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Tim McElwain

Tim McElwain

Joined on August 17, 2009

Last Post on April 21, 2014

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Let me look at what you posted

@ March 27, 2014 6:51 PM in Gas piping

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.

Sorry nothing from Navien

@ March 26, 2014 7:08 PM in Gas piping

I also called and left a message so maybe tomorrow.

Both the state and the

@ March 26, 2014 4:49 PM in Gas piping

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).

Fan-in-a-Can is matched

@ March 25, 2014 7:16 PM in adding Walls around Boiler

to the total BTU's in the space not the size of the space. You do however have to deal with fire codes on keeping the equipment cool based on size of the room.

Make sure they are going to tie in with interlocks all the equipment. What that means is the fan has to be running or the equipment will not operate, it is a vital safety requirement.

My Gastite Manual is at my training center

@ March 24, 2014 9:44 PM in Gas piping

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.

4 john pipe are you an

@ March 24, 2014 9:12 PM in Gas piping

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

Send me the names of the

@ March 24, 2014 8:25 PM in adding Walls around Boiler

plumbers who put in the boilers by e-mail. My e-mail is gastc@cox.net I am in RI and I have a Gas Training Center and know a lot of the Mass plumbers so maybe we can get you some help.

You still need air for combustion

@ March 24, 2014 8:07 PM in adding Walls around Boiler

in the basement. If you are not going to add the walls then eliminate a window as a window and have it used with ducts to supply the needed air. Are there any other appliances such as a dryer in the space or dryers assuming this is a two family dwelling with two boilers and two water heaters.

This can be easily solved, again I would suggest getting a pro to come and take a look at what needs to be done and get a price.

What area of the country are you in?

The entire 30 x 35 x 7 can

@ March 24, 2014 7:50 PM in adding Walls around Boiler

only handle 147.000 BTU's. You have 286,000 in an even smaller room. It is a confined space all the way so you are going to have to bring air from outdoors or use a fan -in- the- can from Field Controls. The louvered door will not be sufficient for air for combustion and besides it is against fire code to be used on a boiler room unless it is equipped with fusible links that melt in a fire and close the louvers.


The Fan- in- a- can must also be interlocked with all the appliances in the space. I would suggest you get a professional to do this. The fact that people will be working out in this area means all protection against killing yourselves must be taken. Carbon Monoxide is caused by lack of air for combustion so as you can see someone could DIE if you do not follow the rules. I realize you are a novice so I am being very nice and saving yours or someone else's life.

Do you know how to

@ March 24, 2014 10:33 AM in weil mclain gv gold lockout problems

check with a digital manometer across the pressure switch? It sounds like the pressure switch is not pulling in. I am on my way out but check that and I will get back to you later today.

What is the

@ March 23, 2014 7:11 PM in adding Walls around Boiler

BTU input to each of the appliances? What size will the room be when completed? It is assumed by your posting that this will be a confined space. As already stated it will require 50 cubic feet per 1,000 BTU's of the total input installed in the room.

If you are going to get air for combustion from inside the building you must have two openings one 12" from the ceiling and one 12" from the floor. The size of the openings as a minimum free area of not less than 1 square inch per 1,000 BTU's but not less than 100 square inches (10" by 10"). If communicating with other spaces the volume of that space can be considered.


Method 1 all air from outdoors using vertical ducts it is 1 square inch per 4,000 BTU's. If using horizontal ducts it is 1 square inch per 2,000. Same rules for locations.


There is also a Method 2 rule allowing 1 opening; it must be 1 square inch per 3,000 BTU's and be not less than the sum of the areas (in square inches) of all the vent connectors on the appliances.


I would also have a combustion analysis done on all the equipment, install Carbon Monoxide detectors (at least three) low level that alarm at 9 PPM.


Will there be a clothes dryer in that same room or a washing machine?

Is the radiant zone

@ March 22, 2014 6:43 PM in Relay Wiring

on one of the Taco Zone Valves? Typically the zone valves are powered by the sensing control and the end switch on the zone valve brings on the relay which fires the burner and brings on the circulator. I am not completely aware of what the i -link SP-81 does?

Will do Bob,

@ March 22, 2014 6:37 PM in Gas piping

I am still waiting they will probably get back to me on Monday, I hope. If not I will call them.

There are remediation companies

@ March 21, 2014 6:14 PM in are asbestos risks overblown?

that will come in on steam boilers and do a fiberglass wrap which is acceptable for repair to asbestos that has come loose. They would be able to tell you if yours is past repair and then give you a price to have them remove it completely. YES IT IS DANGEROPUS AND NEEDS PROS TO HANDLE IT.

They acknowledged my inquiry

@ March 21, 2014 6:04 PM in Gas piping

but stated they were taking my question under advisement.

Negative pressure gas valves do not suck in

@ March 21, 2014 11:57 AM in Gas piping

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.

Rob I just sent of an inquiry to

@ March 20, 2014 5:41 PM in Gas piping

the folks at Navien lets see what they have to say.

Funny you should ask

@ March 20, 2014 5:25 PM in Gas piping

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.

Well, well the

@ March 20, 2014 11:22 AM in Original Equipment

old Honeywell V8031A I remember them well!

Send some pictures

@ March 20, 2014 11:19 AM in Dave

of controls I may be able to help you.

Is the burner coming

@ March 19, 2014 5:51 PM in HOME OWNER

on when the thermostat calls for heat? Does the hot surface igniter glow? Your furnace has an Electronic Fan Timer which delays bringing the blower on for either 30 or 60 seconds. For that to happen the combustion air blower must come on the pressure switch has to close and then the igniter glows and hopefully ignites the main burner. The next thing to happen is for the system fan to come on either 30 or 60 seconds later. Check this sequence and see what is not happening.

Yes the

@ March 19, 2014 5:09 PM in gas valve on slant fin

boiler should be set up in accordance with Slant Fin instructions. They can be found at www.slantfin.ca/documents/441.pdf

How is you system vented?
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