounded. Flame doesn't burn well in the presence of CO2, and the CO levels increase significantly, and people suffer the consequences.

    I'm thinking that the appliance is sealed combustion, drawing the air for combustion from the outside. In other words, she was being exposed to the CO that is typically found in the flue gas stream, and if properly adjusted, that concentration should be fairly low. Still not a good idea to expose yourself to the products of combustion, but not as bad as a compounded issue.

    It also sounds as though this is a great example of something that SHOULDN'T be done in the field in the first place. I suspect that this lady was also exposed to a lot of water borne bacteria that become air borne while in the shower. I just received my IAPMO disc of proposed code changes, and I HOPE that I find that they have banned the use of "Open Combination DHW/ Space Heating Systems", but am not holding my breath...

    Edgar Allen Poe is rumored to have been suffering from the effects of long term low level CO exposure... I hope she recovers.

    I think this thread may be setting a record for the most views as well.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
    This post was edited by an admin on April 9, 2012 8:59 AM.
  • Jean-David Beyer Jean-David Beyer @ 10:04 PM
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    Metered my PVC vent pipe today.

    I am not a professional, but I am curious about these things.

    Today I had just run my dishwasher and took my portable IR meter to see what my white 3" PVC exhaust vent pipe measured.

    The boiler (W-M Ultra 3) was trying to produce 170F water to send to my indirect hot water heater. The water was a little over 70F when it started (warm out, and no heat was required for the house since midnight, if not before). The indirect's aquastat was set a little over 120F.

    The vent comes out of the top of the boiler, goes up about 15", goes through a 45 degree elbow, a very short piece of straight pipe, then another 45 degree elbow, and straight up near the ceiling, where it goes through a 90 degree elbow and on its way.

    As this pipe was warming up, I measured around to find the hottest spot. This proved to be at the end of the second 45 degree elbow, on the outside of the curve where the exhaust was probably hitting it.

    I watched the IR thermometer and glanced at the supply and return temperatures going to and from the indirect. The supply never made it to 175F because the aquastat was satisfied at about 170F supply. The return was about 150F at that point. When that happened, the outside temperature of the PVC vent pipe was 111F. This experiment took between 5 and 10 minutes, but I did not time it.

    Comments by experts welcomed.
  • Ron George Ron George @ 9:58 PM
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    Flue Temps recorded

    I recorded the flue temperatures inside a PVC Pipe a few inches from the water heater flue discharge.  I did this by drilling a small hole in the PVC pipe and inserting a temperature probe.  The internal temperature reached 175 F.  The system was set at 160 F.  The Maximum PVC temperature is listed as 140 - 149 F depending on which literature you look at.  In either case 175 is too hot for PVC. 
  • Paul Rohrs Paul Rohrs @ 8:48 AM
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    PVC Temperature

    You "recorded the flue temperatures".  Great, 175°F temp of flue byproducts.  Understood.    What were the temperatures of the PVC wall?


  • Ron George Ron George @ 2:40 PM
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    PVC wall temps

    The infrared gun read 182.3 F on the exterior of the black plastic housing connecting to the PVC pipe the exterior of the PVC pipe just above the water heater was 163 F. The flue gasses inside the PVC pipe were measured at 175 F.  The internal flue gas temperatures were measured a couple of feet downstream of where air inlets pulled in room air to mix with the flue gasses and downstream of the fan.  The actual flue gas temperatures were much higher until they fully mixed with the room air it appears there are areas of extremely high flue gas temperatures near the heater as evidensed by the significant discoloration and cracking and separation of the PVC flue pipe fittings.   Please show me any documentation by a boiler manufacturer or a water heater manufacturer or a Furnace manufacturer that shows where they have tested and certified PVC to be used as a flue gas material and provided a guarantee that the flue gas temperature will never exceed 140 F.   The tests and the documentation simply does not exist.  There is no way anyone can guarantee the flue gas temperatures will not exceed 140 F in an extreme situation.  (Scaled up heating surface in a boiler or water heater or when there is a dirty air filter in a furnace.)  With metal flues these conditions lead to wasted energy.  in PVC flue situations it can lead to flue failure and carbon monoxide poisoning!
  • Chris Chris @ 10:25 PM
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    How Its Done

    Here is the trick of the trade and how the mfgs get away with it. It's very simple and in every installation manual.

    They list that PVC can be used if it meets ASTDM 1785. 1785 clearly states that PVC can be used in temps up to 140 degrees. But nobody reads the stupid manuals. They will also see the other means of venting Z-Vent or a vent pipe that meets ULCS-636. They have covered there butts and you the installer now holds the bag. Installing PVC as a vent material exceeds the standard so you are suppose to go the next recommended vent pipe in the manual!!!

    Problem is most contractors couldn't tell you what ASTDM 1785 even says. They just assume the pipe can be used because it is in the manual.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer Jean-David Beyer @ 7:05 AM
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    PVC can be used in temps up to 140 degrees.

    What I measured was the temperature at the outside of the PVC vent pipe. It seems to me that it would probably be better to measure the inside wall of the vent pipe, other than the technical difficulties of doing so.

    Now, if I never have my boiler serviced, then the exhaust temperature wil lgo up as the crud builds up in the heat exchanger. I do get it serviced, so this should help.

    My boiler has an exhaust temperature probe (actually two probes in one for redundancy). This dual sensor is in the vent pipe immediately as it comes out the bottom of the heat exchanger. Inside the boiler, the vent pipe seems to be stainless and it exits the top of the boiler, perhaps 2 feet up, where it changes over to PVC. So the exhaust as it hits the PVC is probably a little less than when it exits the boiler. If the two flue sensors are more than 10F apart, the boiler will shut down until the two sensors are within 10F. If the flue temperature exceeds 210F, it will shut down for 1.5 minutes if the temperature gets back down. If flue temperature gets up to 220F, it will shut down and will not restart until it is manually reset. This may prevent immediate problems, but it sure will not keep the PVC under 140F.

    I see that vent pipe every day, so I would probably notice a color change, other than a very slight one. I wonder if a color change would be enough to determine when the pipe should be changed.
  • pipe4zen pipe4zen @ 7:30 AM
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    temperature and pressure

    is how they gey around it.

    The PVC manufacturer is testing for a maximum temperature while at a given pressure.

    A flue pipe is not under pressure, there is and open end to the outside(we hope). Pex is rated the same way also, the standard lists several max temp/pressure ratings.

    One thing I do is size of pipe correctly, if a water heater is using 2" PVC but is vented long distances,including elbows, then an upsize should be done, so static pressure drop at the equipment is not high causing the high temps to linger around at the water heater.
  • Jean-David Beyer Jean-David Beyer @ 8:02 AM
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    vent pipe size

    My boiler allows 2-inch or three-inch PVC for the distance and number of elbows in there. My installing contractor used 3-inch everywhere.

    (Similarly with the copper and iron piping, where he used 1 1/4 inch where the manufacturer specified at least one-inch.)
  • TonyS TonyS @ 8:58 AM
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    The article seems well written but fails to deliver some important information. High efficiency water heaters means nothing to most professionals. "Everything" today is high efficiency, so it has lost any real meaning. He should have at least broke it down into Condensing or Non-condensing and a little more info on the units would help.
  • Mark Eatherton Mark Eatherton @ 10:07 AM
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    I agree with Tony....

    Although Mr George is very well educated on what the code says, it would appear that he has little working knowledge of what is actually going on out in the field. I think most modcon manufacturers are well ahead of his thoughts as it pertains to protecting the flue gas disposal systems, and the possibility of a fouled heat exchanger...

    Having not worked on every modcon that is out there, I can't vouch for all of them, but the experience I have with Lochinvar goes in a different direction than the statements in his article.

    Now, if it were Plex Vent, I am certain that there would be a LOT more responses about seeing failures in the field. I know every one that I inspected was obviously cracking, crazing, checking and leaking. I've not seen any of that in the PVC venting systems I see on a regular basis.

    I should probably ask the respondents to tell us whether it was a high efficiency modcon or just a forced draft water heater/furnace. Big difference in the operation of the two...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • hot rod hot rod @ 10:44 AM
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    If your PVC vent pipe

    went from bright white to "brittle beige" in a couple years time I think you might wonder. This is one of many in a multi unit building. As I understand it the temperatures were cranked and the building was still under-heating.

    So the concept of a high temperature flue gas condition, possibly scaled boiler which is not un-common in aluminum block boilers that may not have appropriate water or fluid quality. It could be a perfect storm brewing.

    The product being used to vent by products of combustion should be listed to that purpose or we my be going down the same road, or rockier road than we did with the hight temperature plastic vent systems. Only that was designed for venting.

  • Jean-David Beyer Jean-David Beyer @ 11:54 AM
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    Discolored PVC piping.

    In that picture, both PVC pipes are discolored, although the exhaust one is more discolored than the air intake one.

    How do you  account for the discoloring of the air intake pipe? Because it would be difficult for me to believe that the air intake was anywhere near 140F. And what is the cause of the lighter colored stripe a few inches below the red arrow?

    Were these two pipes about to be replaced, or did you decide they were OK for continued service?
  • Ron George Ron George @ 4:55 PM
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    Only one pipe is discolored

    The only PVC pipes in the above photo are uninsulated and connecting to the top of the appliance.  It appears JDB was comparing the color of the water pipe insulation jacket color to the color of the PVC pipes.  The insulation jacket on the adjacent water piping is bright white compared to an off white for the PVC.  There does not appear to be any discoloration of the combustion air inlet PVC pipe to me.  But there is a definate difference in color between the inlet PVC pipe and the outlet PVC pipe.  The heat from the combustion gasses is definately affecting the flue gas exhaust pipe different than the combustion air inlet pipe.  As for the photo below it shows a similar situation. If the discoloration was from car fumes as suggested below, I would think both pipes would be discolored the same.
    This post was edited by an admin on June 5, 2011 5:19 PM.
  • Mark Eatherton Mark Eatherton @ 10:03 AM
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    Been there, seen that...

    Inspect it on a regular basis for any major changes, and have seen none.

    This system is doing only DHW thru a HTP tank, from a HTP Munchkin. Essentially running at 180 degrees F all the time.

    Note that the discoloration is ON the exterior of the pipe, and that immediately under this surface, there is NO discoloration.

    This is also located in a downtown setting that has a LOT of automobile pollution in the air. Have not seen this in any of the other appliances I have installed.

    No exterior signs of embrittlement, checking, cracking or crazing.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Chris Chris @ 12:49 PM
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    Contractor Responsibility

    In the end are we not talking about responsibility to educate your customer and allow them the choice of what vent material to use based on your recommendation.  Charlotte clearly states PVC is not rated above 140 degrees. The mfg installation manuals give you several ways to vent and reference standards. Is it again not the contractors responsibility to know what the standards mean.

    If you were on the stand and I was the lawyer, the first question out of my mouth would be what does ASTM1785 mean? Next question, does the mfg of PVC state in it's techincal data that PVC is rated to 140 degree temperature? The third, did you check the standards of the other vent options as described in the mfg installation manul. The fourth, did you discuss each vent option with the plantiff and bring it to their attention that the heating appliance would be venting flue gases hotter then 140 degrees. The 5th, Why did you choose not to install the other venting products that were rated for flue gas temperatures the heating appliance would be producting?

    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on May 13, 2011 12:50 PM.
  • Jean-David Beyer Jean-David Beyer @ 1:21 PM
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    Educating the customer.

    "In the end are we not talking about responsibility to educate your
    customer and allow them the choice of what vent material to use based on
    your recommendation."

    Since I am a customer, not a contractor, I have an inclination to agree with you.

    Had my contractor explained the difference, both technical, between CSST and black pipe for my gas, perhaps I would have selected black pipe even if it cost more. Similarly, had he discussed the difference between appropriate stainless venting and PVC, CPVC, polypropylen, or whatever, who knows what I would pick? But if I picked it, would the liability then fall on me? After all, he is the one with the license. If I insist he violate the code, and put it in writing, does that get him off the hook? IMAO, he should refuse and walk away.

    But where do the lines get drawn? Should my contractor have told me about legionella and the cost of running my indirect 20F hotter and the cost of a suitable mixing valve as against the cost of hospital and medical bills? I suppose so. But at some point is it going too far? Should we discuss the relative merits of a Caleffi mixing valve vs one from Honeywell or Watts? At some point, pretty close to here, he will say I should do it myself. I do not want to be unreasonable about this.

    I think I am atypical as a customer though. People I know could not care less about their heating systems. One did not even know where it was in her condo (a closet right off the living room). I wonder if she ever has it serviced? It is forced hot air, gas fired. Does she even change the air filters? Some buy a heating system like they buy a microwave oven: size, color, price. They do not want to know about, nor make, any of the decisions: that is what the contractor is for.

    As I have said before: I am really glad I am not a contractor and have to deal with customers.
  • Chris Chris @ 1:48 PM
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    In the Case

    Of venting. Your telling them why your not using PVC and recommending one of the other vent methods that are availble to you.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer Jean-David Beyer @ 2:28 PM
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    In the Case Of venting

    Of course, I happen to agree with you.

    And incidentally, I think you have solved a problem in educating the consumer and having him make the decisions. You do not have the customer make the decision. You make it and explain why: because in your professional experience the alternatives are not safe enough to stake your reputation on them. Now if the customer insists on buying by price on a detail like that, then I hope you make enough on your business that you can afford to lose that customer.

    If the customer has real money problems, you can discuss conventional boilers and mod-con boilers, pointing up the issue of up-front costs vs. continuing operating costs, and let the customer make that decision.

    In my case, I would have gone for black iron gas pipe vs. CSST, for example, but I was not asked if I had a choice or not.

    But so many of these should be really easy decisions. It looks to me that stainless vent pipe is about 10x more than PVC. Stated that way, it looks non-competitive, but when you figure it is only 4% of the cost of my boiler replacement (about the cost of the permits for the job), it is not unreasonable at all.
  • Tim McElwain Tim McElwain @ 7:56 PM
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    I have asked

    Ron George to join the discussion here to defend his finding's and perhaps expand on some points made by those posting here.

    I find this a critical concern for a number of reasons which I have expressed in the past including my findings of breakdown of chlorides and contaminating the combustion side of some of this high end equipment.

    I hope he joins us and let us try to be civil in our discussion.
  • Jean-David Beyer Jean-David Beyer @ 9:26 PM
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    Than you.

    I think that is a very good idea.

    The main thing that comes to my mind is that he seems to be thinking about domestic hot water heaters, and not necessarily condensing boilers. There seem to be some condensing hot water heaters (if I am not mistaken), but I do not know their efficiency as shown by their exhaust gas temperatures.

    It seems to me that with a condensing boiler, which would normally be run as a closed system, the chances of getting sediment on the water side of a heat exchanger would be fairly small. On the fire side, deposits should be easily detected and removed during annual mainitenance. I saw that done with mine, but it was only about a year old at the time, and it seemed pretty easy. If it were skipped for a few seasons, the stuff might be more difficult to remove. According to the regional rep from the boiler company, you should even be able to detect the need for cleaning by examining the exhaust gas temperature that can be obtained by diddling the buttons on the control panel. The exhaust temperature should be no more than 54F above the return water temperature. Of course different boilers would have different numbers. If I were putting 190F water into the indirect, that implies that it would be within spec. to get 244F exhaust temperature which would be a lot over the PVC pipe rating. I suppose the thing to do is keep an eye on the pipe and when it starts to turn yellow, to repalce it with AL29-4C. I suppose I can keep the PVC for the air supply.

    I see no reason not to be polite. Rudeness makes it difficult for minds to meet., and in the last analysis, I assume we would all like as close to a definitive answer to this as we can get.
  • Mark Eatherton Mark Eatherton @ 10:08 AM
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    I welcome his participation....

    and as usual, we are ALWAYS open and friendly here at The Wall.

    Maybe we can ask him why it is that combustion testing of all fired appliances is not in the national codes...

    Education and progress is good.

    BTW, I have come up with a solution for the chlorides leaching out of the venting systems and rolling back to the boilers, but would prefer to not dilute this topic...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Ron George Ron George @ 8:59 PM
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    Ron George's Reply.

    I appreciate all the comments.  I read the article as pasted above and I see there were several paragraphs that were copied in twice.  But the message is there.   I understand there many different dynamics in this issue.  The piping manufacturers, the condensing equipment manufacturers, the contractors etc.  The contractors have the fear that if they use something other than the cheapest material they may not be the low bidder.  PVC material is only a choice because the manufacturers have offered it as a choice.  PVC may not melt or sag in most installations, if the flue gas temperatures are kept close to the 140 degree limit and as long as the exposure time and the temperature difference are minimal.  Currently if a system is undersized and there is a hard water situation the flue gas temperature can rise significantly over time.  The piping will eventually fail in extreme situations.  As I explained the University staff removed and replaced the PVC flue piping in extreme cases without notifyng the manufacturer or calling an outside contractor.  Not all cases get reported. Even if they did report them, the manufacturers would not be willing to share these failures.  The University does not even want the noteriety.
    I want to just point out a few facts that if these were presented to a jury it might not bode well for manufacturer's selling equipment and recommending PVC venting or contractors installing PVC venting which clearly violates the codes and the standard for the product. 
    Here are a few points to note:
    1. The code requires all flues to be listed and labeled for the intended purpose. There is no such listing for PVC pipe used as combustion gas flues in the US:

    2. the piping manufacturers have the following temperature limits for the following plastic piping systems: 
    ABS Schedule 40                            160 ° F
    PVC Schedule 40                             140° F
    CPVC Copper Tube Size                   180° F
    CPVC Scheule 80                             200° F

    3. For those of you that do not have a copy of the ASTM Standard, ASTM D1785 standard applicable to PVC plastic pipe and fittings includes: the following note:"This standard specification for PVC pipe does not include requirements for pipe and fittings intended to be used to vent combustion gases".

    4. To those of you who wondered if I understand the difference between high efficiency and condensing,  They are the same in this case high efficiency boilers and water heaters are condensing appliances.  Thus they must use stainless steel (s/s) flues to prevent corrosion from condensing flue gasses. Manufacturers have are now recommending PVC as a less expensive alternative to S/S yet PVC is not listed for this application.

    5. To the person who wondered if this is only a water heater problem; In a closed boiler system you always have a make-up water connection.  In some cases if you have a leaky seal on a circulator or any other leak in the system make-up water is introduced.  If the water is neutral PH there is not much scaling, but if the water is hard (full of minerals) the minerals will preciptate out on the heating surface of the boiler causing a loss in efficiency.  The loss in efficiency = a rise in flue gas temperature.  This is when there can be problems.  I have seen many well maintained and properly installed systems work fine.  It is usually only when there is a design problem or installation problem that the high temperature flue gas is an issue.  A design problem is having a boiler water temperature of 200 degrees Fahrenheit.  The flue gas must be hotter than the water temperature!  In this case the flue gas temperature at best would be about 220 F.  Heating and hydronic system do not work as well when the heat transfer fluid temperature is lowered to 120 to 140 degrees F.  Many tmes the heating coils are designed for higher temperatures.  This is a common problem.  I am not sure if it is much of a problem for a gas fired furnace unless the filters are not cleaned regularly and the airflow drops off.  In that case it could also be a problem.

    6. I am seeing a proliferation of water heaters with a heating coil for heating hot water supplied to a fan coil unit in a residential unit.  I have also seen water heaters used without heat exchangers providing domestic hot water into heating coils.  A water heater is an open system and is a disaster waiting to happen in this situation with a PVC vent.  In the University installation mentioned above, there were 4 bedroom apartments with four students assigned to each apartment with a 48 gallon water heater with a heating coil in and a small circulator serving a fan coil unit.  It was serving four college students on cold winter mornings with showers, shaving, breakfast, dishwashing , clotheswashing and the heating load for the fan coil unit.  The burner in the water heater was working overtime without the winter temperature in the northern climate near zero for weeks at a time.  We found that the worst case flues were on units that were on top floors where there was a greater heating load.  I do not recommend combined heating hot water and domestic hot water heating systems for many reasons that are worthy of a full magzine article.
    7. As for using an infrared thermometer on the outside of the plastic flue pipe.  That will not give you the actual flue gas temperatures.  In the test it was mentioned the heat was not on for long.  In a newer installation or an installation with good water quality the temperature may not get too high.  When the burner is overworked because of being undersizing or overloaded, coupled with scale on the water side of the heating surface it causes the burner to stay on much longer and there is a loss of heat transfer into the water which causes the flue gas temperatures to rise.  This condition causes long cyles of high temperature flue gasses. 

    8.F.Y.I.  I have recently, since writing the article, and before the publication, I applied for a patent (pending) for a temperature sensor in the flue outlet of a boiler or water heater to sense excess temperatures and shut off the burner to prevent damage to PVC flue pipes. The controls allow intermittent operation to prevent freze-ups and it sounds an alarm to alert the homeowner of a problem. With this technology, Boiler and water heater manufacturers can utilize plastic vent pipes without worries of overheating.

    9. It goes without saying that installing a water softener in hard water areas is vitally important.

    10. As contractors and manufacturers you have an obligation to follow the code which as I read it does not permit plastic flues because they are not listed for that purpose.  If a manufacturer utilizes a temperature sensor to sense the outlet flue temperature they can propose a code change to allow an exception for plastic piping meeting a standard if they have a temperature sensor and burner controls to limit flue gas temperatuers.    There is an obligation to provide a safe system for the customer.  Even if the custmer elects to choose someone else to try and install it consider yourself off the hook if there is a problem.  I suspect it won't be long before the inspector organizations become aware of this issue and stop allowing PVC plastic flue pipes. Stainless steel flue pipes are available and other types of high temperature plastic materials are available (ABS, CPVC & Polypropylene) but there is not a product standard developed specifically for plastic flue gas pipe applications yet.  

    This post was edited by an admin on June 5, 2011 5:09 PM.
  • Tim McElwain Tim McElwain @ 9:21 PM
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    Thanks Ron for

    coming to the Forum here and answering the questions posed. I will take some time tomorrow to digest all this and I am sure some who typically post here will have some questions.

    We welcome you here by the way as there are often code questions that arise so if your valuable time permits stop by and visit us anytime.
  • Mark Eatherton Mark Eatherton @ 9:17 AM
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    Solutions to the problems....

    Regarding DHW system sliming up, how about the REQUIRED use of an electronic water conditioner. No chance of lime scale accumulation with these devices, and hence, no excessive flue gas temperatures.

    As for the control to watch the flue gas temperatures, the SIT controllers that are on many modcon appliances already have a flame suppression circuit if the flue gasses get too hot.

    As for closed loop heating systems, to the best of my knowledge, there are NO "requirements" for a solid connection to the potable water system. A good tight system should not require continuous make up. No leak is a good leak, and all leaks need to be taken care of immediately. I have not made a solid connection to the make up water on my heating system (except commercial applications) for the last 10 years. I cover this fact with a low water cut off wired in series with a low pressure cut off. If there is a leak on one of my systems, my insurance company (and ME) want to know about sooner, rather then never or too late. Numerous mechanical inspectors have reviewed my methodology (do a site search here for the term PIG) and have approved it, and have stated that it should be a code requirement.

    As for the use of non approved PVC for venting, or any plastic for that matter (ABS, PVC, CPVC) why not require full and complete support for all horizontal lengths (angle iron) of plastic tubing exposed to temperatures in excess of 140 degrees F. Remember also, as others have pointed out, that the initial testing and approval of PVC was with the weight of water and pressure being inside o the pipe. In the field application of the plastic products as venting products, they are NOT filled with water, and they are NOT being exposed to internal pressure of more than hundredths of an inch WC.

    This is America. We CAN figure it out. We need to establish a standard for plastic flue pipes, and we need to do it YESTERDAY...

    EDIT: One last thing that I've mentioned before that NEEDS to be instituted NOW, the required combustion flue gas analysis, and a follow up test every year or two. This will not only save energy, but will also save LIVES, at a minimal cost to the end user.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
    This post was edited by an admin on June 2, 2011 9:23 AM.
  • Ron George Ron George @ 9:59 AM
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    Good Points Mark

    One solution as you pointed out would be to requiring water treatment, but probably only in cases where there is hard water.  The threshold of hard water needs to be defined.  However the water in some areas may change in quality at different times of the year.
    As for the high temp limit on the boilers, water heaters, I'm not sure if all equipment has that technology.  In fact most of the tempeature sensors cut out at much higher temperatures. The temperature limit for each flue material would need to be mandatory then various types of plastic flue pipe materials could possibly be used with corresponding standard for the flue pipes.  I would be worried that PVC with a temp limit of 140 F would mean the operating temperature of the system would be about 120 F (about 20 degrees below the max temperature limit of the piping.  At 120 F the heating capacity of the system is less.  Most hydronic systems work better with temperatures closer to 200 F.  Many heat exchangers/coils are designed for heating hot water temperatures well in excess of 120 F.   

    This post was edited by an admin on June 5, 2011 5:12 PM.
  • Mark Eatherton Mark Eatherton @ 9:51 AM
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    Common culpability...

    Chris, you obviously (now) have a dog in this fight (poly propylene venting systems available now), but prior to that, your and your contractors choices were limited to the PVC or SS categories.

    What did you USE to recommend to your contractors? Got any PVC venting systems floating around in your closet? I realize that the majority of your systems were Viessmann, and understand their reasons for not allowing PVC, but I also know that you deal in other systems that DO allow the use of PVC. Did you only sell SS pipe for THOSE applications? Did you make the contractors who purchased PVC for venting those systems sign a release of liability form?

    I have nothing BUT pvc floating around in my closet, and I have had Z E R O issues, and in some cases, I know it is being seriously abused.

    It may not make it right, but I think that the industry needs to fall back and review the application and see if there is an acceptable niche market. Remember, the temperature / pressure ratings that were developed assumed the use of pressurized water. These venting systems are NOT seeing significant operating pressures, hence the tube may be more forgiving under these conditions.

    Don't get me wrong. I am all for safe operation of gas fired appliances. I just think this is a witch hunt that is really unnecessary...

    To borrow a line from a group (water heater manufacturers) that Dave Yates and I once had a long and arduous battle with, "Show me the bodies!"

    This stuff has been in service for well over 1/4 of a century. Why, all of a sudden, is it an issue now?

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Dave Yates (GrandPAH) Dave Yates (GrandPAH) @ 1:02 PM
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    You had to go there!?! That phrase still raises my BP(G). I too must confess I've found the PVC issues to be unwarranted from an anecdotal personal experience level. The worst case for us was a supply house telling us it was OK to vent what turned out to be an 80+ furnace with PVC. Seasonal service revealed yellowed & discolored PVC within the first few feet - badly abused PVC temp-wise. Lesson learned: don't let a supply house counter dude tell you what's correct!

    However, not one single PVC install on a 90+ furnace, modcon boiler, power-vent, or DV water heater has shown any evidence of any looming danger & we're now past the 20-year mark. I've encountered a few foam-core PVC exhaust vent installations & recently replaced one because we were replacing the modcon installed by another firm. I was pretty surprised to find it appeared to be in perfect condition after so many year of service in a system not utilizing outdoor reset that ran at much higher temps than required (following analysis and adding outdoor reset).

    The lone issues I've encountered were all a result of a faulty installation and exceeding the manufacturers' specifications.
  • Chris Chris @ 5:04 PM
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    The Closet

    I would be lying if I said I never sold it as a vent material. Back in the day when the brain began its hunger for knowledge never paid any attention to it. Mfg said is was ok. The funny thing is that in all the classes you never heard them once define ASTM 1785 and state that you should be using another vent method when stack temps exceed 140 degrees. Never one did you hear that PVC was not rated above 140 degrees. Now every class I participate in those are the questions I ask. So me the testing data. Seen plenty of sagging and as you have shown "brown" vent pipe out there.

    My stake in poly prop has nothing to do with Viessmann. We sell Triangle, Alpine, PureFire and others. If my hand is in the trigger of the gun then you getting quoted PolyProp and the reason why. You want the PVC that's up to you. I gave you the choice and my reason. I think contractors are fools for not using it from a sales aspect (money in your pocket). Willing to bet informing the customer you are using a tested vent system over your competition with the reason why closes a sale or two. We actually close Viessmann sales in cases just for that reason. Consumers today are more in tuned to the mechanical aspect of their homes then in the past.

    Poly Prop is a listed and tested vent system and offered at a reasonable price. We cannot talk price so not being able to share a cost comparision between 2", 3" or 4" PVC is a little disadvantage in proving the cost point.

    Could you please show me the deaths from "Plex Vent." I still have guys coming across it in the field and its recall goes back to 1998. Yes we all know it is not safe. The mfgs were smart enough to get together and stopped a potential problem before it happened. Why, because another mfg was holding the money bag not them. In the case of PVC the money bag would be in all their hands since the PVC mfgs have put its use in their hands.

    I'm going to Triangle on Thursday and the questions about venting PVC are on on my pad to ask.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • pipe4zen pipe4zen @ 6:48 PM
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    ASTM 1785

    Is a testing standard for PVC used for hot and cold water pressure systems. It's rates pvc that at a given temperature and pressure relationship. Any temperature over 73 F has a correction factor multiplier for pressure limitations, but temperature cannot exceed 140 F under pressure.

    ASTM 1785 has no authority for combustion flue gases. Just as ASTM 2665 would have no substance also (PVC used for DWV). You keep mentioning this standard , and as you know there is no seperate testing standard as of yet for PVC and combustion flue gas , nationwide.

    As long as equipment manufacturer's approve of it, then installer is covered , under law, if proving that it was installed correctly according to equipment specifications.

    If PVC piping was a problem, then you would think that the PVC cases that just about all of them have would be a problem, not to mention also, plastic condesate traps, pvc coated wiring running throughout the equipment , etc. But then it probably would not be a 0 clearance unit either.
  • Chris Chris @ 10:01 PM
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    I Keep Mentioning

    The standard because that is what is listed in all the installation manuals. I know about the correction factors I have them. Those correction factors also clearly show that PVC is not rated above 140 degrees whether at 1psi or 100 psi.
    To me that means, if you know your venting will see more then 140 degree stack temp don't use it. Move on to the next vent method provided in the manual.

    Is everyone so caught up in the cost of not using PVC? PolyProp which is clearly tested and stamped as a vent system for flue gas temps up to 230 degrees is not that much more then PVC. Its a heck of alot less expensive the Stainless. Ask your next customer which they would want in your next estimate. A vent pipe that is not tested for xx dollars or a vent pipe that is tested for xx dollars. We are talking about between a Mr Jackson and a Mr Franklin depending on the installation.
    If the pros stepped up to the plate and began offering it to their customers you would be surprised by the choice of your customer. They will take the vent system all day long. Why do we offer our customers the Alpha's, Wilo's, Taco VDT's, Zone Sentrys and all the other system side components as options but leave out offering a tested, labled and approved vent system?

    How many of you have offered your customer an alternative to PVC for venting?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • pipe4zen pipe4zen @ 7:33 AM
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    That's fine , if a wholesaler, or contractor wants to offer an upgrade to a different venting product. There are dozens of upgrades that can be offered as well, "L" is better than "M" copper, but I'm not going to imply there is a safety concern.

    But there currently there is no code violation , state or national, about using PVC sch. 40 pipe for equipment venting. There is no safety issue either, a properly installed and supported pipe. It will not melt or sag.

    The manufacturer lists ASTM 1785 , because they want you to use that type of pipe , not PVC cellular foam core, not ABS, not thin wall, because they don't have that ASTM.

    The 140F is a limitation for pressure installs, even at 1psi. A vent system has 0 psi. My only wish is that a national standard be given , no matter the outcome, and all installs then comply. Until then, current installs are safely and legally in compliance.

    So I agree with you, but also disagree with you.
    This post was edited by an admin on May 15, 2011 7:35 AM.
  • Chris Chris @ 8:21 AM
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    I Also Agree With You

    That there is no  violation based on code and that there needs to be a standard. I think Canada has given us that path and it should be adopted here.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Ron George Ron George @ 9:16 PM
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    Code Conflicts

    As the former chairman of a mechanical and plumbing code committee for one of the model codes, I would have the following intrepretation if I was asked.  When there is a code conflict such as the code conflict where the code requires all flue venting products to be listed and labeled for that application vs the manufacturer recommending PVC flues, The code must be followed.  There is an exception in the code that allows the manufacturers' instructions to be followed if the manufacturers' instruction are more stringent.  The manufaccturers instructions allowing PVC flue pipes is LESS stringent that the requirement for listed and labeled flue pipe materials.  Therefore, in my opinion PVC flue pipes are not allowed by code.
  • Charlie from wmass Charlie from wmass @ 11:01 PM
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    I am simply sitting on the side line

    with this discussion. I am just thinking of all the exhaust pipes that may need changed and who will the tab land with? If the use of PVC is determined to be dangerous on systems not running at proper radiant temperatures will the manufacturers of the boilers be held to task or will the home owner get the bill, or will it be a government funded issue with the scope of the problem? Granted if systems are running high temp the home owner would have been better off with a conventional cast iron boiler in my opinion.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Jean-David Beyer Jean-David Beyer @ 7:53 AM
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    As a homeowner who will probably get stuck with the tab,

    I expect the government will not pay for any of it. There is probably no extremely large political party that represents homeowners of boilers with PVC venting systems to get the government to do anything. I know here in New Jersey we do have a state program to help homeowners remove in-ground oil storage tanks. My tank was removed in May 2009. The state has my grant application for the cost of remediation not covered by insurance. But just recently I was informed that the program is out of funds, and people are having to wait three years or more before there will be funding for it. I may have to wait less because my application was received long ago.

    Judging by the Internet price of the amount of stainless needed to replace the exhaust of my system, it is about the same as the cost of the building permit I paid to have the boiler, hot water heater, and converting to two zones done. Around the cost of a 3-year service contract for my heating system. Of course, I would need to add labor, overhead, and profit to the cost of the stainless itself. I suppose I could do it myself, but I do not propose to do that.

    Having measured the outside temperature of the PVC (111F) when making hot water for the indirect, and noticing no color change  of the exhaust pipe, it does not look like an emergency for me. Most of my house is radiant, where the return temperature is always less than 120F, and sometimes about 75F. The other heating zone is always less than 135F, and sometimes slightly less than 110F. The domestic hot water is the hottest, where the return temperatures can go up to 160F or so, for 5 or 10 minutes a few times a day (2 or 3, as far as I can tell).

    I would like to find out if there is any need to replace the pipe before a color change. I would very much doubt I would be better off with a cast iron boiler, since the only high temperature use is for the indirect hot water heater that can get up to 175F supply temperature with about 155F return.
  • Jack Jack @ 9:04 AM
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    PVC for vent systems

    Regardless of its performance over the years I think that as an unlisted product for the application, its days are numbered. Charlotte went thru some linguistic gymnastics a while back in the "Suitability of PVC for vent systems" letter. Essentially they acknowledge that it is not listed, say there isn't enough of an installed base to make a reasoned assessment of it suitability for venting (nonsnese) and then say it is up to the equip manuf to determine the best material for their system. This type thing is just blood in the water for the Trial Lawyers Assoc. This one will make polybutylene and Plexvent look minor. I hope I am wrong!

    A part of this suitability discussion goes to the type of appliance. A warm air furnace that never gets its filter changed will run up on limit and cycle on and off on that limit. Once a boiler has heated and cooled its operating fluid becomes kind of an inert fluid and there is not much scaling...normally, that will take place. I have seen quite a bit of brown PVC on tank water heaters. I think this has been on mostly high duty cycle apps.

    When Rinnai was designing their condensing water heaters we told them that for competitive purposes we needed a PVC vent system. Rinnai Japan Engineering took one look and said, No joy on PVC and we now have a Polyprop concentric vent. With their explanation, I have to agree with them. Every gallon of water going through a tankless water heater is fresh water. If, over time, the unit scales up you end up with an increased stack temp. A limit in the stack could be a solution, but it shows the product to be unreliable (hot/cold cycling shower) and I'm of the opinion that a limit is a safety control, not an operating control. Where PVC can take 156F the polyprop will take 250F. I'd rather take the high road on this with tankless and am pleased with the decision RJ engineering made.

    I think a part of the problem PVC will have going forward is the availability of the Polyprop in the market. It is a better material and as the discussions heat up on PVC, and they are, the pressure will lead to the higher spec product...whether you need it or not.

    Today, where is pvc NOT legal for use?
  • Jean-David Beyer Jean-David Beyer @ 9:41 AM
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    Today, where is pvc NOT legal for use?

    It must be legal where I am. My PVC is in plain sight, and it was inspected and passed by the gas company man, and three different inspectors: electrical, plumbing, and fire protection. Of course, they also approved my ungrounded, unbonded CSST as well, also in plain sight.
  • N/A @ 4:22 PM

    whats CPVC

  • Tim McElwain Tim McElwain @ 5:53 PM
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    CPVC is

    chlorinated poly vinyl chloride which can operate at a higher temperature than straight PVC.

    Maximum operating temps:

    ABS Schedule 40                            160 ° F
    PVC Schedule 40                             140° F
    CPVC Copper Tube Size                   180° F
    CPVC Scheule 80                             200° F
    This post was edited by an admin on May 14, 2011 5:58 PM.
  • Tim McElwain Tim McElwain @ 10:26 AM
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    It remains to be seen

    as to what the outcome will be with all of this. There are pros and cons among the contractor side of this discussion as is certainly evidenced here.. A lot of that driven by cost of plastics versus stainless steel I am sure.

    I have witnessed several times in the past five years PVC and CPVC which show signs of stress from over temperature especially in cases of indirect connection to the boiler system. I have also seen it on vents on warm air furnaces perhaps the result of poor maintenance such as keeping the filter changed, cleaning the secondary heat exchanger at least once a year, insufficient return air. etc.

    I was involved way back with the Plexvent and Ultravent fiasco. My company a gas utility that had the responsibility for testing for approval to sell in our state tested both of them. Our preliminary findings found no problem at all with the two products. We did however keep the plastic as a vent system on some of our lab training equipment. I began to notice a change in the fittings especially after about 10 months operation on a continuous basis with classes in the lab firing the equipment every day. After 18 months I brought the change to the attention of my superiors and they viewed my findings but no action was taken. Within a two and a half year period we had to add more hangers to support what was a definite sagging affect taking place. The original support system was to manufacturer specs.It was at the end of three years my company took action to ban future use of it until more testing could be done by the manufacturers. It was several years later it was banned. That product was used by many contractors at the time and most said they had never had a problem. 
  • Ron George Ron George @ 10:51 AM
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    PVC is not currently approved as a venting material.

    PVC is not currently approved as a venting material for combustion gasses.  I see where some have used examples where they have seen PVC used somewhere else. That is a "Monkey see, monkey do" syndrome.
    The manufacturers are wrong when they reccomend PVC for use as a venting material because it is not listed for that purpose.  The code addresses that and overides the manufacturers instructions if they are less stringent than the code requirement for all products to be listed and labeled for their intended application.
    The ASTM D1785 standard clearly states PVC is not for use for venting combustion gasses.
    Many Inspectors are unaware of this also.
    I would not want to be a defendant in a trial and use the defense strategy of "I saw someone else do it wrong so I did it wrong"  Two wrongs don't make a right.  A thousand wrongs don't make it right.  We should make a habit of reading the codes and reading the product standard.  
  • TomS TomS @ 11:32 AM
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    1998 recall on plastic vent

    At least in the year 1998 it appears that PVC was not listed in this recall notice.
     U.S. Consumer Product Safety Commission
    Office of Information and Public Affairs
    Washington, DC 20207
    CONTACT: Russ Rader
    February 24, 1998
    (301) 504-0580 Ext. 1166
    Release # 98-072       CPSC, Manufacturers Announce Recall Program to Replace Vent Pipes on Home Heating Systems
    WASHINGTON, D.C. - In a landmark action, virtually the entire furnace and boiler industry together with the manufacturers of high-temperature plastic vent (HTPV) pipes have joined with the U.S. Consumer Product Safety Commission (CPSC) to announce a recall program. This program will replace, free of charge, an estimated 250,000 HTPV pipe systems attached to gas or propane furnaces or boilers in consumers' homes. The HTPV pipes could crack or separate at the joints and leak carbon monoxide (CO), presenting a deadly threat to consumers.
    CO is a colorless, odorless gas produced by incomplete burning of carbon-based fuel, including natural gas and propane. The initial symptoms of CO poisoning are similar to the flu, and may include dizziness, fatigue, headache, nausea and irregular breathing. High-level exposure to CO can cause death.

    To determine whether they have HTPV pipe systems that are subject to this program, consumers should first check the vent pipes attached to their natural gas or propane furnaces or boilers. Vent pipes subject to this recall program can be identified as follows: the vent pipes are plastic; the vent pipes are colored gray or black; and the vent pipes have the names "Plexvent ," "Plexvent II" or "Ultravent " stamped on the vent pipe or printed on stickers placed on pieces used to connect the vent pipes together. Consumers should now check the location of these vent pipes. For furnaces, only HTPV systems that have vent pipes that go through the sidewalls of structures (horizontal systems) are subject to this program. For boilers, all HTPV systems are subject to this program. Other plastic vent pipes, such as white PVC or CPVC, are not involved in this program.

    After checking the vent pipes, consumers should call the special toll-free number (800) 758-3688, available between 7 a.m. and 11 p.m. EST seven days a week, to verify that their HTPV pipe systems are subject to this recall program. Consumers with eligible systems will receive new, professionally installed venting systems free of charge. Additionally, consumers who already have replaced their HTPV pipe systems may be eligible for reimbursement for some or all of the replacement costs.

           The program came about as a result of mediation among 27 participants manufacturers of HTPV pipes and manufacturers of natural gas or propane-fired boilers and mid-efficiency furnaces. This is the first time that CPSC has used a mediator to bring together all segments of an industry to implement a program for the benefit of consumers.

    All consumers should have their fuel-burning appliances inspected each year to check for cracks or separations in the vents that could allow CO to leak into the home. In addition, CPSC recommends that every home should have at least one CO detector that meets the requirements of the most recent Underwriters Laboratories 2034 standard or International Approval Services 6-96 standard.

    The following lists the manufacturers participating in this program.


    Armstrong Air Conditioning Inc.
    Bard Manufacturing Co.
    Burnham Corp.
    Consolidated Industries
    Crown Boiler Co.
    The Ducane Co. Inc.
    Dunkirk Radiator Corp.
    Evcon Industries Inc.
    Hart & Cooley Inc.
    Heat Controller Inc.
    International Comfort Prod. Corp.(USA)
    Lennox Industries Inc.
    Nordyne Inc.
    Peerless Heater Co.
    Pennco Inc.
    Plexco Inc.
    Raypak Inc.
    Rheem Manufacturing Co.
    Slant/Fin Corp.
    Thermo Products Inc.
    The Trane Co.
    Trianco-Heatmaker Inc.
    Utica Boilers Inc.
    Vaillant Corp.
    Westcast Inc.
    York International Corp.

    The U.S. Consumer Product Safety Commission protects the public from the unreasonable risk of injury or death from 15,000 types of consumer products under the agency's jurisdiction. To report a dangerous product or a product-related injury and for information on CPSC's fax-on-demand service, call CPSC's hotline at (800) 638-2772 or CPSC's teletypewriter at (800) 638-8270. To order a press release through fax-on-demand, call (301) 504-0051 from the handset of your fax machine and enter the release number. Consumers can obtain this release and recall information via Internet gopher services at or report product hazards to [email protected]. This Website is Powered by Online-Access® All Rights Reserved © 2001-2011

    Read more:
    All content may be subject to copyright by Online-Access, Inc. To view the Terms & Conditions, visit
  • N/A @ 11:52 AM


    not acceptible?
  • Tim McElwain Tim McElwain @ 2:49 PM
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    No it is not

    an acceptable venting material as far as I know it never was. We have had galvanized (single wall)  24 to 26 gauge for Category I non condensing and also "B" vent which is double wall also for Cat I.

    Are you talking about the aluminum flexible vent for lining chimneys?

    Also dryers use an aluminum exhaust?
  • Jason Jason @ 5:47 PM
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    Other countries

    I have read that almost if not all other countries have banned PVC for venting heating appliances. What do we think we know that they do not?
    I was told by a European contractor one time that we Americans only think we know something about mod/cons and we don't know sh*t. They have been doing mod/cons for over twenty years and have learned much in that time but we are too good to listen.
    Take it for what it is worth. I wasn't listening.
  • Chris Chris @ 7:01 PM
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    Catch 22 Jason

    Triangle, Buderus, Baxi all allow PVC over here? The question then becomes, why? You are correct in that they don't use it across the pond. They all use either a Coaxial or Poly Prop.

    I do have a question for ME and HR. Why does Lochinvar require CPVC before the transition to PVC? I would ask Glen Stanton the same for the Burnham Alpine? Do these two mfgs know something?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Mark Eatherton Mark Eatherton @ 9:44 PM
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    You'd have to ask them....

    While you're at it, ask them why they are the only manufacturer who requires 1" of clearance around all venting and water piping...

    I don't know for a fact, but I suspect that their lawyers had something to do with it. I am sure they maintain a regular staff of legal beagles to handle the day to day threat of lawsuits, and after they read the I&O manual for the Knight, being used to the old cat 1 B vent venting, they decided that it would be a good direction to go with the 1" minimum clearance when everyone else sees fit to go zero clearance...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • VictoriaEnergy VictoriaEnergy @ 9:51 PM
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    I think the US needs a standard, similar to the ULC S628 certifying vent material as to suitability and temp limits.

    Appliance manufacturers should be required to have manual reset limit switches on their vent outlets consistent with the vent standard.  I don't think software based, or auto resetting limits are suitable.  Resetting the whole boiler or simply waiting clears the fault and leaves owners and poorly trained service staff thinking they have an electronics glitch. 

    There's no reason why appliance manufacturers couldn't make the vent switch part of the vent transition adapter, so if you installed a unit with stainless vent, the switch in the transition part has a higher setting.

    The only issues I've seen in the field with PVC have been joint separation issues, usually from primer not being used on initial assembly.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
    This post was edited by an admin on May 15, 2011 9:53 PM.
  • pipe4zen pipe4zen @ 6:25 AM
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    speaking of cement and primer

    was it ever intended for exhaust venting ?
    With all the expansion/contraction of the pipe and fittings.
    I always try to use the heavy bodied formula glue. Comes out like snot, and is expensive but rarely do I get a leak, (when I test PVC for plumbing). The regular bodied stuff is just too watery for me, and it seems like your holding the fitting together forever before it sets.

    I would prefer a mechanical joint instead. But that would probably mean the vent materials would cost just as much as the mod/con boiler.
  • SLO-115 SLO-115 @ 8:23 PM
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    Victoria energy remember

    The first gen condensing gas forced air furnaces. Olsen and keeprite both had manual reset limits on the outlet of the venter motors, they were set for 120'f. Now look at all the junk out there, no limits at all for overheating venting
    This post was edited by an admin on May 18, 2011 8:24 PM.
  • Mark Eatherton Mark Eatherton @ 11:40 AM
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    Am I the only one who see's a potential conflict of interest here...

    It looks to me like he (Mr. George) has a BIG dog in this fight.

    (8.F.Y.I. I have a patent pending for a temperature sensor in the flue outlet of a boiler or water heater to sense excess temperatures and shut off the burner to prevent damage to PVC flue pipes. The controls allow intermittent operation to prevent freze-ups and it sounds an alarm to alert the homeowner of a problem. With this technology, Boiler and water heater manufacturers can utilize plastic vent pipes without worries of overheating. It goes without saying that installing a water softener in hard water areas is vitally important.)

    Thank you for full disclosure Mr George, but you use an article as a lightning rod, and then stand by and offer to sell early lightning strike detection equipment?

    I agree that this is an issue that needs to be addressed, and it appears that the codes are making some effort in that direction. It just appears to me to be a conflict of interests unless the author completely dis-associates himself from the code writing authority.

    Please feel free to correct me if I am wrong...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Ron George Ron George @ 7:41 AM
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    Ron's Reply

    The article was written before there was a patent.  I realized the opportunity to file for a patent after the article was written.  The article was based on facts.  I simply realized the problem and report about it.  After reporting about it I filed for a patent for the technology to correct the problem.  Feel free to check the date on the application.  That is the American Way.  When I recognized a problem I reported on it and then thought about it.  while thinking about it, I came up with a solution for it.  My patent application did not change anything. 
    The codes do not allow PVC flue pipes and never have.  The manufacturers publish in their literature that you can use PVC instead of Stainless steel to make their condensing equipment more competitive with non-condensing equipment. 
    I have come up with a way to allow you to use PVC if the manufacturers’s want to add the safety controls to their equipment.  There should also be an industry standard developed to test the controls.  Currently we do not have that option.  We can always use stainless steel flues.  That has always been the only code approved method of venting gas fired appliances.  Even is an inspector allowes PVC Venting because he is not fully aware of the issue, that does not make it legal as far as the code is concerned.  You cannot point to an installation and say the inspector approved this one so they must all be acceptable.    
    The PVC standard referenced in many manufacturers product standard listing contains language stating the the PVC pipe in this standard is not intended for venting combustion gasses"  Other manufacturers have language that simply allows PVC venting materials without any references to a standard.    There is no way for a manufacturer to prevent flue gasses from rising if there is hard water supplied to a system or is a filter is not cleaned properly.
    If you read the codes and the standards, they clearly do not allow PVC for venting combustion gasses.
    Please don't throw stones at me because I found many failed systems, reported on this and then had an Idea to make it better.   
  • Mark Eatherton Mark Eatherton @ 8:08 AM
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    Fair enough then...

    I will give you the benefit of time and assume the patent idea was after the fact.

    So, what would YOU do if you were the king?

    It's too late to close the gate, the cattle are already out roaming around the country side, legal or not.

    There was not a lot of response in regards to my asking for how many completely failed systems people have come across in the field.

    If I were a plastic PVC pipe manufacturer, how far would I have to go to get my pipe certified for applications including the handling of flue products?

    Sorry about casting stones, but you must admit, there does appear to be some potential conflicts of interest on the outside. I'm not one to cast stones unless I see a need to.

    So, one of my previous questions that I'd really like you to address is "Why are installers not required to perform a combustion analysis on EVERY piece of fired equipment to help eliminate the production of Carbon Monoxide?"

    They should be required to leave a copy of the analysis attached to the equipment, and it should also be mandatory to have the appliances checked every 2 years with the obligatory report again left on site.

    Carbon monoxide is THE most preventable means of inadvertent poisoning in the world today. Why have the codes not addressed this?

    Dave Yates and myself went through the process of trying to get combination DHW/space heating systems outlawed, and it appeared to me that the codes were quite strongly influenced by money (water heater industry) and backed up by the HBA (What's it going to cost, and what are the perceived benefits to the home builder?) with little to no regards to the end user. Personally, I was not impressed with the reaction of the code officials in regards to our attempts to eliminate inadvertent exposure to large quantities of Legionaires Disease. They seemed quite lackadaisical in their efforts, and also seemed highly influenced by the water heater manufacturers wishes want's and needs and disregarded the health concerns we raised, which have been documented by a major recognized authority (CDC).

    After having been through this process, I probably would not waste my time and effort to go through it again... regardless of how many lives we could save.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • TonyS TonyS @ 8:16 AM
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    Mark. stop garbaging this thread up

    with the FACTS!!. They are on a Snipe hunt and by God they are going to find one!!!
  • Ron George Ron George @ 10:25 AM
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    Ron's Reply

    To answer your question, "Why are installers not required to perform a combustion analysis on EVERY piece of fired equipment to help eliminate the production of Carbon Monoxide?"
    The issue of carbon monoxide is important, but not in this case. ALL combustion creates Carbon Monoxide.  The issue here is the flue gas temperatures exceed the temperature limits of the flue materials (PVC).  In most cases the excess is not too bad and discoloration occurs.  As time passes in hard water areas, the heat exchangers scale up on the water side of the combustion flues and then the combustion gasses cannot transfer heat into the water.  When this happens, the flue gas temperatures rise. If the temperatures rise high enough the pipes sag and melt.  At that point, carbon monoxide becomes an issue.   

    I agree the appliances should be checked at regular intervals with documentation left on site.  We do this with backflow preventers. I also feel there should be deliming connections on all hydronic heating equipment in case they are needed.

    The code does address flue venting options.  you can use non condensing equipment or if you use condensing equipment the correct category vent must be installed.  PVC is not listed to any category.   A few manufacturers appear to be the ones giving out misinformation about he use of PVC as a flue vent for combustion gasses.   

    I agree with you and Dave on the elimination of combination units for DHW/space heating systems.  I have seen many scald injuries associated with combined systems that were too hot because they were undersized and the temperatures were cranked up to compensate.  The two systems typically operate at different temperature ranges.  Either the building will have poor heating or there is a risk of scalding.  The proper system design requires knowlegeable maintenace personnel.  I find these days not many companies keep good maintenance personnel on staff for such sophisticated systems.  I also agree with your observations of the lobbying efforts and strength of the WH manufacturers and the HBA. 

    I also agree many code officials are not up to date on the Legionella issue.  F.Y.I.  I developed a website and formed an organization aimed at educating the industry about how to prevent Legionella bacteria growth in building water systems. 
    I have served on a few hot water design and product standard committees that had manufacturer participants that spoke up and said they did not want to use the "L" word because then they would be acknowlwdging there is a problem. 
    The CDC seems to have taken a reactionary verses preventative approach in their Legionella efforts.  
  • Charles Johnson Charles Johnson @ 10:58 AM
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    Re: CO prevention

    Good point Mark about CO poisoning.
    The sad fact is most of it goes undetected as low level poisoning that make people sick but don't make the news.  It is almost always misdiagnosed by the Doctor. 
    If there was a standard you talk of that required all combustion appliances to be tested, it would prevent more poisonings than current codes ever can.
  • Mark Eatherton Mark Eatherton @ 11:17 AM
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    At a minimum...

    the codes SHOULD require the installation of a CO alarm, which they currently don't in most states.

    Then there is the problem of time weighted CO values... Obviously no concensus there.

    And then there is the issue of battery maintenance on the detector. I've seen statistics somewhere regarding the fact that dead batteries were found in smoke detectors, and had they been replaced, lives would have been saved. It's a sobering statistic.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • HDE HDE @ 10:05 AM
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    Not a new idea

    What about all the gas fired condensing appliances that already have a flue temp limit device? I keep hearing 140 degrees, but sch 40 DWV PVC has a max temp rating of 158.

    For instance my Navien Tankless has a 149 degree flue overtemp sensor. I know there are other appliances that have them also. CSA approves this safety to allow PVC venting.
  • Ron George Ron George @ 11:19 AM
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    PVC Temperature limits.

    The maximum temperature limits for PVC Piping is 140 degrees according to the technical manual for the PVC piping manufacturers.
    Check your facts.
    The temperature limit of 158 is not for PVC pipe. 
    How does PVC pipe behave at different temperatures?
    PVC pipe exhibits decreasing pressure rating and stiffness with increasing temperature.  As with dimensions, the pressure ratings and published pipe stiffness figures for PVC pipe are listed at an operating temperature of 73F.  To determine the pressure ratings and stiffness of PVC pipe at higher temperatures, multiply the pressure rating or pressure class and the stiffness / deflection by the pipes de-rating factors at that temperature.  An example of a table of PVC pipe de-rating factors is shown below. Consult with the manufacturer of your pipe for specific data. The typical upper limit for continuous use of PVC pipe is 140 F.

    The following are the primary applications for PVC pipe folloed by the standards.
    1. Water Pipe:
    1. ASTM D1785, Sch 40 and 80 pipe (1/8" to 24" sizes)
    2. ASTM D2241, SDR pipe (SDR 13/5 to 64 - 1/8" to 36" sizes)
    3. AWWA C900, Water mains 4" through 36"
    4. AWWA C905, Water transmission pipe 14" through 36"
    5. AWWA C909, Molecularly Oriented Polyvinyl Chloride (PVCO) Pressure Pipe, 4" to 24" for Water Distribution 

    2. Drain, Waste & Vent Pipe:
    1. ASTM D2665, Sch 40 (Can be dual marked D1785)
    2. ASTM F891, Cellular core Sch 40, 1 1/4" through 12"

    3. Process Pipe:
    1. ASTM D1785 & D2241, Iron Pipe Size OD pressure pipe

    4. Sewer Pipe:
    1. ASTM D3034, SDR pipe, 4" through 15"
    2. ASTM F891, Cellular core sewer pipe ODs, 2" through 18"

    5. Drain Pipe:
    1. ASTM D2729 (2" through 6") or D3034

    6. Folded PVC pipe:
    1. ASTM F1504 - special product for relining of underground pipes, 4" through 15"

    None of these pipes are listed for combustion flue gas venting. 
  • HDE HDE @ 5:08 PM
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    Mr. George,

    PVC venting had a pressure during operation of what? Not even close to 1 PSI, so I don't understand your plumbing rating argument there.

    Arguing temperature derating meaning stress and pressure operating failure will occur when there is no significant measurable pressure?

    At 140 degrees 3" still has a burst pressure rating of over 100 psi, but who cares were not talking about fluids in the pipes.

    Is this the case of a plumbing engineer straying into HVAC waters?
  • icesailor icesailor @ 7:14 PM
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    What PVC pipe and fitting manufacturer approves and recommends their PVC pipe and fittings for appliance exhaust?
    Just because the equipment manufacturer "allows" it doesn't mean the manufacturer approves it being used in that application.
  • HDE HDE @ 1:37 PM
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    The answer would be IPEX, it's the same material with approval stickers now costing more. A requirement in Canada
  • Ron George Ron George @ 12:16 PM
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    PRessure vs Temperature ratings for Plastic piping

    PVC pipe is rated at 100 PSI at 73 degrees F
    At 100 degrees F PVC is rated at 60 PSI
    At 120 degrees F PVC is rated at 40 PSI
    At 140 degrees F PVC is rated at 20 PSI
    At temperatures near and above 140 F the PVC pipe starts to become soft and pliable.  If there are any stresses of forces acting on the pipe it could melt and collapse blocking off the flue and causing a carbon monoxide leak in the building.
    See the link below for temperature pressure ratings for PVC pipe:
    The standard for PVC pipe specifically states it is not for venting combustion flue gasses. 
  • SLO-115 SLO-115 @ 7:35 PM
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    ULC-636 tested and approved
  • Ron George Ron George @ 12:23 PM
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    ULC is a Candian Standard

    ULC is a Canadian UL Standard and is not referenced in the codes in the United States.  Therefore, it does not apply in the United States.
  • Chris Chris @ 8:08 PM
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    What It Boils Down To

    Is very simple. Show the testing data. Mfgs that allow PVC venting should via the Freedom of Information Act via the DOE pr the Consumer Protection Agency have to show the public the testing data that PVC is a safe product for the removal of flue gases. We have statements from the mfgs of the product itself that clearly states it has not been tested. So show us the data.

    Whether you have used it for 100 yrs with no problems has no bearing. Trial and error to justify its use is not in the best interest of public saftey. For me that is the issue I have a problem with. If you have the data proving it is a safe means of removal of flue gases then lay it on the table for all to view.
    If it's safe then so be it. The reluctance of mfgs to show or anwser questions concerning this subject itself raises questions. Plex Vent was caught with somewhere  in the 250K installation range divided up between numerous mfgs. Thus the liability cost to them was a micro dot compared to what the cost would be if they were held liable with PVC vent issues.

    With M&G and Centrotherm daily getting the PPs products approved for equipment I can see this issue slowly and quitely going away over the next couple of yrs. PPs will keep the vent cost in a reasonable price range.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on June 1, 2011 8:26 PM.
  • pipe4zen pipe4zen @ 5:38 AM
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    What it really boils down to

    Is very simple, the 140F degree ASTM specification that keeps getting referred tp here clearly states 'this specification is for pressure systems using PVC pipe and fittings'. ' This system is intended for pressure applications where operating temperatures will not exceed 140F.'

    So once again, an ASTM needs to be added for PVC in a non pressure/temperature rating.

    I suspect testing agencies are on it but would take years to test and approve. Then this issue will go away, and PVC pipe manufacturers will line up along side furnace and boiler manufactures for there use.

    Until then, the code I read clearly approves of this as long as equipment manufacturer instructions are followed.

    There is no code forbidding its use.
  • Ron George Ron George @ 10:24 AM
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    The codes requires all products to be listed for their intended application

    The code requires all products to be listed for their intended application.
    The standard for PVC pipe does not include venting combustion flue gasses.  In fact the ASTM standard specifically mentiones the PVC pipes are not intended for venting combustion flue gasses.
    Therefore The code does not allow PVC for venting flue gasses even if the manufacturer says you can.  There is a section in the code that addresses conflicts that mentions.  When the manufacturers' instructions conflict with the code language, the more stringent language applies. The more stringent language is the listing requirement. 
    Therefore the way I read it, the code DOES NOT allow PVC for venting flue gasses.
  • pipe4zen pipe4zen @ 2:29 PM
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    Where is the code?

    Please show me the code that specifically say a furnace or boiler or water heater can not be venting any combustion exhausts using PVC schedule 40 pipe.

    Any code in the U.S. (ICC, Uniform, Any state code) . Please post it for all, thanks.

    ASTM is not a code, its a testing standard . The way you read it is incorrect, otherwise building inspectors across the nation would have also come to the same interpetation. And local codes always supercede any minimum national codes or standards.

    This polypropylene pipe that is mentioned here as a replacement to PVC is still only rated up to 180F. IMO, not much better than PVC.
  • Plumdog Plumdog @ 7:39 AM
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    You guys worry too much!

    I know for a fact that PVC can be used for ANYTHING! I just ran across an expansion tank (on a 1,257,000 btu snowmelt boiler) that was made out of a piece of 6"cell core PVC pipe. It even had a clever little "sight glass" made of pex so you could tell how much air was in the top. Also the support stands were made of 3" PVC with nice little cradles sawn in to spread out the load. PVC can be used for lawn funiture, chicken coops, pontoon boats, and most anything where costly materials are not an option. 
  • Ron George Ron George @ 11:34 AM
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    PVC has many uses - compressed gasses is not one of them.

    PVC pipe is not intended to be used with any compressed air or gasses.  This is what an expansion tank is doing.  PVC pipe will explode with vilent force if it is subjected to compressed gasses and it is exposed to physical damage.  Most PVC pipe technical manuals are full of these warnings.
    As for other uses of PVC pipe.  I used 4 inch PVC Pipe to make a Goal post in my backyard so my son could practice kicking field goals.  But I would never use it for venting combustion gasses or for compressed gasses.  I tried to attach a video of a test that shows a piece of 6 inch PVC pipe with 100 PSI exploding when put under stress.  It looks like a bomb going off.  The video is apparently too big for the blog. 
    Reminder: Do not use PVC pipe for compressed air or gasses and do not pressure test PVC pipe with compressed air.  The storred energy of the compressed gasses propels pipe shards like shrapnel from a hand grenade when it explodes.
  • HDE HDE @ 1:42 PM
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    Definitely in agreement on that subject
  • Tim McElwain Tim McElwain @ 3:28 PM
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    Ron what is your

    take on:
    Anyone using InnoFlue?This is a product from Centrotherm Eco Systems. It is a polypropylene vent system. It is based on ULC S636. It can be used up to 230°F or (110° C). it is zero clearance to combustibles. It can be used with oil, propane and gas fired appliances.

    They claim cost comparison on 3" diameter 24 foot long system with 4 elbows. Estimated labor rate of $40 per hour PVC material cost $167, labor $120 total $287. For CPVC material $520 labor $120 total $640. Compared to InnoFlue material $172 labor $60 total $232. Very interesting.

    To check it out go to  
  • pipe4zen pipe4zen @ 5:23 AM
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    As far as I can tell

    there also is no difference in IPEX system 636 listed PVC pipe or CPVC pipe. It's just PVC that was tested to 230F degrees , under no pressure, it also has orange stickers listing its use for combustion flue gas.
  • Ron George Ron George @ 9:48 AM
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    It looks like a good alternative to PVC

    Polypropylene plastic pipe material can take higher temperatures than Polyvinyl Chloride pipe materials.   I think Polypropylene is the way to go for condensing equipment if a consensus standard can be developed in the U.S.  It appears from a few posts that some people don't understand there is a clear difference in pipe materials and the materials ability to handle different temperatures.  PVC can only handle temperatures up to 140 degrees F and should not be used for venting combustion gasses because most heating hot water and domestic hot water systems operate at or above 140 F and the flue gas temperature is always above the system operating temperature. If a furnace is not maintained and the filter is dirty, you can have reduced airflow which leads to increased flue gas temps.  According to the manufacturers: the various pipe materials can handle the following temperatures:

    PVC (Polyvinyl Chloride) Schedule 40 = (White)                       140 F

    ABS (Acrylonitrile butadiene styrene) (Black) Schedule 40 =    160 F

    PVC (Chlorinated Polyvinyl Chloride) (tan) Copper Tube Size = 180 F

    CPVC (Chlorinated Polyvinyl Chloride) (Gray) Schedule 80 =      200 F

    PP (Polypropylene) Schedule 40 =                                                   230 F

    As you can see there is a type of Polypropylene that is clearly the best choice of the plastic materials listed above.  Although there are some virgin polypropylene pipe materials that are intended for use in lab waste and pure water systems that are very soft and they would be less resistant to heat than the materials listed to ULC S636.  Additives are added to the polypropylene to increase its resistance to heat.  The wall thickness and the additive will affect the materials ability to withstand heat.  Not all Polypropylene can take 230 F Additives were included with various types of polypropylene lab waste fittings to reduce the flame spread and smoke development ratings in order to get approval for plenum spaces. I believe the adative in that case was silica sand. The same or different additives may or may not be used in the ULC S636 listed pipes to increase the heat resistance of the piping.
    We quickly need to get an industry standard started through the ASTM or ASME standard writing organization for plastic flue pipe materials.  The standard working group needs to have a consensus of installers, manufacturers, engineers and other experts.  When the standard is complete, then the testing labs can test the materials to the industry standards and then list and label or mark the products as meeting the standard.  The listing and labeling portion is important for inspectors to be able to know which products meet the standard for flue gas venting, After the standard is developed, then the Model codes in the US can accept the plastic flue gas materials.  I suspect the PVC and ABS would not pass the test otherwise this would probably have already happened.  Until then, there is nothing allowing PVCs use in the codes.  PVC is clearly not allowed by code because it is not a listed and labeled system, unless it is utilized under an engineered system in which the engineer has to provide a testing report and inspect the installation.  Until there is a standard referenced in the code and the products are listed to that standard, they are not allowed.  Even Polypropylene systems at 230F can experience problems if the flue gas temperatures exceed 350 degrees F which is very possible in cases where there is poor water quality and/or poor maintenance. 
    I think it is important to require either annual inspections of boilers and water heaters utilizing plastic flue pipes for problems or require water softeners and temperature sensors on the flue gas outlet. 
    Until then, listed and labeled Stainless Steel flues are available and approved by the code for condensing equipment.

  • icesailor icesailor @ 8:02 PM
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    Violent PVC:

    Ron is correct on the volatility of PVC under pressure. Especially when cold. Where I work, the water department started using PVC water mains on new expansions. They went to make a service tap on a 10" PVC main in February a few years ago and when they started to drill, the pipe fractured and exploded. It almost drowned the person in the trench. These problems continued. There are now very precise procedures to be followed when tapping PVC water mains. The company now uses only ductile iron for water mains.
    I have seen a few strange failures of PVC that no explanation could ever be found.
    But I ask again, does Charlotte Pipe list their PVC for anything but water, drainage or sewerage? 
  • Ron George Ron George @ 11:02 AM
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    Reply to Icesailor

    Ice man,
    I have talked to Charlotte pipe reps and they indicated Plastic pipe can be used for many things so that is why they have a free "Plastic Pipe Technical and Installation Manual" available for downloading from their website.  The manual has engineering data and performance limitations for ABS, PVC and PVC pipe.  PVC DWV pipe is non-pressure applications.  See page 40 for temperature ratings for PVC pipe.  See pages 109 - 115 for other warnings.  Pay particular attention to Page 115. which has the following text:
    Using Plastics for Combustion Gas Venting

    Charlotte Pipe recommends that inquiries about the suitability of plastic piping systems for venting combustion gasses should be directed to the manufacturer of the water or space heating equipment being installed. As stated in the International Code Council’s International Fuel Gas Code 503.4.1.1:
    Plastic Pipe and fittings used to vent appliances shall be installed in accordance with the appliance manufacturer’s installation instructions.
    Furthermore, several of the ASTM standards applicable to plastic pipe and fittings that Charlotte Pipe manufactures include the following note:This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.
    This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.
    They are basically saying if a manufacturer of a fuel burning appliance recommends the use of plastic pipe, there is no standard that they list to for venting combustion gasses and the manufacturer or the appliance is responsible for making sure there is a standard that will cover the perfomance of the product under the most extreme conditions the product will potentially see with their equipment.  Again, a product test in a standard should address the most extreme conditions for heat and other stresses not the most ideal conditions.  The conditions or maximum/minimum temperature and stresses for each material should be listed in a standard which should be titled something like "Plastic piping for venting combustion gasses". 
    The link the the Charlotte Pipe Technicaal and Installation data manual is below:
  • Plumdog Plumdog @ 8:35 PM
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    Kinda a joke, Ron

    I'm aware of the test procedures for plastic pipe, and danger of using compressed air for that purpose. I also insisted that the makeshift expansion tank be removed and replaced with an approved tank before I ever put pressure in that system. I also have vented many, many furnaces and boilers with PVC. As with anything in this Field of Endeavor, the craftsman can make or break the whole deal. I have seen my share of stainless systems that fell apart due to faulty workmanship.
  • pipe4zen pipe4zen @ 6:44 AM
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    I posted above about IPEX ULC 636 PVC approved pipe for flue gas venting being reted for 230F.
    I stand corrected, the pipe is only rated to 65C or 148F.
    But it is approved, same PVC just with orange stickers. So the way I see it, Charlotte pipe manufacturer has yet to get their pipe ULC 636 labeled. And others are taking advantage by saying their PP pipe is better, basically this entire thread is just one big advertisment .
  • icesailor icesailor @ 7:49 AM
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    PVC Venting:

    In other words (as I have been informed), if there is a problem with the PVC pipe and fittings when used to vent gas appliances, and there is a lawsuit, PVC is off the hook, they have no responsibility, and it is you and the appliance manufacturer and their "approval" for the product.
    Kind of like condoms. They are supposed to work but if they don't, you are on your own.
    I was told that in litigation gases, where there is litigation over PVC vent failures, the defense table has no Representative from the PVC pipe and fittings table. That tells me something. There is no responsibility from the manufacturers of the product. The manufacturers of the appliance are assuming the responsibility and you are responsible for the install.
  • Ron George Ron George @ 10:24 AM
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    Reply to Icesailor

    Ice man, Many PVC pipe manufacturers do not reccomend usng PVC for venting combustion gasses.  They list the limitations of their products in the technical manuals.  If someone chooses to use their product for something other than its intended purpose, they cannot be held responsible for a boiler or furnace manufacturer claiming you can use PVC pipe to vent combustion gasses.  Manufacturer's also do not have control over many of the other "redneck engineering" uses uses of PVC pipe. (furniture, structural supports, handrails, flag poles, fence posts, potatoe cannons, compressed air pipes, rocket launchers, air cannons, combustion gas flues, etc.)  There are no industry standards in the U.S. approving of most of these uses.
  • Ron George Ron George @ 12:39 PM
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    Website with lots of ides for use of PVC pipe 
    Not all of the ideas in the aboe website are safe. Some are comical and some are practical, but most are not approved uses for the product. This just shows the wacky ways PVC pipe gets used.  Duct tape probably falls into this same category. I call it "Redneck Engineering".  Many manufacturers have jumped on this bandwagon and in my opinion, they are taking a big risk if there is ever a problem and they are recomending PVC pipe for venting combustion gasses in their literature.
  • Tim McElwain Tim McElwain @ 10:30 AM
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    pipe4zen it was not my intention

    to open this forum for advertisement of anything. The issue here is safety both short term and long term. Mr George and I have no personal relationship of any kind. I invited him here to defend his findings on the PVC pipe issue. Healthy discussion and allowing all opinions to come forth is what solves problems if in fact there is a problem.

    I take some issue with the problem versus the patents pending and personally feel it is somewhat a conflict of interest. Mr George I am sure can defend himself on that issue. I have received several private e-mails voicing concern over his perhaps going forward and making money from something he is dealing with as a code person.

    Then there is a fact over and above the safety issue which is directly related and that is liability. After many years in this industry (over 55 years) I have found in court cases (I am a registered expert witness) that often the courts rule against the contractor who may have knowingly done something or used something which was questionable or in fact had no approval from a governing body. I am always first and foremost looking to help and protect my fellow technicians. I worked as a serviceman and educator in the industry for many years and am now strictly an educator. I am trying to help everyone to come to some conclusion on this subject. I interjected the discussion on polypropylene to perhaps find an approved solution.

    As for the several e-mails I have received accusing me of getting paid by some manufacturer or agency that is not true. My income is derived from my consulting and educating practice and I am not directly affiliated with any company. I do offer my consulting services to some control companies and have done consulting for a number of them. That does not however put me in any ones hip pocket.
  • Ron George Ron George @ 4:43 PM
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    Is 148 degree pipe listed to a standard not recognised by the code acceptable?

    Remember, most PVC pipe manufacturers in their literature do not reccomend PVC piping be utilized at temperatures above 140 F.  If you use the IPEX product, they allow 148 F for their product and with a temperature limitation of 148 F.  I must remind you, most boilers, water heaters and furnaces will have flue gas temperatures well in excess of 148 F.  Using the PVC in a system that exceeds those temperatures would be a violation of the pipe manufacturers product limitations. (even if it is the 148 F pipe)   Then the contractor takes on all the liability.  Most PVC pipe manufacturers have reviewed this and decided to stay away from endorsing PVC for venting combustible flue gasses because there is too much liability.  A few have offered it and I feel that is a gamble. It is just not safe. You can chosse to install PVC that is listed to ULC S636 and take a gamble that a mechanical inspector in the U.S. will accept that standard.  If you are ein Canada and you are sure the system is designed to operate with flue gas temps below 148 you are OK.  But, the standard is not listed in the codes in the U.S. and therefore not an approved standard in the U.S.  Canada has been allowing it, but there has been some controversy there too.  Good luck if you choose to gamble and install PVC.  Stainlees steel systems are available and if you join them properly (in accordance with the manufacturers installation instructions and seal the joints) it does not leak.   
  • Steamhead Steamhead @ 9:28 AM
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    What I'm getting from all this

    is that in a lot of cases, PVC venting has worked fine for years, as long as nothing has gone wrong with the unit being vented.

    But, if something does go wrong that boosts the flue gas temperature, it may not hold up. Then the lawyers come in, the manufacturer of the PVC argues that the PVC was not installed for its intended purpose, and we're left holding the bag.

    ME, I recall that when you intentionally deferred maintenance on your own mod-con to see what would happen, it dropped to something like 68% efficiency over a period of time. Do you recall if that resulted in elevated flue-gas temperatures?
    "Reducing our country's energy consumption, one system at a time"

    Steam, Vapor & Hot-Water Heating Specialists

    Oil & Gas Burner Service

    Baltimore, MD (USA) and consulting anywhere.
  • Mark Eatherton Mark Eatherton @ 9:40 AM
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    My little Munchkin has the SIT control with the flame suppression circuit on it. It will idle the burner back, regardless of the load, based on an increase in flue gas temperature. The low burner/heat exchanger thermal efficiency was evident with cold start up on high burn. I have enough flow meters and sensors on this boiler that I can tell you its thermal efficiency by the minute.

    Without the flame suppression circuit, I may have very well exposed the PVC to higher temperatures, but that is the reason the manufacturer uses the flame suppression feature.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Steamhead Steamhead @ 10:29 AM
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    Well, I'm sure

    that feature was one reason you chose the Munchkin ;-)

    On the units described in this thread where the PVC overheated- did any of them have this type of dial-back setup, or something else that would prevent overheating? I'd be willing to bet they didn't.

    It seems to me that the venting of traditional non-condensing equipment was designed with a certain safety margin (or evolved to that point) so it would hold up under extreme trouble conditions (for example, one of my Dead Men's Books describes improper coal-to-oil conversions where the stack was red hot). PVC venting of condensing equipment apparently does not allow this margin of safety.

    Unless and until there is a clear standard, maybe we should steer clear of PVC for venting.

    I'm heading out to a job- back later.
    "Reducing our country's energy consumption, one system at a time"

    Steam, Vapor & Hot-Water Heating Specialists

    Oil & Gas Burner Service

    Baltimore, MD (USA) and consulting anywhere.
  • Plumdog Plumdog @ 11:35 AM
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    flue gas temp sensors

    Trinity, Lochinvar Knight, Munchkin, and Prestige all are equipped with flue gas temp sensors. Pretty sure the Polaris water heater and the Lennox Complete Heat are so equipped as well. How many of the others are so equipped? I can't recall seeing them on scorched air equipment; but that doesn't mean they aren't there. I've seen supply air temps over 150 degrees, meaning the vent temps oughta be that high as well. Does anybody know how many 90% furnaces are out there? Better to have an airtight vent than a leaky metal vent. Hardly anyone seals the gores on the vent ells like your supposed to, and they leak CO all day long.
  • Jean-David Beyer Jean-David Beyer @ 2:30 PM
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    Flue Gas Sensor.

    My W-M Ultra 3 has a flue gas sensor, but the U-control (the controller for the boiler) will not fault until the flue gas gets up to 210F, so it will hardly protect 140F PVC.

    The default setting for their Indirect Fired hot water heater is 190F. I run mine at 175F. The domestic hot water is set to about 120F. The supply from the boiler can often get to 175F just before the domestic is satisfied. The return water is usually around 20F less, so say 155F. I suppose the heat exchanger is not 100% efficient, so the flue gas almost certainly exceeds 155F as it leaves the bottom of the heat exchanger. It travels through about 2 feet of uninsulated stainless pipe to the top of the boiler, where it transitions to 3 inch PVC. It might be slightly less than 155F at the top, but I would not want to make a bet on that. The outside temperature of the vent pipe I measured a while back, but I do not remember what it got to. Lots less than 140F, but it is probably the inside temparature that matters.
  • Chris Chris @ 2:52 PM
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    Beating A Dead Horse

    I think the horse has been mutilated to this point. Everyone is going to have their own opinion on this matter and rightfully so. In the end I just look at one thing.

    Trial and error is not in the best interest of public saftey. Just because it works itsn't the right way to do or justify a means. Why the heck do a heat loss. The system will work right. We all preach to those that come here to do the right thing and I would hope we would all want to see the testing data equipment mfg's have that allows PVC venting. If the testing data shows it is a safe means then so be it. Call the mfg of the equipment you use and ask for it. If its safe then what is there to hide.

    The lack of mfg's to respond on this issue within itself fuels the issue. Can we all agree on that. Why not use our voice as a whole to ask the questions and begin a new thread with what we find out. I'll start the thread with Viessmann's stance since they to my knowledge are the only mfg that has a printed statement concerning this issue. Everyone else can add from there what they have found out from the mfg of the equipment they use. It can be a no comment anwser if need be.

    In the end we are all professionals that do their best to do the right thing by code and the pride we carry in what we do. Until I see a stamp on PVC that says I'm using a safe vent material to remove combustion gases that's the day I will start using and recommending it. Until then, I'll stay away from it.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • HDE HDE @ 3:04 PM
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    "Until then, I'll stay away from it."

    Thats an interesting statement since many products you carry as a distributor vent with PVC.
    How will the owners and bosses that employ you feel about that?
  • Chris Chris @ 4:14 PM
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    I get up each morning as they do, put my pants on the same way they do, get my coffee like they do and give my best each day like they do. Do you honestly think I would give in my belief concerning this issue because someone told me to? That would never happen. There would also be a conflict of interest for me since when I do my Viessmann Trainings and we get to the vent topic I'm already swimming in that water. How can I preach one thing and then another? That's being an oxymoron.. By the way I only have two bosses, my 3-1/2 yr old son who is my world and my wife who is in Myrtle Beach visting her father..
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on June 5, 2011 4:19 PM.
  • HDE HDE @ 5:49 PM
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    I doubt Jim, Pete, Bill, Melissa, Justin & Rick feel that way. They desire sales, discriminate product due to your product venting principles and PVC could be your own personal demise, am I right?
    Sorry about the wife being your boss, when did you lose that one?
  • Chris Chris @ 6:47 PM
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    Don't Discriminate Product

    I never said I discriminated equipment just the practice of venting PVC when there are other means. Like I said, in my Viessmann classes the hot topic is always the venting issue. If I flip flop like a politician would I not loose my credibility?  Throwing names has no effect to my stance. Next time you come to Hawthorne stop by and say hi.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
    This post was edited by an admin on June 5, 2011 6:49 PM.
  • HDE HDE @ 9:11 AM
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    I will

    i haven't seen Rick or Jim in sometime. There was awhile there it seems I ran into them every 3 months or so.
  • Tim McElwain Tim McElwain @ 7:18 PM
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    This from Charolotte Pipe and Foundry Company

    Should Plastic Pipe & Fittings Be Used to Vent Combustion Gasses?

    Use of plastic pipe to vent combustion gasses produced by water and space heating equipment has become common practice among plumbers and builders. Some equipment manufacturers expressly recommend this practice. Occasionally, Charlotte Pipe is asked for its position on the use of plastic pipe and fitting products for this application.
    Industry Standards
    A variety of organizations produce standards for the construction industry. The best known of these organizations is the American Society for Testing and Materials International (ASTM). ASTM standards are developed by committees of industry experts and approved by the ASTM organization through a rigorous consensus process. These standards specify dimensional, performance and test requirements for various materials, including piping products. Manufacturers like Charlotte Pipe produce products that conform to these published standards. None of these standards addresses the use of plastic piping to vent combustion gases.
    Equipment Manufacturers
    Manufacturers produce a wide variety of gas-fired water and space heating equipment. These manufacturers may specify plastic piping for venting of combustion gases, citing these ASTM and other standards within their technical literature:

    ASTM D 2241    Specification for PVC Pressure Rated Pipe
    ASTM D 1785  Specification for PVC Plastic Pipe, Schedules 40, 80 and 120.
    ASTM F 891  Specification for Coextruded PVC Plastic Pipe With a Cellular Core.
    ASTM F 441  Specification for CPVC Plastic Pipe, Schedules 40 and 80.
    ASTM D 2661  Specification for ABS Schedule 40 Plastic Drain, Waste and Vent Pipe and Fittings.
    ASTM D 2665  Specification for PVC Plastic Drain, Waste and Vent Pipe and Fittings.
    ASTM F 438  Specification for Socket Type CPVC Plastic Fittings, Schedule 40.
    ASTM D 3311  Specification for Drain, Waste and Vent Fitting Patterns.
    ASTM F 628  Specification for ABS Schedule 40 Plastic Drain, Waste and Vent Pipe with a Cellular Core.


    Although these standards specify dimensional, performance and test requirements for plumbing and fluid handling applications, and are often used to refer to or describe a particular type of pipe, they do not address venting of combustion gasses. References to these standards by water heater or space
    heating equipment manufacturers should not be viewed as acceptance or approval by the ASTM for these applications.
    At present there is little data available on the safety or durability of plastic pipe products used to vent combustion gases. The ASTM has not addressed this application, and the available data is insufficient for the plastic pipe and fitting industry to develop consensus specifications or guidelines. Equipment manufacturers are most knowledgeable about their own products and are best­ equipped to determine how their gas-fired heating equipment should be vented. Accordingly, Charlotte Pipe recommends that inquiries about the suitability of plastic piping systems to vent combustion gasses be directed to the manufacturer of the water or space heating equipment being installed.
  • Tim McElwain Tim McElwain @ 12:12 PM
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    Here is some more

    input from a boiler manufacturers rep.

    Hi Tim,
    I felt a need to contact you regarding something that was lacking from all of the replies on PVC pipe..

    We call for the installer to use the CPVC venting material (30") that we provide to allow for cooling of the flue gasses to the tolerance that the PVC resin manufacturers call for or 140F. We also state that the PVC pipe being used be "SOLID CORE" Schedule 40 and NOT PVC "Cellular or Foam Core" pipe. Several years ago I was in my driveway outfitting one of our rolling display vans with two Alpine boilers that were stacked to demonstrate that capability. I decided to use PVC on one of them and Polypropylene on the other to show the different vent materials. When it came time to pick up some Schedule 40 PVC pipe from a local distributor, I was disturbed to find that very few RI distributors even carry "solid core" pipe anymore. All I contacted only had "Foam Core" in stock. To be politically correct in continuing my search for "Solid Core" pipe I ended up at The Home Depot.

    As Mr. George stated, many contractors prefer to use inexpensive items in an effort to stay competitive for fear of losing a job. The thing that troubles me is that I have been on numerous jobs where "Cellular Core" was used, either due to ignorance to the difference or due to trying to stay competitive. I had many installers remove the pipe and replace it with the correct pipe. We also call for CPVC pipe to be used when the piping is enclosed in a vertical or horizontal chase way as the pipe temperatures can elevate or stack in temperature without the surrounding air to effectively cool it. Mr. George is correct regarding the stance of the Pipe Manufacturers as clarified by the attached memo from Charlotte when we were giving consideration of PVC as a venting material for the Alpine and Freedom boilers.

    As for the jobsites that Mr.George was referencing in his article, he fails to give mention as to what grade of PVC pipe was used in the installations. I would probably think that at least some of them may have been "Foam Core" or even some other grade of PVC such as SDR pipe. I have seen PVC discolor on some jobsites where the pipe is tucked up inside of floor joists or in chase ways where traditional cooling by surrounding air is not present. Most equipment manufacturers use flue gas sensors to aid in protecting the vent system and U.S. Boiler is no different. Our control is set to kick in a Fan Rate Limiter when the flue gas temperature exceeds 192F and will activate a "Hard Lockout" if the temperature exceeds 204F.
    While I have seldom seen flue gas temperatures ever reach this point, I was on an Alpine installation where the contractor installed an Alpine to only generate DHW for a motel. The boiler operated fine last year but when he turned it on several weeks ago for the summer season, it kept locking out on the Flue Gas Sensor 204F limit even though the boiler temperature was only at 150F and struggling to rise. Combustion was correct, vent installation was correct, gas was correct and the heat exchanger was spotless. Upon asking the installer what changed between last year and this year he said nothing. That's when I asked what he does with the boiler and indirects during the winter. Answer was "I blew them all out with compressed air".

    Knowing that the Giananni heat exchanger headers are on top and the coils are suspended below, I made it clear to him that there is absolutely NO WAY that you can get all of the water out of that heat exchanger and that the water remaining in the bottom half of the coils had probably frozen and swelled the tubing. To prove this point I tried putting a credit card between the coils on the bottom of the heat exchanger, then the sides and top. It would not fit between the bottom coils but inserted easily in the upper areas. He effectively lost over a third of his heat exchanger surface area to conduct heat from the flue gasses thus the high flue gas temperatures and sluggish heat transfer.

    As for the incidents that do happen out there, we unfortunately have no control over how these boilers and venting are installed. Provided all guidelines and warnings are adhered to, the installation should not encounter any problems. I have been on many installations where chemicals (Pool Treatment and even Miracle Gro) have been in the area of the air intake and virtually disintegrated the swirl plate in the fan shroud. I would also be safe in saying that PVC exposed to chemicals in the surrounding air could also lead to degradation of the PVC as shown in a couple of the photos posted. I'd be interested in knowing what grade of PVC was used in the installations Mr. George was referencing.
  • Tim McElwain Tim McElwain @ 9:14 PM
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    Another Ron George article

    in Plumbing Engineer , May 2012 it can be found also
  • Ron George Ron George @ 5:32 PM
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    PVC Failure Article

    PVC flue pipe failure
    By Ron George,CPD,
    President, Ron George Design & Consulting Svcs.
    In the May 2011 issue of this magazine, I wrote a column titled, “Is PVC an acceptable vent material for flue gases?” in which I pointed out many problems and challenges associated with venting flue gases with polyvinyl chloride (PVC) pipe. In the March 2012 issue, a representative of the Air-Conditioning, Heating and Refrigeration Institute (AHRI) wrote a letter supporting the use of PVC pipe on behalf of their appliance manufacturer members that use PVC as an alternative to the stainless steel or high temperature plastic flue venting materials that are listed for use.
    AHRI is an advocate on behalf of their members; they lobby at all levels of government, including at model code hearings. AHRI’s government affairs staff works closely with congressional staff on legislation that impacts the industry. In this case, it appears that they were lobbying the readers of Plumbing Engineer on behalf of the manufacturers of fuel burning appliances such as water heaters, boilers and furnaces that are recommending use of PVC pipe for venting combustible gases.
    Some people have asked why I am making such a big deal over using PVC for venting combustion gases. I would love to tell them it is OK to use these materials, but health and safety trump saving a few bucks on pipe material.
    PVC flue pipe failures
    Recently, I received a call from someone on behalf of a woman who had suffered a serious debilitating illness. The caller said a plumber gave him a copy of the May 2011 article. The caller went over some of the comments that were addressed in the article and explained that a woman had become seriously ill and permanently disabled from what is believed to be exposure to the combustion gases from two failed PVC plastic flue vent pipes in her home.
    I was asked to inspect the installation. I photographed, took temperature recordings and used a multi-gas detector to take readings. The two PVC flue vents were connected to two water heaters that were piped together in the garage of a three-story townhome. The plumber had found that the flue pipes in separate joist spaces were completely separated and that what appeared to be carbon monoxide poisoning and oxygen deprivation may have caused the woman’s illness; she apparently has brain damage and is now permanently disabled.
    In exposed locations, the PVC pipe was tan colored; above the drywall and below the second floor decking in the area of the break, it was a very dark brown. Dark areas on the decking and floor joists indicated that high temperature flue gases had possibly cooked the sugars or sap in the wood to a dark caramel color. Apparently, the ambient air had a cooling effect on the pipe in exposed areas; that is why the exposed pipe was a lighter brown color. In the floor cavity, the temperature on both sides of the flue pipe wall was the flue gas temperature. Wherever the pipe was near a floor joist or near insulation, the piping appeared to be darker in color. This was probably because of the restriction of ambient air circulation for cooling.
    The pipe was brown and discolored in the vicinity of the two water heaters, and two yellowish fittings were cracked and completely separated. Testing the flue gases in this case revealed that flue gas temperatures after the dilution air was added was still much higher than the 160 F hot water temperature and far in excess of the temperature rating for PVC pipe. The water heater manufacturer's literature recommended the use of PVC pipe and made no mention of system design temperature limitations or installation requirements for the PVC flues with respect to the location in a concealed space or adjacent to insulation. It also did not list any temperature limitations for a maximum thermostat setting on the water heater for systems using PVC flues. The PVC flue pipe separations above the drywall ceiling allowed products of combustion, including carbon monoxide and water vapor, to vent under positive pressure into the house over several years. This caused excessive mold and water damage to the structure.
    There is not much data on discoloration of PVC pipe or on ambient air cooling requirements for PVC flue pipes. It appears that PVC flue pipes should not be located in concealed spaces such as the space between a ceiling and a floor deck, near insulation or floor joists or in wall cavities that have no ambient air cooling capability.
    There is no standard for PVC pipe for use as a flue material for combustion gases and there is no testing for these conditions.
    The discovery
    When the home was being sold, an inspector found significant water damage in the lower levels. A plumbing contractor opened the drywall ceiling on the lower floor and found the two completely separated PVC flue pipes pumping carbon monoxide and moisture into the home. There was black mold throughout the floor space and on the exterior walls, where the wood structure and siding was rotted. Copper plumbing pipes in the area were green with oxidation from exposure to the moisture. The broken PVC flue pipes caused the plumbing contractor to wonder whether the building occupants had experienced any symptoms of carbon monoxide poisoning. These symptoms include the following: headaches, dizziness, nausea, flu-like symptoms, fatigue, shortness of breath, impaired judgment, chest pain, confusion, depression, hallucinations, agitation, vomiting, abdominal pain, drowsiness, visual changes, fainting, seizures, memory and walking problems. Not knowing her condition, the plumber contacted the homeowner and asked whether she had experienced any of these symptoms.
    She was amazed to hear this, because he was describing many of the symptoms she had been experiencing for several years. These were the reasons she had to quit her job and move away. Moving away very likely saved her life.

    Interestingly, although the CO levels were elevated to dangerous levels, they were not high enough to trip a carbon monoxide alarm. The combustion gases that were venting into the floor space and coming up through a floor register into the living space had oxygen levels that dropped to well below 18 percent in some areas. Low oxygen levels combined with elevated CO levels can be a deadly combination and can lead to brain damage.
    Flue gas temperatures
    PVC pipe has a temperature limit of 140 F; most water heaters and boilers have thermostats that exceed this temperature. Furnaces can have flue temperatures well above 140 F when the air filters are dirty and the air flow drops off. The maximum temperature setting for residential water heaters is 160 F, for commercial water heaters it is 180 F and for boilers it is 200 F, all above the maximum recommended PVC temperature of 140 F. Boiler water temperatures are typically in the 180 to 200 degree range, because most HVAC hydronic heating coils are designed for these higher water temperatures in order to reduce the heating coil sizes and to reduce the gpm pumping requirements.
    Plumbing engineers typically design hot water systems to store hot water about 140 F in water heaters to minimize Legionella bacteria and other organic pathogen growth in the hot water tank. They typically use thermostatic mixing valves conforming to industry standards to reduce domestic hot water temperatures to safe delivery temperatures.
    If a fuel gas appliance was 100% efficient, the flue gas temperature would be the same temperature as the thermostat setting or fluid temperature in the water heater or boiler. Since 100% efficiency is not really possible, all flue gas temperatures will exceed the thermostat setting. So, if a water heater is set at 160 F and the thermostat allows the fluid temperature to overshoot the set point by about 10 degrees F plus or minus, the flue gas temperatures on a very efficient residential water heater would be higher than 170 F. This is consistent with the temperature readings I got.
    Water heater storage temperatures
    I serve on an industry committee that is developing guidelines for minimizing Legionella in building water systems. The committee includes representatives of ASHRAE, ASPE, water heater manufacturers, plumbing designers, CDC, EPA, several pathologists and microbiologists and many other experts. They have recently tentatively agreed that the minimum storage temperature for water heaters should be 140 F in order to make sure that all parts of the domestic hot water system are well above the ideal growth temperatures for Legionella. The committee is also looking at minimum hot water return temperatures above the ideal growth temperatures for legionella bacteria. When this standard is published, storage type water heaters will have minimum storage temperatures of 140 F or higher; flue gases are typically much hotter than the water temperature.
    Because of the excessive temperatures of flue gases, PVC pipe manufacturers do not recommend the use of their pipes for venting combustion gases and have the following temperature limits for piping materials:
    PVC Schedule 40 140 F
    ABS Schedule 40 160 F
    CPVC Copper Tube Size 180 F
    CPVC Schedule 80 200 F
    PolyPropylene High Temp 230 F
    Stainless Steel 1,000 F – 1,400 F
    Why PVC material?
    Water heater, boiler and furnace manufacturers have gone to great lengths to promote and use PVC plastic flue pipes in applications that exceed the temperature ratings of the product. They cannot use traditional galvanized flues because the condensation produced is pure water and very aggressive and would corrode or rust the flue in a very short time. When galvanized steel flues develop rust holes, people may start suffering from carbon monoxide poisoning. Manufacturers needed to come up with a flue material that would not corrode. Stainless steel flues are an option but, compared to galvanized steel or PVC plastic, they are very expensive. High-temperature plastic flues were used briefly in Canada but were recalled after a series of flue failures. In the beginning, flues were cobbled together out of whatever flue materials they could find and PVC was included even though it is not rated for the system temperatures commonly experienced in flues. Water heater and boiler manufacturers began listing the ASTM standard numbers for PVC DWV pipe and PVC water pipe as the material to use for venting their appliances.
    PVC pipe standards

    The ASTM standards, PVC Schedule 40 DWV Pipe & Fittings — ASTM D 1785 and ASTM D 2665 have language as follows:
    This standard specification does not include requirements for pipe and fittings intended to be used to vent combustion gases.

    The cost of PVC plastic pipe cost is a fraction of the cost of stainless steel. I am guessing that there was a meeting after the May 2011 article and that AHRI decided to defend the use of PVC plastic for venting combustible gases.

    The AHRI representative agreed that no U.S. PVC pipe manufacturer recommends use of their pipe for venting of combustible gases. He then goes on to mention that AHRI uses the ANSI Z21 series of standards for appliance testing as the basis for acceptance of PVC flue piping. These standards only test for deflection at 157 F, although he claimed that they test to 158 F. That is not the correct temperature for PVC piping.

    He states that the Z21 series of standards tests gas appliances for extreme conditions. According to him, the test involves setting the thermostat to the highest setting and flowing water continuously to keep the burner on. In this condition, enough water can be flushed through the water heater or boiler to keep the water temperatures low enough to keep the flue gases cooled and relatively low. The test does not allow real-world conditions in which commercial water heaters reach the shut-off temperature of 180 F.
    To be accurate, just enough hot water should be flowed to cause cold water to enter the bottom of the heater and cause the burner to come on; then the flow of water should be shut off until the burner shuts off. Repeating this step about five or six times would be the real-world extreme condition. Each time the water heater cycles, the hot water rises to the top of the heater; each consecutive cycle overheats the water in the top of the heater and, with each consecutive stacking cycle, the water temperature will be 5 to 10 degrees hotter. As the water temperature gets hotter, so does the flue temperature.

    The test does not test for long term thermal cycling of the PVC pipe where the pipe becomes discolored. The test does not address all of the things that can cause flue gas temperatures to rise — scale on the heating surfaces; dirty air filters; insulation, drywall or studs against the pipe in joist spaces; partially and fully blocked dilution air inlets; etc. I would like to see a manufacturer provide a copy of testing and certification for any fuel burning appliance with PVC pipe testing for these conditions.

    According to the AHRI representative, the ANSI Z21.10.1-2009, CSA 4.1-2009 Standard, Gas Water Heaters Volume I, Storage Water Heaters With Input Ratings Of 75,000 Btu Per Hour Or Less tests and approves PVC pipe for use in water heaters, but the standard only references PVC pipe deflection at 157 F. It does not address or require the appliance to shut off if the 140 F limit is reached. The only place that PVC is addressed is in Table XII, which gives the maximum allowable temperatures of typical nonmetallic vent material used in water heaters. There is no justification for the 157-degree temperature, which exceeds the piping manufacturer’s temperature rating. Table XII is as follows:

    There is no testing for a water heater, boiler or furnace that has a system set at the upper temperature settings with a build-up of scale on the heating surfaces or with a plugged air filter.
    Scale is an insulator

    Scale on heating surfaces and higher system water temperatures that increase scale production are not extreme cases but are normal conditions expected over the life of a water heater or boiler. The AHRI representative states in his letter that scale is not an insulator. I strongly disagree. Numerous documents, research reports and papers address the insulating effects of scale formation on the heat transfer surfaces and the waste of energy associated with scale on heating surfaces. The insulating effect of scale on water heater and boiler heating surfaces results in increased flue gas temperatures. Scale also causes a substantial waste of energy.

    Scale deposits occur when calcium, magnesium and silica, commonly found in most water supplies, get cooked onto the heating surface and form a continuous layer of material on the waterside of the water heater or boiler heat exchanger surfaces. Scale creates a problem because it typically possesses a thermal conductivity, an order of magnitude less than the corresponding value for bare steel. Even thin layers of scale serve as an effective insulator and retard heat transfer.

    The National Institute of Standards and Technology, Handbook 115, Supplement 1 addresses the loss of efficiency based on scale formation. On well-designed natural gas-fired systems, an excess air level of 10% is attainable. An often stated rule of thumb is that boiler efficiency can be increased by 1% for each 15% reduction in excess air or 40 F reduction in the stack gas temperature. The efficiency of the equipment decreases about one percent for every 1/64-inch layer of scale on the heating surface. The result is overheating of the water heater or boiler tube metal, tube failures and loss of energy efficiency, which is commonly diagnosed by an increase in flue gas temperature.

    Fuel consumption increases as scale deposits increase. Water heater or boiler output will be reduced as the scale builds up. The flue gas temperatures rise, and the burner stays on longer in order to transfer heat through the scale and the heating surface. Energy losses and increased flue gas temperatures are a function of scale thickness and composition.
    Where is the data?

    A flue pipe should not be allowed to fail and cause an injury or death from a normal system temperatures, location of a flue in a concealed space, or a normal build-up of scale on the heating surface. This is a serious life safety issue that the appliance manufacturers apparently would like to sweep under the carpet.

    At the ASHRAE show in Chicago, I asked every water heater and boiler manufacturer that was exhibiting PVC flues on their equipment to show me any testing data they might have that shows the PVC material was not going to exceed 140 F. Some looked at me like deer in the headlights, others rolled their eyes, and a few said they didn’t know and suggested I talk to “that guy over there.” The guy over there did not know either. A few said, “Yeah, everyone’s using PVC now, and I have never heard of a failure.” Not one manufacturer could produce any technical data or a report addressing the temperature limits that the fuel burning appliance manufacturers are required to have for non-metallic PVC flue materials. There are acceptable non-metallic flue materials such as high temperature polypropylene and new, high temperature plastics that have higher temperature ratings than PVC.

    The fuel-fired appliance manufacturers, in their quest to use PVC pipe as an inexpensive flue material, realized that no piping manufacturer was going to go out on a limb and certify their pipe for use as a flue gas material, so a proposal for a code change was submitted to the International Fuel Gas Code to allow an exception for the listing requirements for flue gas materials. The exception allows for non-metallic flue materials to not be required to be listed for the application if the manufacturer of the equipment certifies their equipment for use with non-metallic flue materials. They are claiming that they have a certification test, but the test that the AHRI representative cited does not test for the proper temperature limits for PVC pipe. I would be glad to show them how to set up a realistic test.
    No PVC flue pipe standard

    The AHRI representative went on to talk about dilution air being mixed with the flue gas temperatures. This dilution air is often drawn into the water heater through openings in a hood on top of the water heater. It is a function of the size of the combustion air fan which, in many cases, is located on the flue outlet so there can be a negative pressure zone on top of the water heater where dilution air can be drawn into the flue. The dilution air imposes an additional CFM demand on the unit that is not covered in the manufacturer’s installation data. There is rarely manufacturer’s data on what the fan CFM is and how that affects the combustion air requirements for the water heater or appliance. If there are two appliances located in the same closet and both rely on cooling air mixing with the combustion gases, where are the additional requirements for combustion air openings and dilution air requirements? If a closet or space is designed for only enough air for the combustion requirements, and the hood is drawing many times more cubic feet of air than the combustion air requirement from the same space, the burner can starve, and improper combustion can cause soot conditions that will increase flue temperatures. Improper airflow to the closet or room containing the high efficiency equipment can starve the dilution air ports reducing the cooling capability of the dilution air that is intended to help cool the combustion gases. High ambient air conditions can also cause ineffective cooling of the combustion gases.
    Require proof or reject PVC as a flue material

    Until any fuel burning appliance manufacturer can produce an independent engineering lab test report that shows that the appliance will shut down if the flue gas temperatures exceed 140 F, an engineer or the inspector has every right to reject the PVC flue materials as not being in compliance with the requirements for listed flue pipe materials in the International Fuel Gas Code.

    Fuel burning appliance manufacturers should change their installation literature to prohibit PVC pipe and fittings. They should require other more suitable high temperature non-metallic pipe materials or stainless steel flue materials. They should also address all of the thermal expansion, ambient cooling and stress cracking issues with non-metallic systems. A consensus standard for non-metallic flue venting systems is really needed now if they are going to continue to promote the PVC material.

    The manufacturers and AHRI have created an unsafe condition by lobbying for a material that is not suited for this application. They should issue a recall letter to every business and every homeowner that has PVC flue pipes installed on equipment designed for non-metallic flue pipes if the equipment does not have temperature sensors or limit switches in the discharge flue that shuts down the burner if the flue gas temperatures exceed 140 F.

    Data also needs to be published showing the dilution air requirements at the maximum possible ambient air conditions. Recent weather events in Southern states have shown that ambient air conditions can get close to 115 F or higher. With combustion gases close to 200 F, you would need a pretty big combustion air opening to bring in enough 115-degree cooling air to bring the temperature down to a safe level.
    The decision to use PVC pipe for venting flue gases is purely a monetary decision; it totally disregards public health and safety. The International Fuel Gas Code exemption for non-metallic flue pipe materials is not safe and, in my opinion, should be repealed as an emergency code change. I also feel that manufacturers should immediately discontinue recommending the use of PVC pipe for venting combustible gases.

    Ron George is president of Plumb-Tech Design and Consulting Services LLC. He has served as chairman of the International Residential Plumbing & Mechanical Code Committee. Visit [u][color=#0066cc][/color][/u], e-mail [u][color=#0066cc][email protected][/color][/u] or phone 734/755-1908.
  • Zman Zman @ 12:05 AM
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    Great subject!

    Tim, thanks for revisiting this one.
    How do you feel about polypro?
    I believe the failures reported are related to excessive temps.I also think if the boiler companies are going to spec PVC the should design the boiler to lock out if the flue temp gets to hot.
    I work with a building department not to far from Aspen, They have recently required pressure tests on all concealed plastic boiler venting. I think this is a good call.
    Has anyone tried putting polypro gasketed or flex under pressure?
  • icesailor icesailor @ 12:47 AM
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    PVC Venting:

    I recently did a service call where I had installed a Ruud PVP-50 LP water heater with 3" Sch 40 PVC pipe and venting. I installed it over 10 years ago. I noticed that the inside of the PVC was black. I put my analyzer in the exhaust to see how it was running. The numbers were OK except the stack temperature. It was over 600 degrees. The white pipe was all a dark tan color.
    But it's OK.
  • Jason Jason @ 7:22 AM
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    600f stack temp brings two questions to mind. One how is this appliance efficient with that kind of vent temp? If it is designed to vent with PVC there is something wrong. Dirty & requires service? Mod/cons normally shut down under 250f.
    Second question is it safe? Tan pipe usually is very brittle and at 600f is it safe?
  • Henry Henry @ 9:00 AM
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    Article on PVC

    I read with much interest the article on PVC venting. The writer is very much uninformed on PVC Venting and the standards used for various materials. The 140F that he mentions is for PVC "PRESSURE" rating. IE, at 140F the pipe can support 75 PSI. All the temperature ratings mentioned are for temp/pressure ratings. BTW, ABS pipe only starts to deform at 217F which is superior to PVC.
    He also mentions that there are no standards or test procedures for plastic pipe venting. This is false. There is a UL standard called ULC636!
    Nearly all failures that we have seen, have been caused by the installer and NOT the pipe. In the other cases, the equipment failed. BTW 600F stack temperature would melt completly the PVC pipe! Cracked fittings are caused by the lack of space for the pipe to expand. At one point our company was using $100K a month of AL29-4C venting material. We have had more problem with this material than any other combined!

    The manufacturers have tested all sorts of venting situations before certifying an apliance to use a particular special venting system. We in the code sector ensure that the installations are safe for the user and continuously monitor what is happening  across all of North America to keep it that way.
  • Steamhead Steamhead @ 9:13 AM
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    Henry, that's a Canadian standard

    which does not have any force in the States.

    Currently, there is no standard here, and the various PVC pipe makers specifically state their pipe is not intended for use in venting combustion products, and is not listed for this use. 

    For now, the pipe manufacturers probably won't seek to have their product listed for combustion venting. Why should they? They get to sell the stuff, without incurring any liability.
    "Reducing our country's energy consumption, one system at a time"

    Steam, Vapor & Hot-Water Heating Specialists

    Oil & Gas Burner Service

    Baltimore, MD (USA) and consulting anywhere.
  • Mark Eatherton Mark Eatherton @ 9:49 AM
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    I guarantee you that Mr George will be coming by to see the responses of The Wall. My questions are;

    1. It sounds as if the actual failure was possibly stress induced due to the high coefficients of expansion common to PVC plastic? If yes, would an expansion joint have alleviated this stress and avoided pipe/fitting failure?

    2. Was the appliance doing only DHW, or was it also doing space heating and DHW?

    3. What is the status of your patent pending flue temperature control device?

    4. Why no mention of ABS in your articles?

    5. Are you aware that long term exposure to Black Mold will also produce many of the symptoms that the resident of this home has experienced?

    6. If you feel that the Lignin had been cooked out of the wood due to the close proximity of the PVC to wood, what do you think the chances of pyrolysis would have been at an elevated wall surface temperature associated with highly conductive, low thermal resistance stainless steel would have been?

    Lastly, as an expert witness, do you think it ethical to bring this situation before the public prior to finalization of any potential litigation being closed out? You know, there are a LOT of legal beagles who frequent this site...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Ron George Ron George @ 1:27 PM
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    Reply to Mark E.

    Mark E. Wrote:  1. It sounds as if the actual failure was possibly stress induced due to the high coefficients of expansion common to PVC plastic? If yes, would an expansion joint have alleviated this stress and avoided pipe/fitting failure?
    Ron's reply: The pipe was not restrained.  There is no PVC pipe or PVC expansion joint listed or approved for venting combustion gasses.

    2. Was the appliance doing only DHW, or was it also doing space heating and DHW?
    Ron's reply: Boiler manufacturers, water heater manufacturers, furnace manufacturers and manufacturers of equipment intended for both space heating and domesti water heating all have literature recommending the use of PVC materials for the flues.  The thermostats on all these appliances allow discharge flue temperatures which are above the allowable temperature limit of 140 established by the PVC pipe manufacturers.
    3. What is the status of your patent pending flue temperature control device?

    Ron's reply:  I let it lapse.  No patent.  This is a safety issue not a monetary issue.

    4. Why no mention of ABS in your articles? 
    Ron's reply: No reason.  ABS has a temperature limit of 180 F.  !80 may still be questionable is many applications where the temperatures can easily exceed 180 F with scale build-up on the heating surfaces.

    5. Are you aware that long term exposure to Black Mold will also produce many of the symptoms that the resident of this home has experienced?
    Ron's Reply:  In this case it is clear the black mold was caused by the failed PVC flue pumping warm moist air and combustion gasses into the joist space.  What is your point other than to defend the use of PVC for venting combustion gasses. PVC is an inapropriate material for this application and the underlying reason is to save a couple of bucks?  In either case a person can become very sick or die because of a failed PVC flue pipe.

    6. If you feel that the Lignin had been cooked out of the wood due to the close proximity of the PVC to wood, what do you think the chances of pyrolysis would have been at an elevated wall surface temperature associated with highly conductive, low thermal resistance stainless steel would have been?
    Ron's Reply: The stainless steel is a double wall system so your comments about radiation are irrelevant.  The flue gasses were directly impenging on the wood with convection currents from the broken PVC flues.  In a double wall stainless steel flue system with proper clearances or with a properly designed and listed non-metallic flue system the external temperatures should not get high enough to cook the sap out of the wood. 

    Lastly, as an expert witness, do you think it ethical to bring this situation before the public prior to finalization of any potential litigation being closed out? You know, there are a LOT of legal beagles who frequent this site...
    Ron's reply:  I have not disclosed an address or names.  I have been speaking in generic terms.  This is a serious life safety issue that people need to be made aware of.  Safety is always my first concern.  Safety should always be more important than saving a few bucks on a material that is not intended or listed for an application.
  • JohnHenry JohnHenry @ 10:04 PM
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    Mr. George,

    Having been trained as a mechanical engineer, I'm not feeling real warm and fuzzy about your comments here. You seem to imply that the engineers who design and test these systems have little regard for the safety of consumers. Nothing could be further from the truth. Engineers care very much for the consumer and are generally insistent that the systems they design are pretty much bulletproof.

    While I applaud your apparent desire that all heating systems be immune from reckless and unqualified installers, zero maintenance and general neglect, in the real world that's just not going to happen. One of my favorite sayings is: "if you build a better idiot trap, they'll build a better idiot".

    When a company designs, manufactures and sells a system, they have the right to expect proper and competent installation of their product. Indeed the literature that invariably comes with said products states that it must be installed correctly.

    Like it or not, cost does matter. If you can get adequate performance from a cheaper material, you use it. Period. That's just the way it is. EVERYTHING has a cost benefit analysis attached to it, from how much you spend on flowers when you piss off the wife to what material you're going to use to vent a combustion appliance and everything in between. Would you ballast a sailboat with gold?

    Let's get to the PVC, shall we?

    ASTM Type-1 PVC standardizes schedule 40/80 PVC with:
    a melting point of 360*F
    a continuous service ambient air temperature rating of 160*F @ 264psi (temperature rating goes up with less pressure)
    a deflection temperature of 154*F @ 264psi (temperature rating goes up with less pressure)
    a Rockwell hardness of 112

    That's a very simplified example of the type of data an engineer looks at when choosing material to approve for venting. The engineer will use temp/strength curves to determine the maximum temp a material can take before it deforms in the use and layout it's installed in (in this case probably 1 in WC pressure, laying horizontal with support every 5 ft). They then see if that temp is within the bounds of the intended operating range (with a generous factor of safety of course) of the application.

    My particular condensing appliance allows a maximum 149*F flue temp before it shuts down. My system return water has never run above 120*F. I've never measured the outside temperature of my flue to be more than 105*F. Given these running parameters, the PVC that I carefully and correctly installed will probably never leak, corrode, give off fumes or genarally cause me any trouble. How is that not the right vent material for me?

    There are vast numbers of condensing hot water heaters/boilers running PVC venting without any venting issues. It seems that PVC can indeed be an appropriate venting material.
    The bitterness of poor quality remains long after the sweetness of low price is forgotten.
  • zacmobile zacmobile @ 3:36 PM
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    PP venting

    I find it curious he makes no mention at the end of the article of the various PP venting products that are available, I can't understand why everyone doesn't switch over to this in light of all the controversy surrounding PVC. I certainly have, it's only a little more costly than PVC, waaay cheaper than CPVC and outperforms either of them without the yummy solvents.
  • Henry Henry @ 8:25 PM
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    Actually, it is a North American standard! Just that nobody wants to spend the money to relabel the pipe as S636 because in the US there is no need! There is "no force" as NFPA54 does not require it. The members of NFPA 54 recognise that using the existing various plastic pipes IF installed properly pose no danger to the user. You are right about US pipe manufacturers CYA. They claim that it is not a suitable use so as not to have any liability for incorrect installations and failures. They don't have to pay for certification or relabeling!

    Mark, there are no expansion joints available. The installer must take into consideration the expansion of the pipe while installing. If memory serves me right, PVC will expand 4 inches over 100 feet at 70 F rise. The lowest plastic was ABS 1 inch! I have all the expansion rates in my office. I have seen busted fittings due to expansion and incorrect installs!
    I have checked my own home PVC vent after 10 years. There was a slight brown discoloration most probably due to Chloride removal. This is something I have seen in an aquatic lab when the numb-nut ING specified sch 80 PVC for a pure water aquatics lab. If the vent was cracked, it sent warm humid air on the wood creating spores and mould for who knows how long. I am sure that no preventative maintenance was done according to the certified manufacturers instructions.

    As among other things, a forensic investigator for insurance companies, an expert witness in litigation and a voting member of the National Gas Code and 7 sub-committees, I find Mr George's motive to publish such an inaccurate article as having perhaps personal motives! I am sure that some legal buzzard will use his article to crucifix someone without all the expertise to defend himself! It is very shameful.
  • Steamhead Steamhead @ 9:05 PM
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    The lawyers are already doing that

    I believe in the Lofgren case in Colorado (which is the one we've heard the most about), the pipe manufacturers were sued, but they were able to document that their PVC was not, and never was, listed for venting combustion products. So they were told they could go home. 

    Things really are different south of the border, Henry. Our Codes require the stuff to be listed, same as yours, but it probably never will be until the listing requirement is strictly enforced.
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  • ChrisJ ChrisJ @ 1:21 PM
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    power vented tank heaters

    As a homeowner and not a pro I may be over my head on this but I'm assuming this issue also includes tank water heaters which are power vented.  I have to assume so being it has a burner and can obviously have a failure which would increase temperatures.

    Last fall I installed a Bradford & white heater which of course recommended PVC.  My point would be the PVC connects to the heater via a soft rubber adapter which connects to an ABS plastic blower. I don't know what the rubber adapter is made from but its not silicone.  They also supply a outside partial elbow which has a wire mesh screen in it which is molded out of white PVC.  I don't know about others but I would feel a bit stupid connecting stainless pipe to an ABS housing using a rubber adapter.  The outside screen would be another issue as your obviously not going to glue the supplied one onto stainless.
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  • Ron George Ron George @ 4:44 PM
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    The right material.

    I tested a water heater recently with a black plastic collector on the top and it had an external temperature of 188 F (downstream of the dillution air inlets) using an IR temperature sensor.  The internal temperature was probably much higher.  When a water heater heating surface fouls with scale the flue gas temperatures will increase significantly.  A burner shut-off using a flue gas temperature sensor that is rated for the flue materials is needed for non-metallic flues.   PVC flues should not be allowed because most appliance or equipment T-stats exceed the material temperature rating.
  • VictoriaEnergy VictoriaEnergy @ 3:08 AM
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    PVC can work fine

    The simple answers are: 1) All appliances using a plastic vent system, and/or, an uninsulated vent system with low or zero clearance to combustibles, must include a manual reset high limit switch in the vent outlet.  2) Adopt a similar, if not parallel standard to ULC636 which clearly establish the maximum continuous and intermittent peak temps the material has to tolerate.

    Our company has been installing PVC venting on warm air furnaces since 1993.  This material has worked well on furnaces.  Not surprising since the flue temps are often in the 100~120F range.  All of the old equipment I can think of had a thermal limit switch mounted in the outlet of the inducer.  Much of the newer equipment seems to have eliminated the switch (tisk tisk).  We inspect PVC closely on every service call and the odd issue we've seen appear are in joints that have no evidence of primer being used in them before cementing.

    I think the room air flue temp dilution design is problematic, and the HWH manufacturers would have to walk away from the design if the were mandated to comply with the above.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
  • Limamikemike Limamikemike @ 1:14 PM
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    Came across this:

    Basically says No PVC on anything other than forced air furnaces vents-dated march 8/2012 in canada. Interestingly it says this directive OVERIDES manufacturers instructions.

    I recently installed a Lochinvar WHN110 with B11A PVC vent material in a low to mid temp app, the Lochinvar manual states ULC-S636 in canada, either PVC or CPVC so long as its ULC cert. Also the wall thimble included with the boiler is made from ULC-S636 B11A -65c material.

    In your eduated opinions should I recall and change it? It passed inspection as is on April 27/2012.

    ULC-S636 BIIA -65c flue PVC-White pipe

    ULC-S636 BIIB -90c flue CPVC-Grey pipe.
    This post was edited by an admin on May 24, 2012 1:15 PM.
  • VictoriaEnergy VictoriaEnergy @ 4:09 PM
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    Responding to the directive

    It looks like your situation is a good example of the issue the inspection authority is having a problem with.  The instructions for the boiler accept the use PVC,  The B11A-65C is certified for operating temp of 149deg F(65 deg Celsius), but the manual states :

    The control module monitors the flue temperature by a sensor located in the flue exhaust. If the flue temperature exceeds 215°F the control will reduce the maximum fan speed. If the flue temperature exceeds 240°F the control will shut the unit down. The unit will restart automatically once the flue temperature drops 25°F and the minimum off time has expired.

    So although your system is probably running flue temps well below the limit of the vent today, what happens in a few years if the unit is not maintained the hx gets scaled up full of crud, and the flue temps creep up?  If you have indirect HW on the system, it’s reasonable to see the boiler frequently overheating the vent.
    As far as your customer goes, (assuming the notice is for your area) I think you have to contact them and advise the installation needs to be upgraded.  They won’t have an issue with you tell them they need a new vent, but they likely will want to talk alot about who gets to pay for it.

      If you started the job before the directive was issued, you’ve done nothing wrong.  The upgrade materials and labor are chargeable.  I’d send them a copy of the directive, the phone # of the inspector, and tell them they are not obliged to have your company do the upgrade, but they must have it upgraded.  Out of sympathy and in the interest of good customer service, I would offer it to them at my cost if they were willing to do the upgrade during the summer when my work load was minimal.
    If you remember the job well enough, you can include a complete quote for the fix.  If you have previously delt with them via e-mail, I’d 1st communicate that way.  Wait a week and contact them again.  If they refuse to take action, claim to be hiring another gas fitter for the work, or won’t communicate further, forward all the info to the gas inspector to show him you tried and won’t be taking further action.
    Home Owners Please Note:

    You are receiving advice from some very skilled pros completely free of charge. One of the reasons I participate is to sharpen my own troubleshooting skills. So; did we get it right? I would be grateful if you extend this courtesy back by posting the final outcome of the issue you are inquiring about. Thanks
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