The Wall
Forum / Gas Heating / Gas piping
  • Post a Reply to this Thread

    Gas piping (45 Posts)

  • RobG RobG @ 2:56 PM
    Contact this user

    Gas piping

    Tim, A previous post got me curious so I went to Navian's website to investigate. Here is their claim:

    Better Adaptability to Gas Systems
    The Negative Pressure Gas Valve and Fan with Dual Venturi operation allows for better adaptability to low gas pressure applications. This industry leading technology makes it possible for the NPE to be installed with 1/2" Gas Lines up to 24'.
    Easy residential tank replacements.

    Maybe if the unit was mounted a foot away from the meter and had no fittings.
    Or am I missing something about their "Negative Pressure Gas Valve and Fan with Dual Venturi" that defies everything that I have ever learned about sizing gas piping.

    Please explain.

    Thanks,
    Rob
  • icesailor icesailor @ 4:25 PM
    Contact this user

    The Word.

    Tim will have The Word.
    I have a question. Who resolves the dispute between you and the inspector when he objects to piping the boiler with 24' of developed length of 1/2" black pipe for that particular boiler? Most inspectors said NO and they didn't care what it said in the manual or sales brochure. At least that's what AHJ's I've dealt with said. "What does the appropriate table in the code book say? Does it say that you can pipe 24' developed with that BTU inlet with that system pressure? If it isn't in the tables, make it in the tables or "I ain't gonna sign it off unless I get a letter from The Board saying it is OK." In my old world.
  • Tim McElwain Tim McElwain @ 5:25 PM
    Contact this user

    Funny you should ask

    When I read that I made a note to myself to look into that with the manufacturer. There is nothing that I know of with a negative pressure valve that allows it to have any less gas at the inlet than any other valve. If you have insufficient pressure you have less gas therefore you can not meet BTU demand. Fan with dual venturi only means that when you have higher demand 199,000 you use a different venture in addition to the primary venturi. Still does not change the requirement for sufficient pressure based on specific gravity, pipe size and allowable loss, those things do not change.
  • Tim McElwain Tim McElwain @ 5:41 PM
    Contact this user

    Rob I just sent of an inquiry to

    the folks at Navien lets see what they have to say.
  • Ironman Ironman @ 6:43 PM
    Contact this user

    Tim

    I couldn't agree more. If a cubic ft of gas has a caloric value of 1050 btu's, then that's all you're gonna get no matter what you do in the appliance. The chart that I just peeked at says you'll get 110 cubic feet through a 1/2" line that's 24' long. That looks like about 115,500 btu's to me.

    Someone's doing funny math again.
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
  • SWEI SWEI @ 11:49 PM
    Contact this user

    Not speaking for Navien here

    but based on conversations with engineers at tankless manufacturers, I suspect this may be a case of marketing spin applied to what I believe to be a very reasonable engineering decision:  In the event that gas pressure drops, reduce the firing rate until gas pressure stabilizes (as opposed to throwing an error and shutting down altogether.)

    Current codes do not take this behavior into account.
    This post was edited by an admin on March 20, 2014 11:51 PM.
  • Snowmelt Snowmelt @ 9:02 AM
    Contact this user

    My understanding

    From my understanding, you still have to follow the code book to getting two the appliance in other words you can't have 600,000 btu going 40' on 3/4' pipe you wil still need 1-1/4' but let's just say the last 15 feet had 1/2' piping, With the neg. gas valve, it will suck or pull the gas into the machine rather then the natural flow. Also the last two threads were right, there's no error code for not enough gas to keep up with water temp.
    I also was watching a video where they actually used 40" of 1/2 pipe and the machines was going down real low on gas with the monono meter and still kepping up with the water temp.
    I experienced the opposite in the past where there was not enough black pipe volume to equal the btu's needed and you can actually see the gas pressure go down and the water temp fluctuate.
  • icesailor icesailor @ 9:37 AM
    Contact this user

    Understanding(?)

    I don't know any answers.
    I went to a 2 day class at Viessmann in RI on Vitodens boilers. The question was asked by someone from New York city that where he worked, there was an area that had low pressure gas in the whole system and they didn't use regulators. That the whole system was (say) .5". What happens to the Viessmann gas valve when it sees gas at lower pressures? The instructor answered that the gas valve/computer adjusted for the lower pressure but because of the lesser pressure, the computer couldn't correct for gas pressures under .4". The burner would stay running, the output would drop. If what I understood, isn't that the same idea of the Navien valve? That it adjusts to keep the burner running, even at lower than standard pressures, just the output drops.
    Forgive me if my decimals are off. The concepts are there.
  • Tim McElwain Tim McElwain @ 11:57 AM
    Contact this user

    Negative pressure gas valves do not suck in

    gas. The gas pressure at the inlet to the gas valve must be the same as for any gas valve. The combustion air blower is what controls how much gas is going to go into the burner and eventually into the combustion chamber. If the gas pressure is reduced below 5" W.C. (typically what most equipment manufacturers call minimum inlet pressure) then the outlet pressure and  ultimately the amount of BTU required will be reduced somewhat. The combustion air blower is typically controlled by the ODR so all it does is ramp to the required speed to cause the burner to fire at the desired rate for that speed (based typically on a 5 to 1 turn-down ratio on residential equipment). If the gas pressure is not there even though the demand for gas is the system will have reduced input and not be able to satisfy the required BTU to meet the heat loss. In some cases if the input is below the low end of that ratio it may affect the flame sensing and you would have burner shut down due to insufficient microamps being available

    The Vitodends 200 with Lambda Pro sensing is much more forgiving but it also will eventually be affected by low input.

    Burner design has a lot to do with its ability to operate at low pressure and still have sufficient port loading and inspiration to stay lit.

    The point of claims by manufacturers that equipment will fire at lower inputs is nothing new. I have seen atmospheric burners with thermocouples operate with pressures at the inlet of the gas valve as low as 2" W.C.. As long as the pilot (mercury, bi-metal or thermocouple)  could sustain enough pressure the pilot would stay lit. Pilots by the way on regular gas valves is not regulated it is on whatever the line pressure is to the equipment. Those burners however at the lower pressure could not deliver enough BTU to satisfy heat loss, but did give some heat. the thermostat set at 70 would only get to 65 so the customer calls in a not enough heat call. This is also why it is important to do heat loss and fire the equipment at its maximum designed firing rate based on the OUTPUT matching heat loss. Systems that use microamps to prove flame are much more sensitive than the old pilots and are more susceptible to failure at low gas pressures.

    Manufacturers have to deal with the fact that some inner city low pressure systems with cast iron mains may not always have the typical 6" to 10" W.C. pressure they normally have. A word of warning to the installer/contractor you better make sure before you sell that high end product that requires minimum pressures of say 5" W.C. that the area in which you are going to install it always has that pressure available. If not it may show up as a no heat call on the coldest day of the year when demand is at its maximum. This year in some areas that has been quite often.

    In the case of the on demand water heaters such as the Navien at 199,000 BTU demand for top draw you may have cold water in the shower.
    This post was edited by an admin on March 24, 2014 9:45 PM.
  • RobG RobG @ 4:59 PM
    Contact this user

    Tim

    Tim, have you heard back from Navian? It will be interesting to see how (if) they say they do it.
    I agree, someones doing fuzzy math. (that's why I said only if the unit was mounted one foot away from the meter). It's interesting what the (no ofense intended) typicaly Japanese manufacturers will claim to sell their product, and how many people beleive them. At several training classes I have been told how if you turn up the tankless temp and mix it down, you will get more hot water, WTF? A BTU is and will always be a BTU. That will work with an indirect or tank type water heater, but not a tankless.

    JMHO,
    Rob
  • Tim McElwain Tim McElwain @ 6:04 PM
    Contact this user

    They acknowledged my inquiry

    but stated they were taking my question under advisement.
  • Ironman Ironman @ 7:31 PM
    Contact this user

    Interesting

    "Under advisement". Whatever that means.

    I have been in Navien training class where less than stellar attendees have ask why a199k btu appliance could not be connected to a 1/2" gas line. After the instructor gave a detailed and correct explanation, the knucklehead replied: "You ought to make that thing where it can be hooked to a 1/2" line". The instructor then explained again why it could not be done and the knucklehead said: "Well, I don't know about any of that stuff, but you ought to make that thing where it will work with a 1/2" line".

    I think someone at Navien has realized that they sell to a lot of knuckleheads and therefore they're gonna "tell 'um what they wanna hear".
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
    This post was edited by an admin on March 21, 2014 7:34 PM.
  • icesailor icesailor @ 9:43 PM
    Contact this user

    Knuckleheads:

    Now is the time that Steamhead comes in and says
    YOU CAN'T FIX STUPID!!!!
    But if he isn't already in business, he will be shortly. With the belief that "Profit is an obscene concept" and "Overhead is a Ceiling".
    Everyone is a crook except him, and he is always the low bidder that drives a beater truck and works for cash only. If he is one of 6 companies price a job, 5 will be $11,500 to $12,500. He will be $5,000. Because he knows how to save money. Met a lot of them. Inspectors love them. If they can ever find them.
  • bob eck bob eck @ 4:31 PM
    Contact this user

    1/2" gas piping

    Tim please let us know what answer Navien comes up with.
  • Tim McElwain Tim McElwain @ 6:37 PM
    Contact this user

    Will do Bob,

    I am still waiting they will probably get back to me on Monday, I hope. If not I will call them.
  • Snowmelt Snowmelt @ 10:30 PM
    Contact this user

    Navien

    I'm sending my two workers to the navien class this week I also have to call the tech/teacher on the phone, how do you want me to say the question about the 1/2 gas line?
  • 4Johnpipe 4Johnpipe @ 8:43 PM
    Contact this user

    Gas Sizing

    I use the series summation method for gas pipe sizing. The 1/2" gas pipe (iron) has a .067" water column pressure drop per foot. By most standard the gas utility supplies 8" of WC with a .5" drop through the regulator. That gives a starting point of 7.5" WC. Navien uses 24' as a guide. If you multiply .067"WC by the footage of 24' it would read 24' x .067" WC= 1.608" WC drop in that section. Take the 7.5" - 1.608"WC = 5.892"WC at the end of the run. You need to know the total of BTU's connecting to the pipe to be accurate.
  • Tim McElwain Tim McElwain @ 9:12 PM
    Contact this user

    4 john pipe are you an

    engineer? Were do I find the Series Summation Method of pipe sizing? My code book NFPA 54 / ANSI Z223.1 and also the International Fuel Gas Code allows the following pipe sizing methods:
    1. The Longest Run Method
    2. Branch Length Method
    3. Hybrid Pressure Method
  • 4Johnpipe 4Johnpipe @ 9:25 PM
    Contact this user

    Sizing

    Tim I found the method about 12 years ago in Gastite's sizing tables in their manual. The gas code only suggests 3 methods. I am also an HHS, ICS, Subcode and Construction official. The sizing method in Gastites manual is approved by the CSA which is a recognized engineering and testing facility for all codes. The code you referenced also states it is the designers choice. We are the designers. Another section in the beginning of the code states we are to minimize the hazardous / flammable material inside of the building. Sizing gas pipe correctly reduces the size and achieves this statement. Are you in NJ? If so Tom Pitcherello is fully aware and endorsed all of the documents I sent him years ago. He actually made a code clarification in the code communicator a few years back for exactly this situation.
    PS this method is really just a more accurate branch length method. It obtained the water column per foot using that formula that is in the IFGC.
    This post was edited by an admin on March 24, 2014 9:30 PM.
  • Tim McElwain Tim McElwain @ 9:44 PM
    Contact this user

    My Gastite Manual is at my training center

    so I can not determine if you are correct. Is the table for sizing Gastite CSST or is it also for black pipe?

    No I am not in NJ but in Rhode Island.

    Do you feel this is how Navien is determining the use of 1/2" pipe for their 199,000 BTU on demand water heater?

    My personal experience as a service technician and also an instructor on gas for 50 years finds that the use of 1/2" pipe becomes a real problem in the inner city areas of the Northeast which typically are supplying between 6" W.C. to 10" W.C. in their mains on a good day. This past winter we have been seeing pressures of less than 5" W.C. on a pretty steady basis. I took a stand as the head of the service department in a gas utility here in the NE to have a minimum pipe size in those areas to heating furnaces, boilers and on demand water heaters of no less than 1" pipe. This is even more needed now with Modulating/Condensing equipment.

     The code you referenced also states it is the designers choice. We are the designers. I understand that and am aware of the code allowing for other designs as long as they get the job done.

    Would be interested to hear how you feel about this.
  • heatpro02920 heatpro02920 @ 10:07 PM
    Contact this user

    Tim I am interested to see what Navian has to say

    I am not pro Navian, I have thrown away my share of that thing they call a "combi boiler" most before warranties were up, just not worth fixing any further, the customer still has to come up with the service fee and go a week with no heat when you are waiting for a HX... Someone here is installing them like crazy, we just priced a job for an excellence and the home owner called and said they found someone to do the job for 1/3rd of our cost!!! I was shocked since the materials cost more than that... Turned out they got a Navian, its all hung but the contractor is waiting to hook it in until the winter is over so the customer doesn't have to go without heat....
  • 4Johnpipe 4Johnpipe @ 10:12 PM
    Contact this user

    Sizing

    The Gastite manual has per foot tables for iron pipe and their csst. It has been extremely helpful over the years. I have even been asked to teach the sizing to several building departments and trade organizations. It is simple math plug and chug stuff. You can also go on line to get the tables...
    This post was edited by an admin on March 24, 2014 10:13 PM.
  • 4Johnpipe 4Johnpipe @ 10:18 PM
    Contact this user

    Tables

    Tim here you go...Wont attach sorry...
    This post was edited by an admin on March 24, 2014 10:20 PM.
  • RobG RobG @ 2:45 PM
    Contact this user

    Sizing

    According to the charts in the Gastite manual that I will try to attach, the only way that you could do 24 feet of 1/2" piping (or equivalent length) might be to find a 6" pressure drop acceptable. In my neck of the woods the inspector would laugh at me if I tried to use that as an example. I'll stick with the .5" pressure drop tables.

    http://www.gastite.com/downloads/pdfs/gastite_sizing_tables_natural_gas.pdf

    Rob 
  • Tim McElwain Tim McElwain @ 4:49 PM
    Contact this user

    Both the state and the

    local utility here want an allowable pressure drop of 0.3" W.C., that will give the largest pipe size but sure cuts down on poor pressure problems in the dead of winter.

    I really have to sit down with the charts and look at them as I only really look at them when I teach CSST (not very often).
  • Tim McElwain Tim McElwain @ 7:08 PM
    Contact this user

    Sorry nothing from Navien

    I also called and left a message so maybe tomorrow.
  • 4Johnpipe 4Johnpipe @ 9:18 PM
    Contact this user

    Definition

    “Allowable Pressure Drop:  The design pressure loss on any piping system under maximum probable
    flow conditions, from point of delivery to the inlet connection of the equipment, shall be such that the
    supply pressure at the equipment is greater than the minimum pressure required for proper equipment
    operation.” The state or the utility can not tell you "the designer" what pressure drop to use. The pressure drop is the difference between delivered gas pressure at the house side of the gas meter and the required pressure of the equipment or appliance. If we have 8" of water column and the unit requires 5" of water column we have 3" of water column to play with. On another note if you supply a furnace with say 7" of water column...the gas valve will consume or burn all the gas...The problem is the heat exchanger is designed to extract the heat at the rated requirement most of which is less than 5" of water column. The rest of the heat is simply going up the chimney. This goes across the board even with negative pressure combustion chambers.
    This post was edited by an admin on March 26, 2014 9:24 PM.
  • Tim McElwain Tim McElwain @ 6:51 PM
    Contact this user

    Let me look at what you posted

    Definition“Allowable Pressure Drop:  The design pressure loss on any piping system under maximum probable flow conditions, from point of delivery to the inlet connection of the equipment, shall be such that the supply pressure at the equipment is greater than the minimum pressure required for proper equipment
    operation.”  YES THAT IS TAKEN DIRECTLY FROM NFPA 54 5.4.4.


    The state or the utility can not tell you "the designer" what pressure drop to use. THIS CAME ABOUT HERE IN RI DUE TO PROBLEMS WITH PRESSURE PROBLEMS IN THE EXTREME WINTER MONTHS ON THE LOW PRESSURE CAST IRON MAIN SYSTEMS. THE STATE (MECHANICAL DIVISION) DETERMINED THAT THE SAFEST WAY TO HANDLE THIS WAS TO USE 0.3 " W.C. AS THE ALLOWABLE. THAT CREATED THE LARGER  PIPE SIZE TO THE EQUIPMENT TO HOPEFULLY ALLOW FOR SOME DROP IN PRESSURE  IN THOSE EXTREME TIMES. THE LOCAL UTILITY AGREED THIS WAS AN ADEQUATE SOLUTION UNTIL NEW PIPING SYSTEMS COULD BE INSTALLED WITH POUNDS PRESSURE.


    The pressure drop is the difference between delivered gas pressure at the house side of the gas meter and the required pressure of the equipment or appliance. If we have 8" of water column and the unit requires 5" of water column we have 3" of water column to play with.WHY PLAY WITH IT INSURE ADEQUATE PRESSURE AT FULL 8" W.C. IS AVAILABLE AT THE INLET TO THE GAS VALVE 


    On another note if you supply a furnace with say 7" of water column...the gas valve will consume or burn all the gas. NOT TRUE.THE GAS VALVE HAS A BUILT IN REGULATOR WHICH REDUCES THE GAS PRESSURE TO TYPICALLY 3.5" W.C. AND AS LONG AS THE ORIFICES ARE SIZED CORRECTLY THE FURNACE WILL ONLY BURN WHAT THAT PRESSURE 3.5" W.C. AND THOSE ORIFICES ALLOW, NO MORE NO LESS.


    The problem is the heat exchanger is designed to extract the heat at the rated requirement most of which is less than 5" of water column. The rest of the heat is simply going up the chimney. This goes across the board even with negative pressure combustion chambers. WHAT IS LOST UP THE CHIMNEY HAS TO DO WITH EXCESS AIR, INPUT, TEMPERATURE DIFFERENCE IN THE FL;UE AND THE HEIGHT OF THE FLUE OR CHIMNEY ESPECIALLY ON ATMOSPHERIC BURNERS WHICH HOPEFULLY ALL ARE NEGATIVE PRESSURE IN THE CHAMBER AND IN THE FLUE.IF YOUR REFERENCE TO NEGATIVE CHAMBERS WAS MEANT TO BE DIRECTED AT MODULATING CONDENSING EQUIPMENT THEN THE CHAMBER IS NOT NEGATIVE BUT POSITIVE. THE EQUIPMENT USES A NEGATIVE PRESSURE GAS VALVE WHICH MUST HAVE ADEQUATE PRESSURE AT ITS INLET TO ALLOW FOR LET US SAY A 5 TO 1 TURNDOWN RATIO. SO WE HAVE VERY LITTLE IF ANY DROP IN PRESSURE FROM THE LOW END (LOW FIRE) TO THE HIGH END (HIGH FIRE).This brings us back to the Navien at 199,000 BTU's I can't agree with using your summation method on that equipment in my area of the country especially in the inner city low pressure areas.By the way I looked up the method in the Gastite manual I have at the center and realized that I do teach it especially with CSST using a 2 pounds or 5 pounds feed to a Maxitrol manifold dropping down into the equipment in close proximity to the equipment.
    This post was edited by an admin on March 28, 2014 5:46 PM.
  • 4Johnpipe 4Johnpipe @ 9:51 PM
    Contact this user

    Pressure

    Tim you have a difficult situation to deal with it sounds like...We have sections (very few) that have bad pressure. Some parts of town have such low pressure that they do not have a regulator on the gas meter. Knowing this I only allowed for a 1" pressure drop.
    As far as the gas valve and what gets consumed I have a document from a gas valve company. In this it states a gas valve is not a regulator. Most gas valves have a dual chamber design. You need the minimum of 5" to open the internal gate and allow gas through. If you deliver more than 10" the gate will fully express and trip shut. The gas valve will pass anything in between. (The numbers I'm using are just standard typical guides not exact.) The burner manifold will have a lower number usually 3.5 or 4" in that range. That number is what correlates with the heat exchanger's capacity for extraction coupled with either moving water or air to give us a rating of usable BTU's. Just as you can overheat a boiler or furnace (that's why we now have so many safety switches). This can happen for numerous reasons...Why give the heat exchanger more than it can efficiently use. Aim for the sweet spot. Make no mistake it will use whatever it is fed...Boilers are pigs!
  • Tim McElwain Tim McElwain @ 5:44 PM
    Contact this user

    Gas Valves

    As far as the gas valve and what gets consumed I have a document from a gas valve company. I WOULD BE INTERESTED IN SEEING THAT DOCUMENT.

     In this it states a gas valve is not a regulator. Most gas valves have a dual chamber design. SINCE 1979 GAS VALVES HAVE BEEN REQUIRED TO BE DUAL SEATED (REDUNDANT). THIS WAS DUE TO AN INCIDENT IN 1972 RELATED TO EXCESSIVE PRESSURES AND THE FAILURE OF SINGLE SEATED GAS VALVES. GAS VALVES HAVE A BUILT IN REGULATOR CALLED A SERVO PRESSURE REGULATOR. THIS REGULATOR WORKS ON DOWNSTREAM DEMAND (THE SIZE OF ORIFICES AND HOW MANY CREATE THE DEMAND) THE VALVES HAVE A DOWNSTREAM SENSING PORT ON THE OUTLET SIDE OF THE GAS VALVE WHICH SENSES THIS DEMAND AND POSITIONS THE SERVO REGULATOR TO GIVE THE EXACT PRESSURE NEEDED IN CONJUNCTION WITH THE SIZE OF THOSE ORIFICES (TYPICALLY 3.5" W.C.) VALVES CAN BE SLOW OPENING, FAST OPENING , DELAY OPENING STEP OPENING AND IN SOME CASES TWO STAGE.ALL HOWEVER HAVE A BUILT IN REGULATOR THAT CONTROLS OUTLET PRESSURE.

    You need the minimum of 5" to open the internal gate WHAT IS AN INTERNAL GATE??? GAS VALVES WILL STILL OPEN AT LESS THAN 5" PRESSURE AS THEY ARE OPENED TYPICALLY BY APPLYING POWER 24 VOLTS, 120 VOLTS OR IN SOME CASES MILLIVOLTS TO OPEN THE VALVE SEAT AND ALLOW GAS THROUGH. BY THE WAY ALL PILOTS ON HEATING VALVES ARE ON LINE PRESSURE AND ARE NOT REGULATED.

    If you deliver more than 10" the gate will fully express and trip shut. GAS VALVES WILL WORK ON PRESSURES UP TO ROUGHLY 14" W.C. SO THAT PROPANE SYSTEMS CAN OPERATE THROUGH THE SAME VALVES AS NATURAL GAS BY JUST CHANGING THE SPRING IN THE SERVO REGULATOR AND THE DOWNSTREAM ORIFICES

     The gas valve will pass anything in between. (The numbers I'm using are just standard typical guides not exact.) The burner manifold will have a lower number usually 3.5 or 4" in that range. That number is what correlates with the heat exchanger's capacity for extraction coupled with either moving water or air to give us a rating of usable BTU's. Just as you can overheat a boiler or furnace (that's why we now have so many safety switches)I ASSUME YOU MEAN OVER-GAS WHEN YOU SAY OVERHEAT. This can happen for numerous reasons...Why give the heat exchanger more than it can efficiently use. THIS IS WHY WE FIRE EQUIPMENT AT ITS MAXIMUM DESIGNED FIRING RATE AND DETERMINE THAT BY DOING A COMBUSTION ANALYSIS. Aim for the sweet spot. THE SWEET SPOT IS FINALLY DETERMINED BY A COMBUSTION ANALYSIS AND NOTHING ELSE. Make no mistake it will use whatever it is fed...Boilers are pigs!

    HOPE THAT CLEARS UP THE CORRECT OPERATION OF A GAS VALVE.

    Having said all that you still must in all cases deliver the maximum pressure available to the inlet of the gas valve, the regulator in the gas valve will determine correct firing rate along with proper orifice sizing and finally combustion testing. So if you have 7" W.C. at the outlet of the gas meter it is my stand that 40 feet away at the last appliance with all the equipment running at the same time you have as close to that 7" W.C. as you can get with a minimum if any pressure drop. sizing pipe correctly, account for lineal pipe lengths through fittings etc will take care of this. It may take a little large pipe but our job is to make sure the customer gets proper system operation at all times..
  • 4Johnpipe 4Johnpipe @ 7:36 PM
    Contact this user

    Interesting

    There are a few different types of gas valves...Lets use the propane analogy. The reason the orifice on propane equipment is smaller is because it is of a higher pressure. I would offer that even though with natural gas we are talking about very small differences in pressure the orifice will still pass slightly more when given more than required. A good example is a Mapp gas torch. It was one size orifice but can deliver different ratings of heat by adjusting the pressure going through it via the regulator.
    Combustion analysis testing is great! it allows us to connect to existing gas and adjust the pressure and or air mixture to a very exact rate. I have installed a few systems where we ran all the gas new and sized it accordingly and had little to no adjustment necessary. On the flip side I have connected to some larger existing pipe and always find myself turning the gas "down".
    Lets not forget clothes dryers, water heaters and cooking ranges...I would not think that to be safe we would run 1" or even larger just to be sure. Of course I am saying this based on my local gas company and I do not have the issues you have with yours.
    I do want to bring up one more point. If when sizing a house to deliver say 6" of water column roughly to all appliances I had a combined total of say 20 cubic feet of gas in the piping system which is after the meter and paid for by the customer. Why would I want to have larger sizes with say 30 cubic feet of gas sitting in the lines that the customer has paid for?
    I attached a copy of the drawing sent to me some time ago from Robershaw...It denotes a typical gas valve for a furnace. I was instructed that gas valves do have a regulator of sorts included in them he was clear that they are not regulators as such. The gas enters the main chamber that is activated by a call for heat. It then passes across a regulator that will open with roughly 5" WC it needs a minimum and will be forced closed if the pressure exceeded {in this case 10"WC}. The second chamber opens when a flame sensor signal is proved and allows the gas to move out of the gas valve. He was pretty clear that this is a basic working of most {not all} gas valves and yes some are able to accept 14" for LP gas.
  • Tim McElwain Tim McElwain @ 9:26 PM
    Contact this user

    Now I know why I stay in business

    There are a few different types of gas valves..BUT THEY ALL MUST COME UNDER THE SAME ANSI STANDARD.


    .Lets use the propane analogy. The reason the orifice on propane equipment is smaller is because it is of a higher pressure. IT IS ALSO BECAUSE IT HAS A DIFFERENT SPECIFIC GRAVITY AND A DIFFERENT BTU CONTENT.


     I would offer that even though with natural gas we are talking about very small differences in pressure the orifice will still pass slightly more when given more than required.  THAT WILL NOT HAPPEN IF THE REGULATOR IS SET TO THE REQUIRED GAS PRESSURE AS NOTED ON THE EQUIPMENT.


    A good example is a Mapp gas torch. It was one size orifice but can deliver different ratings of heat by adjusting the pressure going through it via the regulator. IT IS A WHOLE DIFFERENT ANIMAL THE KEY WORD IS ADJUSTING THE PRESSURE. GAS VALVES HAVE A SET OUTLET PRESSURE AND IT IS NOT ADJUSTED BUT SET TO WORK WITH THE ORIFICES IN PLACE AT THE BURNERS TO GIVE THE CORRECT INPUT.



    Combustion analysis testing is great! it allows us to connect to existing gas and adjust the pressure and or air mixture to a very exact rate. I have installed a few systems where we ran all the gas new and sized it accordingly and had little to no adjustment necessary. On the flip side I have connected to some larger existing pipe THAT SHOULD NOT MATTER AS THE VALVE WILL ONLY LET THROUGH THE AMOUNT OF GAS THE ORIFICES AND OUTLET PRESSURE WILL ALLOW. and always find myself turning the gas "down" HOW DO YOU TURN THE GAS DOWN?.
     

    Lets not forget clothes dryers, water heaters and cooking ranges...I would not think that to be safe we would run 1" or even larger just to be sure. YOU SIZE TO WHAT THE PARTICULAR APPLIANCE NEEDS FOR INPUT THE 1' PIPE WAS TO THE HEATING EQUIPMENT ONLY. I SIZE ALL OTHER PIPING AS IT IS NEEDED 1/2", 3/4" ETC 

    Of course I am saying this based on my local gas company and I do not have the issues you have with yours. I AM GLAD TO HEAR THAT YOUR GAS COMPANY NEVER HAS PRESSURE PROBLEMS. AS SOMEONE WHO WORKED FOR A GAS COMPANY FOR 28 YEARS THAT IS VERY SURPRISING TO ME.


    I do want to bring up one more point. If when sizing a house to deliver say 6" of water column roughly to all appliances I had a combined total of say 20 cubic feet of gas in the piping system which is after the meter and paid for by the customer. Why would I want to have larger sizes with say 30 cubic feet of gas sitting in the lines that the customer has paid for? TO MAKE SURE WHEN ALL THE EQUIPMENT CALLS AT THE SAME TIME SAY IN THE DEAD OF WINTER ON A SATURDAY WHEN EVERYONE IS HOME AND ALL THE EQUIPMENT IS RUNNING, COOKING STOVE FOR BREAKFAST, SHOWERS, DRYER ETC YOU NEED THAT 30 CUBIC FEET THEN.


    I attached a copy of the drawing sent to me some time ago from Robershaw...It denotes a typical gas valve for a furnace. I was instructed that gas valves do have a regulator of sorts included in them he was clear that they are not regulators as such. THEN WHAT ARE THEY?  THAT DRAWING YOU ATTACHED DOES NOT SHOW THE COMPLETE STORY. I HAVE FACTORY SPECIFIED CUTAWAYS OF ROBERTSHAW, HONEYWELL AND WHITE RODGERS THAT ARE MUCH MORE DETAILED AND ALL HAVE SERVO PRESSURE REGULATORS.

    The gas enters the main chamber that is activated by a call for heat. It then passes across a regulator that will open with roughly 5" WC it needs a minimum and will be forced closed if the pressure exceeded {in this case 10"WC}. The second chamber opens when a flame sensor signal is proved AND A MODULE SENSES PROPER MICRO-AMPS IN THE CASE YOU ARE SIGHTING THEN THE MODULE POWERS THE MAIN VALVE WHICH IS AFTER THE PILOT VALVE WHICH HAD TO BE ENERGIZED FIRST IN ORDER FOR THE PILOT TO LIGHT AS THE GAS FOR THAT PILOT ONLY FLOWS WHEN THE PILOT VALVE IS ENERGIZED THAT IS WHAT OPENS THAT FIRST VALVE NOT GAS PRESSURE. and allows the gas to move out of the gas valve. He was pretty clear that this is a basic working of most {not all} gas valves and yes some are able to accept 14" for LP gas.

    We could go on and on with this but to tell the truth you have some knowledge but you need some good gas training and I do not mean to offend with that statement it is my observation based on these postings. The reason I continue to go back and forth with you is the fact that people who know less than you and I are reading what is posted and I do not want them mis informed.
  • 4Johnpipe 4Johnpipe @ 9:49 AM
    Contact this user

    Training

    Tim no worries I do not get offended...I have a sense we are saying the same thing only different. I go to training all the time. I have CE classes regularly and participate in online education as often as I can.
    For me trying to type exactly what I am trying to say usually proves futile. I would hope one day to have a face to face with you and talk...
    I finally located the Interpretive Response from Gastite attached here... 
    Cheers...
  • 4Johnpipe 4Johnpipe @ 9:58 AM
    Contact this user

    Update

    PS I was contacted back yesterday from Gastite. They no longer publish updated letters like this as now the entire D&I guide is approved by the standards listed in the manual.
  • icesailor icesailor @ 10:26 AM
    Contact this user

    Massachusetts?

    Does that include approval of and by the board of Plumbers' and Gasfitters' in Massachusetts? Just because it says that is listed by the printed standards, may not mean the that interpretation is OK. There might be a superceeding interpretation by the Board which makes the Gastite "suggestion", moot. I don't remember in my last Massachusetts CE class, anything about sizing gas pipe that small except for LPG. In Massachusetts, inspectors get twice the extra training we do. The Board has pretty much trained that "I like to see it like this, in spite of what the code says" attitude out of inspectors now. Everyone is mostly on the same page. Its usually not worth arguing with inspectors. If you don't agree with one, you can call the board and get an instant ruling. For or against. I've not seen problems with gas flow in oversized gas lines. But I sure have on undersized installations. Why take the chance? So you can sell more undersized jobs and have problems?
    Some would pipe a whole job with 3/8" OD ACR tube if someone else told them it was legal. Just to try to get the job cheaper.
  • 4Johnpipe 4Johnpipe @ 1:26 PM
    Contact this user

    Massachusetts

    Please don't get me wrong it is not about under sizing jobs. The fact of the matter is most jobs are just plain oversized. If your state has adopted the IFGC code I would recommend for a few extra dollars buying the IFGC Commentary edition of the code book. The authors of the code went to great lengths to publish this edition so inspectors would not have to interpret for themselves the intent of the code. My gas company New Jersey Natural Gas  has gone so far to say they wished more would size accordingly so they would have less cost in the distribution side of delivering gas. That is a direct quote from them.
    Further on in the opening paragraphs under "Purpose" of the IFGC it states "The intent is to minimize the hazards associated with the use and distribution of highly flammable  / explosive fuel gasses". I see the best way in accomplishing this is to take a little more time to do the math and size systems using the most accurate means available as in the "Summation Method". That said I have had my fare share of discussions with inspectors that were not at all familiar with it and have a packet ready for submittal to some towns that may request it. It does help now that I am also a licensed inspector to have these discussions however I started using this method before I obtained my credentials.
    Being the skeptic I am by nature I have an several occasions gone back and tested my gas systems with a digital manometer under forced full fire conditions and have never delivered inadequate pressure anywhere. I was pleasantly surprised to see within 10ths readings that correlated with the math presented with my riser diagrams. This goes back to roughly 2003.
  • 4Johnpipe 4Johnpipe @ 2:41 PM
    Contact this user

    Tables

    Yes Rob it is not possible to run 1/2" CSST for a Navien. I pulled up the spec page on Navien it is similar to Rinnai which is what I install. I would not recommend running piping smaller than the inlet of the appliance period. I don't care what the manufacturer reps say. You will undoubtedly  at the least have a velocity or noise issue. Not to mention what ever the line is connected to would suffer. A standard law of physics is high pressure goes to low pressure. These negative pressure combustion chambers drop pressures far below atmospheric and this will gas a much easier path for the flow of gas which may in turn starve something else of its minimum required pressure.
    Rinnai issued a technical update a few years ago to increase any CSST to 1" to avoid system harmonics. I have seen this myself it sounds just like blowing into an open bottle of your favorite beverage...
  • 4Johnpipe 4Johnpipe @ 2:43 PM
    Contact this user

    Tables

    TablesYes Rob it is not possible to run 1/2" CSST for a Navien. I pulled up the spec page on Navien it is similar to Rinnai which is what I install. I would not recommend running piping smaller than the inlet of the appliance period. I don't care what the manufacturer reps say. You will undoubtedly  at the least have a velocity or noise issue. Not to mention what ever the line is connected to would suffer. A standard law of physics is high pressure goes to low pressure. These negative pressure combustion chambers drop pressures far below atmospheric and this will cause a much easier path for the flow of gas which may in turn starve something else of its minimum required pressure.
    Rinnai issued a technical update a few years ago to increase any CSST to 1" to avoid system harmonics. I have seen this myself it sounds just like blowing into an open bottle of your favorite beverage...
    This post was edited by an admin on March 29, 2014 2:46 PM.
  • Bob Harper Bob Harper @ 7:13 AM
    Contact this user

    no relief from codes

    While a mfr. may claim their equipment is resistant to low inlet pressure regimes, that does not relieve the installer of the responsibility to pipe the appliance in accordance with the codes including the sizing charts. This valve may be a little resistant to sudden burps or dips but the bottom line is, you have to supply sufficient gas to the appliance to fire at its rating-period. 
  • RobG RobG @ 12:48 PM
    Contact this user

    4johnpipe

    I might be misunderstanding you. First you stated that 1/2" pipe would be be adequate for 199,000 BTU's using the "summation method".  Then you stated that I was was correct, you looked at the tables for Navian and realized that no, 1/2 would not cut it but that you misspoke because you use Rinnai. Are the sizing methods different between the two brands? Then you said that you would never install a gas line smaller than the inlet of the appliance. Please show me a Rinnai water heater or boiler with a gas inlet smaller than 3/4". I'm at a loss.

    Rob
  • 4Johnpipe 4Johnpipe @ 8:08 PM
    Contact this user

    At A Loss

    Rob I thought you were quoting something a manufacturer rep told or instructed you about the Navien. My bad I assumed Navien to have a 1/2" gas inlet. Rinnai does not. The equation I posed earlier was based on an available 7.5" of water column at the connection to the gas. An example would be a run directly from the gas meter.
    Example: If we have 7.5" WC at the meter and the appliance requires 5" the 1/2" iron pipe has a .067" WC pressure drop per foot at 200K BTU's ~~ .067" WC x 24' of pipe = 1.608" WC pressure drop in that section. Take the starting point in this case of 7.5" WC subtract the 1.608" WC = 5.892" WC delivered to the appliance. That said I am full aware of velocity issues with negative pressure combustion chambers and would not install smaller than the opening of the gas valve.
    PS quite a few boilers (at least natural draft) I install for residential have a 1/2" gas connection.
    This post was edited by an admin on March 30, 2014 8:11 PM.
  • 4Johnpipe 4Johnpipe @ 8:39 PM
    Contact this user

    Job Example

    Take a look at this job. This was submitted with the permits. The 2" was existing but ended up needing to be changed anyway. The worksheet shows pipe type, BTU's, section pressure drop and delivered pressure. This may clear it up. This was all rigid pipe.
  • heatpro02920 heatpro02920 @ 5:29 PM
    Contact this user

    I can tell you first hand

    that you can not run a Rinnai tankless on 1/2 gas line...

    I have gone to units that other people have installed because they cant get them to run rite and the bulk of them were insufficient volume... I seen one that was in service for 2 years, and once in a while they would get cold hot cold hot cold hot {but no error faults}, they wanted me to install a second one because the original installer told them their shower used too much water for a single unit.... I changed the gas line and it fixed the issue instantly....

    Anyway, when it comes to gas lines, run them big to be safe... For a single tankless short run I may run 1" but normally run 1 1/4", the cost isn't much difference... Do it rite do it once...
  • Ironman Ironman @ 10:19 PM
    Contact this user

    Tim

    Any word back from Navien?

    We know they monitor this site. Why don't they reply?
    Bob Boan



    You can choose to do what you want, but you cannot choose the consequences.
  • Tim McElwain Tim McElwain @ 12:10 PM
    Contact this user

    No I have nopt heard from them

    as of today. I will be busy with classes starting tomorrow so will not be able to pursue this.

    As for why gas valves and other hookups to appliances are a certain size say 1/2" or 3/4 " it has to do with several things one of which is related to ANSI Standards testing. All gas valves have charts giving you the allowable pressure loss through the gas valve at various sizes ex a gas valve 1/2" x 1/2" has a different loss than a valve 3/4"m x 3/4". Most of us in the gas industry allow for a 1" pressure drop through the gas valve when sizing. That is in most cases much more than is needed in fact a Honeywell VR 8300 A 3/4" x 3/4"  24 volt, standing pilot valve does not reach a 1" drop until it is fired at 200,00 BTU's or more and then the drop increases as you go up in BTU. So the 1/2" x 1/2" size assumes (manufacturer assumes) the installer will know enough to supply adequate pipe size to that 1/2" valve to make sure the burner fires at full input all the time.

    Think about this most meter bars are 3/4" so does that mean we run 3/4" pipe to all the appliances. I hope not and in fact you may see that increased right at the point of delivery to 1 1/4" or 1 1/2" pipe.
  •  
Post a Reply to this Thread