Doug-

Great advice -- and you're right, I think those (2) furnaces are indeed
sucking a huge amount of combustion air out of the house -- and I plan
to replace them with a high-efficiency (90+ AFUE) unit in the spring.
I'm leaning towards Trane or Rheem -- but Bryant is in the top (3),
too...

Here's what I did last night that seemed to help: checked the ductwork
in the basement for any blocked or closed vents/returns. There is a
single large return that is unblocked -- but there were (2) vents (one
in the "newer" ductwork run in the 70s, I think) and (1) buried in the
cement-finish ceiling where I can't actually see the duct, just the
vent.

They were both closed.

I opened them both, figuring that it would improve and negative air
pressure situation in the basement (2 vents closed, 1 large return =
sucking more air away from water heater).

This seemed to help. The top of the water heater cooled off, and the
flue pipe got hot. So far, so good.

The new furnace will be vented out the side of the house (probably
right through the chimney; neighbor has it that way) -- but the water
heater actually has it's very own, dedicated chimney and flue --
totally on a different side of the house, so I'm hoping it can stay
that way.

I'll post again if I find out more...


Thanks!


Doug Boulter wrote:
wrote on 21 Jan 2007:

It is actually (2) Bryant furnaces
"daisy-chained" together (because at the time, they told the
owner that "we don't make a furnace powerful enough to heat your
home -- you'll need two..." -- putting out 165k BTU.

Assuming that the furnace(s) and the water heater share a chimney,
there should be no problem with the chimney being warm enough for a
good draft. OTOH, those furnaces have got to be sucking a huge
amount of combustion air out of your house, making a backdraft down
the chimney very likely.

Despite the house being old, I suspect those Pella windows have
reduced the available amount of makeup air significantly.

If you replace the furnace(s), you might consider a high-efficiency
unit that obtains its combustion air from outside the house and
vents through the wall. That will eliminate the furnace as the
source of any backdrafting. But then the water heater will be the
only user of the chimney, which may then be too large, so you may
yet need induced draft for the water heater.

You may also be able to install in the furnace room a makeup air
vent to the ouside that opens only when the furnace is on.

Sounds as if you have a good HVAC tech who knows how to do heat
loss calculations. Get him and your chimney sweep to advise you.
Unfortunately, some trial and error goes with this process. In the
mean time, keep a close eye on your CO detector.

--
Doug Boulter

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