On the utterly useless ng alt.hvac, reference was made to a lennox 90%
furnace not working in a very cold attic, that some drain was freezing up,
causing the furnace to malfunction.
What needs to be drained in an attic furnace? In ANY furnace?
I have a furnace with a dehumidifier whatsits, and no drain.
The only drain on my furnace is for the A/C condensate.
And also, what exactly is malfunctioning and why?
Is it your furnace, or someone being abused at alt.hvachackforabeer,
the drain on a condensing furnace cant freeze.
I guess Google is my friend:
http://en.wikipedia.org/wiki/Furnace is a good article, explains condensing
Actually, it was a mechanic posting. They don't abuse other ""tradesmen"",
just home-moaners. When a tradesmen posts, they figger they have another
participant for their circle-jerk.
Here's the thread:
Yes it is a little hacky, I thought it might have been freezing in the trap
too, that's why as I mentioned we insulated and put heat tape on the trap
and drain line thinking that woud solve the problem, but it didn't. I think
something is freezing in the furnace itself.
So, they seem to agree that some water is freezing, just not as to where.
Since I don't think the system would really care if condensate is freezing
or not, mebbe it could be a lockout sensor for flue gas temp, sort of like
I'm a little hardpressed to figger out what a furnace is doing in an attic,
as well, but that's another story.
High efficiency furnaces cool the
exhaust vapors so much that water
condenses and must be drained. Much
depends on the furnace design
on where it might be freezing. I know
on my unit, it could happen in several
places, however, it won't as it is in
the somewhat warm basement (60 degrees
or higher). I have a condensate pump on
my system, and if it gets over full,
it will shut down the furnace. The
output hose did have a little dip in the
and when it froze, the heat shut down.
So, you have to check the entire
run from where it come out of the heat
exchanger/fan unit, all the way to the
place where it finally drains. I could
be anywhere. I doubt if it is inside the
furnace, as it makes its own warm
environment (when it's running properly)
and probably won't freeze, unless you
are in a really cold environment. So,
it's probably somewhere after the water
exits the box.
Well, Tony, doesn't it boggle your mind as well, that one can have a
dialogue amongst a bunch of struggling home-moaners that is 20-30x more
intelligent, informative, and productive than ANY thread in the HISTORY of
It had to have been all that freon, affecting their already assaholic
Forced air furnaces in an attic are not unusual. In many larger two
story homes they have one in the basement for the lower portion of the
house and one in the attic for the upstairs. Much easier to run the
ducting and better temp control.
In addition to what Art said, a condensing furnace should never be put
in a non conditioned (attic) area. The risk of damage due to freezing
is too high. The entire heat exchanger can be damaged if it freezes
during a power outage or even between cycles if it's off long enough.
That's news to us here in NJ where they are going in loads of new
construction. A similar argument could be made against putting AC
units in attics or bathtubs upstairs. There is always some small
risk of potential damage. But properly installed they do just
On Fri, 15 Jan 2010 07:54:37 -0500, Existential Angst wrote:
The 90% efficiency furnaces create condensation in the exhaust and it needs
to have a drain line on them. If it freezes this condensation backs up and
blocks the exhaust, creating backpressure and the temp rises, causing the
furnace to shut down.
You'd think no one has ever heard of heat tape. When I install
a walk in freezer, I install electric heat tape on the drain
pipe. The same stuff will work on the drain line of a condensing
furnace located in an attic or a utility room that is unheated.
It's a simple problem to cure with off the shelf products.
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