gas water heater help - Plumbing Zone

express · 07-03-2009, 04:52 PM

I installed a natural gas water heater the other day and immediately felt hot air coming from under the bonnet which would indicate a blocked flue. had customer set up for a chimney sweep to check out flue. Says it is not blocked but because the furnace does not use the flue any more it is over sized for the hot water heater, advise is to reline making it smaller. I'm not sure if I'm buying this, I would think if it was over sized it would take a little longer to heat up the air in the flue to get it moving. Would like any feed back on this. ( not stating weather pex or copper was used for this installation)
thanks Steve

uaplumber · 07-03-2009, 09:13 PM

LINER!!

You are allowing exhaust gasses into the home.
A chimney that is too large will not allow for a proper "stack effect"
The gasses will go up until they cool then they will come back down.

What size chimney is it, what is the length, how long is the lateral from the HWT to the chimney?

breid1903 · 07-03-2009, 09:14 PM

it sounds like we have negative pressure in the house. i have seen where the furnace or ac fan will draw done the chimney. sometimes it's combustion air circulating around each other in a circle. usually goes up furnace flue to tee then back down and out the wh. not the problem here. i hope not. if we have furnace cold air return and wh near to each other, not separated by doors. so when fan runs we have a high & low sides. output side is high and return side is low. that's the inside of house, outside is between them. high pressure goes to low pressure, always. if high is +6psi and outside is 0psi, well we have air escaping. that's not important here. but if low side is -6psi, air comes in because of high to low. turn off ac and stop all air flow in house. that will answer that. ac fans are normally higher speed than heating speed.............chimney will no draw correctly the air just circulates in it. look in your gas code book there are tables of diameters and lengths for vents. if it's not lined we have a carbon monoxide problem and a acid rotting chimney. liner will work better if it insulated if it gets cold out in winter. breid

leak1 · 07-03-2009, 09:34 PM

liner!

Plumber Jim · 07-04-2009, 12:55 AM

I agree, you shouldn't have the water heater venting into an unlined chimney. If you have issues with negative pressure like running a atic fan with not enough windows open that should also be addressed.

express · 07-04-2009, 06:49 AM

Ok guys its running into the same chimney it always has so I guess they do need a liner. thanks again for the help.

SewerRatz · 07-04-2009, 09:02 AM

Thing that baffles me about this is the water heater vented into this chimney along with the furnace. But the furnace only runs , lets say 6 months out of the year. So does this mean they had this issue the 6 months the furnace did not run? I mean with out the furnace running in the summer months wouldn't the chimney be considered over sized during that time as well?

express · 07-04-2009, 12:57 PM

good point Ron, so what do you guys have to say about that.

Plumber Jim · 07-04-2009, 01:24 PM

Do you know for a fact that the old water heater didn't have exhaust gases backing out the hood? Maybe your just the first person to pay close enough attention and notice it. Here we have to have the chimney lined no choice. also is there any other things going on that the customer may have not told you? attic fan on or something you missed?

breid1903 · 07-04-2009, 04:14 PM

there is a good chance, real good that it did this 365 days a year. when furnace wasn't cooking even in winter. i have seen houses with large chimneys that showed no vapor in the winter. i run every morning and it became a game to watch. i presumed that the chimney was circulating inside itself. some also leaked so bad that they didn't show a draw. ..............when i said insulated, i meant double wall..................all chimneys around here were built for solid fuel (wood or coal). breid

07-03-2009, 04:52 PM	#1
express Senior Member Join Date: Nov 2008 Posts: 136 My Photos	gas water heater help I installed a natural gas water heater the other day and immediately felt hot air coming from under the bonnet which would indicate a blocked flue. had customer set up for a chimney sweep to check out flue. Says it is not blocked but because the furnace does not use the flue any more it is over sized for the hot water heater, advise is to reline making it smaller. I'm not sure if I'm buying this, I would think if it was over sized it would take a little longer to heat up the air in the flue to get it moving. Would like any feed back on this. ( not stating weather pex or copper was used for this installation) thanks Steve

07-03-2009, 09:13 PM	#2
uaplumber Plumbing Contractor Join Date: Jun 2008 Location: Westlock, Alberta, Canada Posts: 1,417 My Photos	LINER!! You are allowing exhaust gasses into the home. A chimney that is too large will not allow for a proper "stack effect" The gasses will go up until they cool then they will come back down. What size chimney is it, what is the length, how long is the lateral from the HWT to the chimney? __________________ B&B Plumbing Inc http://www.westlockplumber.com Plumbing and Heating in Westlock, Alberta

07-03-2009, 09:14 PM	#3
breid1903 Senior Member Join Date: Feb 2009 Location: fulton, indiana Posts: 166 My Photos	the chimnay should be relined. it sounds like we have negative pressure in the house. i have seen where the furnace or ac fan will draw done the chimney. sometimes it's combustion air circulating around each other in a circle. usually goes up furnace flue to tee then back down and out the wh. not the problem here. i hope not. if we have furnace cold air return and wh near to each other, not separated by doors. so when fan runs we have a high & low sides. output side is high and return side is low. that's the inside of house, outside is between them. high pressure goes to low pressure, always. if high is +6psi and outside is 0psi, well we have air escaping. that's not important here. but if low side is -6psi, air comes in because of high to low. turn off ac and stop all air flow in house. that will answer that. ac fans are normally higher speed than heating speed.............chimney will no draw correctly the air just circulates in it. look in your gas code book there are tables of diameters and lengths for vents. if it's not lined we have a carbon monoxide problem and a acid rotting chimney. liner will work better if it insulated if it gets cold out in winter. breid

07-04-2009, 12:55 AM	#5
Plumber Jim Senior Member Join Date: Jun 2008 Location: Colorado Posts: 1,113 My Photos	I agree, you shouldn't have the water heater venting into an unlined chimney. If you have issues with negative pressure like running a atic fan with not enough windows open that should also be addressed. __________________ Broomfield Plumber , Denver Plumber , Boulder Plumber , Lafayette Plumber

07-04-2009, 09:02 AM	#7
SewerRatz Illinois Licensed Plumber Join Date: Apr 2009 Location: Chicago Area Posts: 1,338 My Photos	Thing that baffles me about this is the water heater vented into this chimney along with the furnace. But the furnace only runs , lets say 6 months out of the year. So does this mean they had this issue the 6 months the furnace did not run? I mean with out the furnace running in the summer months wouldn't the chimney be considered over sized during that time as well? __________________ Ron Hasil Lic #058-160417 A-Archer Sewer & Plumbing specializing in: Tankless Water Heaters \| Drain and Sewer Cleaning Sump and Ejector Pumps \| Backflow RPZ Testing

07-03-2009, 09:34 PM	#4
leak1 master of disaster Join Date: Mar 2009 Location: ohio- usa Posts: 716 My Photos	liner!

07-04-2009, 06:49 AM	#6
express Senior Member Join Date: Nov 2008 Posts: 136 My Photos	Ok guys its running into the same chimney it always has so I guess they do need a liner. thanks again for the help.

07-04-2009, 12:57 PM	#8
express Senior Member Join Date: Nov 2008 Posts: 136 My Photos	good point Ron, so what do you guys have to say about that.

07-04-2009, 01:24 PM	#9
Plumber Jim Senior Member Join Date: Jun 2008 Location: Colorado Posts: 1,113 My Photos	Do you know for a fact that the old water heater didn't have exhaust gases backing out the hood? Maybe your just the first person to pay close enough attention and notice it. Here we have to have the chimney lined no choice. also is there any other things going on that the customer may have not told you? attic fan on or something you missed? __________________ Broomfield Plumber , Denver Plumber , Boulder Plumber , Lafayette Plumber

07-04-2009, 04:14 PM	#10
breid1903 Senior Member Join Date: Feb 2009 Location: fulton, indiana Posts: 166 My Photos	chimney there is a good chance, real good that it did this 365 days a year. when furnace wasn't cooking even in winter. i have seen houses with large chimneys that showed no vapor in the winter. i run every morning and it became a game to watch. i presumed that the chimney was circulating inside itself. some also leaked so bad that they didn't show a draw. ..............when i said insulated, i meant double wall..................all chimneys around here were built for solid fuel (wood or coal). breid

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