I have a new gas forced air furnace, Amana. The PVC exhaust
runs about horizontally 30 feet to the outside wall. PVC makes
a slight pitch back toward the furnace for draining. Everything
has worked fine until the temperature outside dropped into the
single digits. (Upstate NY) The furnace will not come on until
I go out and clean out the ice formation on the end of the pipe.
Now there is not a lot of ice, only a ridge around the edge.
What do you suggest I do to stop this? Should I insulate
the pipe so it doesnt freeze? Or should I change the pitch so
more moisture drains back instead of out? The shape of the
pipes looks like rams horns, 2 pipes up about 3 feet 12 inches
apart. Then to 180 degree fittings on top dump down opposite
each other. Should I change the outside configuration?
Read the installation instructions for the terminations of your pvc
pipes. They are very specific as to how they are to be run. Each
manufacturer has a slightly different idea on how this gets
Thanks, the installer retired. I have checked the manual and the
pipe dia and length are fine. I took a shop vacuum to both
pipes, just to be sure. Now the problem has seen to gone away.
The only thing that I noticed was there was not a screen on
the intake pipe. The manual doesn't specific any size of screen,
but shows a picture of one. Could I use standard window screen?
Or something heavier gage?
Jeff Guay wrote:
If your PVC pipes (inlet and exhaust) do not have any kind of screening at
the outside ends you are looking for trouble. Those open pipes are quite
attractive to various animals who would just love to make a home inside one
of them. After one tried, even chewed through some plastic ribs across one
of them, I covered the opening with some chicken wire to keep them out.
Go out and watch the operation of the exhaust pipe for awhile...and,
especially on a windy day. A common problem is the exhaust dumps back
on the intake pipe opening and the exhaust condensate/vapor freezes up
the intake. If this is happening, then, you need to redirect the exhaust
and/or change the intake to a more suitable position . This can often
be done by having the exhaust blow outward from the house at a higher
level than the intake pipe is , and, at 45 degrees to the house wall
for maximum distance from the intake. Refer to your furnace
That's OK about the picture. I understand you shouldn't
screen the exhaust, because it could freeze up. I like the idea
(DN B) of raising the intake pipe. The manual shows that as an
What I have done today is made a 6 inch length of foam
insulated pipe. Extended these to both the intake and exhaust.
Seems to working. I did notice in the basement the intake pipe
drips with condensation. Could this be the source of the
problem? Water going into the intake....
Jim B wrote:
Thanks. I don't have ice like those pics. There one thats
really built up, like water was running
I don't understand all the screen issues?
My ice is just at the end of the 2 inch pvc, it forms a small
ridge. Im guessing this ice is not my major malfunction...
I feel the moisture could be related to a prox switch going bad.
If when the furnace will not light, I unplug the rubber hoses to
the 2 prox switches of course power is off. Apply vacuum to
click the switch. Plug them back in. Power back on to reset. All
is well for a day or less .
So you think pulling the rubber hoses off the pressure switches and
sucking on them is the way to make your furnace work every day or two?
Could you please post your owners operation manual on that furnace
because Ive never seen those kind instructions anywhere.
Ha Ha .. thanks Bubba. just to add another twist... if I leave
the access door on the front of the furnace open a little( so it
takes in some air from basement) the furnace will run with no
problems. Does this prove that it is a moisture condensation
issue with the sensors being sensitive to moist intake air?
hehe. No, it proves that you most likely have an intake and possibly
exhaust piping error. Read the installation manual and do it BY THE
BOOK or call someone that can.
Oh yeah, one other little twist, since you are dealing with the
combustion air of the furnace and possibly the exhaust gasses of the
furnace, you might want to leave it alone since these items
incorrectly serviced can kill you and your entire family and you wont
even know it.
On Mon, 24 Jan 2005 22:57:52 GMT, TP
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