# furnace blowing out water heater pilot



## studmaster1 (Dec 10, 2011)

Have an issue at work where our HVAC dept. installed a fan assisted furnace into a masonary (unlined) chimney. Customer says pilot to heater (nat. draft) has been going out ever since furnace was installed. Water heater is 5 years old and I found no problems with it. Chimney is on exterior wall and my thinking was the cold air in chimney is not allowing the furnace draft propery (esp. when furnace kicks on initally in the pre-purge phase) and ends up blowing out pilot. HVAC manager says I don't know what I'm talkng about (maybe true). Anybody have any thoughts on this or am I (like everyone says) an idiot?


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## OldSchool (Jan 30, 2010)

studmaster1 said:


> Have an issue at work where our HVAC dept. installed a fan assisted furnace into a masonary (unlined) chimney. Customer says pilot to heater (nat. draft) has been going out ever since furnace was installed. Water heater is 5 years old and I found no problems with it. Chimney is on exterior wall and my thinking was the cold air in chimney is not allowing the furnace draft propery (esp. when furnace kicks on initally in the pre-purge phase) and ends up blowing out pilot. HVAC manager says I don't know what I'm talkng about (maybe true). Anybody have any thoughts on this or am I (like everyone says) an idiot?


Just reread your post and its the hwt thats going out LOL .... to early this morning


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## Tommy plumber (Feb 19, 2010)

Chimneys are supposed to be lined. But I was thinking, where do the vents enter into the chimney? The smaller BTU appliance's vent is supposed to be higher up on the chimney with the larger BTU appliance entering below the other vent connector.


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## OldSchool (Jan 30, 2010)

Its code here to install a liner for all masonary chimneys....

more than likely it is not drafting up the chminey because the chimney is to cold..

Check the draft at the draft hood of the hwt


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## BROOKLYN\PLUMB (May 21, 2010)

Your not supposed to put a natural draft and induced draft on the same chimney.


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## jnohs (Jan 27, 2012)

BROOKLYN\PLUMB said:


> Your not supposed to put a natural draft and induced draft on the same chimney.


i agree


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## SimplePlumber (Feb 1, 2012)

I would speculate that either the new furnace has a bigger draw on a possibly undersized gas line..which will suck out the w/h pilot light under load, or as most have stated, the power venting sucking too much draft past the w/h pilot to stay lit.

Be well,

Rich


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## BROOKLYN\PLUMB (May 21, 2010)

Check for flu spillage from water heater when boiler purges and cycles, also how are they tying in to the chimney (y, next to each other, small over large)


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## Cotton06 (Jul 9, 2011)

Check the draft on the water heater while the furnace is on, it could be down drafting putting the pilot out.


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## ZL700 (Dec 8, 2009)

BROOKLYN\PLUMB said:


> Your not supposed to put a natural draft and induced draft on the same chimney.


Thats not true, besides look at all the venting tables that include charts for Nat + Nat, Nat + Fan, Fan + Fan, .........

Draft induced always requires properly sized and lined chimney.

Furnace induced draft exhaust fan blows out pilot on the tank? for sure spillage of furnace taking place here, dangerous condition for CO there!


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## BROOKLYN\PLUMB (May 21, 2010)

ZL700 said:


> Thats not true, besides look at all the venting tables that include charts for Nat + Nat, Nat + Fan, Fan + Fan, .........
> 
> Draft induced always requires properly sized and lined chimney.
> 
> Furnace induced draft exhaust fan blows out pilot on the tank? for sure spillage of furnace taking place here, dangerous condition for CO there!


I don't know the charts that you speak of but we're not allowed (I will try to find code, ofcourse there are also a million memorandum) and if you have two forced vents I believe the chimney must be induced and interlocked 
Any MP's from NYC please correct me if I am mistaken


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## BROOKLYN\PLUMB (May 21, 2010)

*503.3.3 Mechanical draft systems. *

Mechanical draft systems shall comply with the following: 
1. Mechanical draft systems shall be listed and shall be installed in accordance with the manufacturer’s installation instructions for both the appliance and the mechanical draft system. 

2. Appliances, except incinerators, requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design. 

3. Forced draft systems and all portions of induced draft systems under positive pressure during operation shall be designed and installed so as to prevent leakage of flue or vent gases into a building.

4. Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operating under positive pressure. 

5. Where a mechanical draft system is employed, provisions shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance. 

6. The exit terminals of mechanical draft systems shall be not less than 7 feet (2134 mm) above grade where located adjacent to public walkways and shall be located as specified in Section 503.8, Items 1 and 2.


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## ZL700 (Dec 8, 2009)

IN NYC you use something other than NFPA 54 / ANZI Z223?
International code trump residential too?
These are the venting standards referenced in every manufacturers installation manual. 
Canada is different using B149


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## BROOKLYN\PLUMB (May 21, 2010)

I copied it from the ICC pretty much the same as ours just couldn't copy


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## BROOKLYN\PLUMB (May 21, 2010)

NYCFGC NYCFuel Gas Code


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## OldSchool (Jan 30, 2010)

http://www.creia.org/January-2011-Inspector-eNews/common-venting-of-gas-appliances.html

Go to the above link and it explains everything


Category I Furnaces are the type most commonly used for residential heating. They include old-fashioned gravity vent furnaces and the newer fan-assisted Plus 80 models, also known as induced draft furnaces. In a gravity vented furnace, the heat of combustion provides sufficient stack effect to enable safe venting of combustion byproducts. Stack effect occurs because the hot gases inside the flue have lower density that the cooler atmosphere outside the flue. 

A Plus 80 furnace is designed for greater fuel efficiency than a standard gravity vented furnace. This is achieved by lengthening the heat exchanger to allow more heat transfer into the circulating air. But longer heat exchangers produce draft resistance and they lower the temperature of the exhaust gases relative to atmospheric temperature. To enable proper venting, an inducer fan is built into the system. The fan applies a slight negative pressure on the heat exchanger to ensure that the products of combustion are evacuated upward. The fan, however, does not exert positive pressure into the flue pipe. The exhaust in the flue is gravity-vented. Therefore, its vent pressure is rated as “non-positive,” which is why it can be vented in common with a gravity vented water heater.


Sent from my portable office....yes I am at work


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## Don The Plumber (Feb 14, 2010)

Problem is most likely 1 of 2 things.

#1-Clogged or partially clogged chimney.
or
#2- Not enough makeup air, in furnace/ water heater room.

Also,Nat draft & Fan assist are on same chimney all the time, around here, & perfectly legal. Have that exact set up in my own house.


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## RW Plumbing (Aug 16, 2010)

Don The Plumber said:


> Problem is most likely 1 of 2 things.
> 
> #1-Clogged or partially clogged chimney.
> or
> ...


+1 on item #2


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## Plumber71 (Dec 20, 2010)

What size chimney is there ? Maybe it is to small .


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## HOMER (Jun 5, 2011)

a defective gas meter can create pilot outage

could also be a defective water heater .
is that 5 year old water heater a sealed firebox type that needs the air inlet screen cleaned ?


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## Plumber Jim (Jun 19, 2008)

Put a manometer on the gas valve of the water heater and fire both the furnace and water heater and see what reading you get.


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## Don The Plumber (Feb 14, 2010)

Plumber Jim said:


> Put a manometer on the gas valve of the water heater and fire both the furnace and water heater and see what reading you get.


 
Perfect advice. I like this idea, of what could be the problem, better than my own suggestion:yes:. I had a bad gas meter one time, & each appliance would work great, while I was there, but then pilot would go out on heater, after I left.

I had actually replaced the water heater, which was old anyway, so I didn't feel guilty about replacing it. When I fired up the new heater, all was well, until the furnace came on.Put Manometer on manifold to heater,& 4" w.c., went down to nothing, with furnace on. Bad gas meter.

Now this is one of the 1st things I check, on pilot outages.


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## MikeS (Oct 3, 2011)

Don The Plumber said:


> Perfect advice. I like this idea, of what could be the problem, better than my own suggestion:yes:. I had a bad gas meter one time, & each appliance would work great, while I was there, but then pilot would go out on heater, after I left.
> 
> I had actually replaced the water heater, which was old anyway, so I didn't feel guilty about replacing it. When I fired up the new heater, all was well, until the furnace came on.Put Manometer on manifold to heater,& 4" w.c., went down to nothing, with furnace on. Bad gas meter.
> 
> Now this is one of the 1st things I check, on pilot outages.


so I am clear on this, when the furnace kicked on, it pulled so much gas from the water heater, it snuffed out the pilot?


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## studmaster1 (Dec 10, 2011)

BROOKLYN\PLUMB said:


> Check for flu spillage from water heater when boiler purges and cycles, also how are they tying in to the chimney (y, next to each other, small over large)


It's small (water heater) above furnace.


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## studmaster1 (Dec 10, 2011)

Plumber71 said:


> What size chimney is there ? Maybe it is to small .


,chimney is adequate size, the gas supply in and out of gas control valve is normal. Problem is noticed most often in the morning.


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## studmaster1 (Dec 10, 2011)

HOMER said:


> a defective gas meter can create pilot outage
> 
> could also be a defective water heater .
> is that 5 year old water heater a sealed firebox type that needs the air inlet screen cleaned ?


Yes, and screen and burner assem. Cleaned.


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## MikeS (Oct 3, 2011)

ok, so this is a new water heater, and a new furnace, both vents tied into a chimney? Is this correct?
And the water heater still has pilot outtages?


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## studmaster1 (Dec 10, 2011)

Plumber Jim said:


> Put a manometer on the gas valve of the water heater and fire both the furnace and water heater and see what reading you get.


Good idea but problem is intermittent, and gas pressure was fine.


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## BROOKLYN\PLUMB (May 21, 2010)

Perhaps it's a coincidence and the thermocouple is going on water heater


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## MikeS (Oct 3, 2011)

If you suspect the furnace has something to do with this, it should be real easy to test. Just turn on the furnace, and watch the pilot. At the same time, it should be easy to see if your water heater is spilling. Turn up the thermostat on the water heater, and, feel the vent pipe. Or, use a match to see if it is drawing. More than likely, if this is a 5 year old water heater, its time for a new thermocouple. Or, clean out the pilot. Not much causes a water heater to shut down. If the thermocouple gets cold, it will shut down. Why does it get cold? Because it doesn't have a flame on it. why doesn't it have a flame on it? thats for you to figure out.


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## studmaster1 (Dec 10, 2011)

MikeS said:


> ok, so this is a new water heater, and a new furnace, both vents tied into a chimney? Is this correct?
> And the water heater still has pilot outtages?


Correct, it may well be a coincidence that the thermocouple has gone bad right when the furnace was installed. The heater is fairly new (4 years) and yes both vents are tied into the same chimney, but the chimney is an exterior (3 sides exposed to ouside) and it isn't lined. I climbed on the roof and looked down it and saw some cracks in the tile so a down draft is also possible. My thinking was being on the ext., with the cold weather the morning, the furnace kicks on and the exhaust, at first, has trouble drafting up the chimney and ends up blowing out the pilot. The 40 gal. Water heater also only has a 3" connector, though it connects to the chimney within 3', the furnace connector is 4" b vent and is about 6' from the chimney connection. I'm really just irritated because the chimney is unlined and the hvac dept. Never pulled a permit. I have a commission only job and the office won't pay me because they believe the hvac manager over me. Thanks to everyone for your help, I appreciate all your advice but in this case I think I'm gonna have to eat a doo-doo sandwich, after all ,like my dad taught me, "don't get in a pi$$ing contest with a d1(k.".


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