water heater flue spillage

Steamhead (in transit)

is somehow pulling air out of the space. That's sucking flue gas from the chimney. Find the opening and close it.

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Heatman_2

water heater not venting correctly

STUMPED!! Have customer who has carbon monoxide detector next to newer 80% lennox furnace and AO Smith newer water heater. Flue downdrafts when furnace blower motor runs, sets off CO alarm. Kill blower motor, flue has proper draw. Checked cap and pipe, simple 5" b-vent ran straight through story and half. I even disconnected all venting (breaching), same scenerio, draw with a/c off, backdraft with on. Please help.

Heatman_2

The door to this mechanical/ laundry room stays open all the time. Both appliances are 4 years old and this just started happening about 2 weeks ago. I have had this problem before with attic fans and plugged soffit vents causing a negative draw on the b-vent, but this house has no attic fan. When I shut-off the a/c, the b'vent has positive draw. I'm with you, but where could my problem be?

Steamhead (in transit)

Something changed

and you need to find out what it is. This is a dangerous situation, and I'm glad you know that ;-)

The first thing I'd check is the return ducting- maybe there's a register that was recently opened. Same with a supply register that was recently closed.

Or maybe the filter is so badly plugged that the air is being sucked in thru cracks in the air handler casing.....

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Heatman_2

Filter is clean, simple $2.00 pleated. Very clean people, all registers open and clear. I will return tomorrow, what would you check next? I'm stumped. Simple 1,200 sq. ft. split level, 30 years old.

Steamhead (in transit)

Looks like

you've checked all the obvious things.... maybe light a candle or something and use the smoke to trace the air flow.....

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Heatman_2

good idea, thanks!

Jim Davis_3

Has to be a loose connection or end cap on the return duct. Quick fix until you find the leak is to cut a supply register on the plenum and adjust it with a draft guage in the water heater flue.

Nron_19

back draft

check the air intakes into the building make sure you have the proper combustion air for your appliances ,
the fan on ac is usually on high speed and heating on the next speed down

Mitch_4

sounds like

it is one of 2 possibilities.

The blower is drawing too much air fromthe space causing a downdraft situation, or;

there may also be a hole in the Heat Exchanger.

If this is a new situation, there has been no change in the structure, air supply, ducting, etc..start looking for a hole.

Glen

yes - what has changed????

but I would be looking at the return ducting of the AC equipment - or a blower door is off pulling air from the space. This is not uncommon problem -

Rich L.

Same problem

I had the same problem a couple of years ago in an old house in Cedar Rapids. Water heater vented fine when running by itself, as soon as the furnace started it backdrafted back down the water heater flue.

I took the flue apart where it entered the brick chimney and found about two foot high of bird nesting materials, as well as a bird or two. It appeared that when the water heater was running there was enough room through the nesting materials for it to draft but as soon as the draft booster on the furnace kicked on it couldn't handle the extra volume of flue gasses. The "extra" came back through the DWH flue. After cleaning it out with a coat hanger and a five gallon bucket, it went back to venting fine. I strongly recommended a new chimney cap to the owner as well.

You said you had the flue disassembled. Could you see up through it? If it offsets you may need to go on the roof and look down as well.

Good luck, Rich L.

mark o

flue

are you able to read draft electronicly that you can record numbers , draw a diagram and check blower statis pressures ( total esp) Thats a good start