My furnace stopped working, it had some read-outs saying the exhaust
was not working.
Turns out the exhaust pipe was full of water and filled the exhaust
fan with water.
I cleaned all of this out, but now I want to correct the problem.
My exhaust PVC travels from the furnace to the outside wall. There is
a belly in this pipe. Thats were the water was sitting.
Looks like I need to have it angled to drain back to the furnace - I
need to correct the belly.
Is there a standard size for this type of pipe? Mine looks to be 3"
dia. Rather large.
I checked these and all is clear.
I do have some leaking from the internal furnace plastic part that the
drain connects too.
Not sure if it can be fixed.
Looks like the part has a manufactured split in it that is sealed.
The type of replacement pipe will depend on where you live. Some states may
have different regulations. Canadian regs. require a special grade of high
temperature PVC, identified as "System 636". Home depot carries the 2" size,
Lowes both 2" and 3" sizes. Any old equipment still running with plumbing
grade PVC or ABS are required to change the vent material if any alterations
are done to the venting.
It may even be imprinted with the size, but in any case, it is a standard
size. You can always cut a piece out and take it to the plumbing supply
with you. It is either 3" or 4" for that application. Check the furnace
manual for installation information and how much pitch the pipe should have.
PVC will sag over a long stretch. Add some hangers to keep it from sagging
Contact the manufacturer and ask them for an installation manual. IT will be
very useful now, and in the future.
It should be standard PVC sizes. You must aliminate any low spots in the pipe.
Any water that condenses in the pipe must find a slope either towards the
furnace or outside.
Could the water in the pipe have come from outside? There should be no way for
it to do that, make sure there isn't.
Actually, on mine, the installation
instructions require a 90 on the
output. I asked why. The rep said it
was to prevent wind from
causing back pressure in the combustion
area. He said this could
cause the unit to shut down. And he
said, a 45 was not
adequate because air could still blow in.
On Mon, 02 Nov 2009 04:05:36 -0800, ransley wrote:
I assume they're supposed to drain toward the furnace so that no exhaust
gas can get trapped at a high point in the system (in which case having a
pipe that bottoms out partway through might be a bad thing anyway) - it'll
always clear to the atmosphere.
Ours currently vents outside at about 3' off the ground via a 90-degree
elbow which keeps moisture out, although I think according to building
codes (we don't really have any where I am) it's supposed to vent at roof
height (which seems like common sense anyway - I'll fix ours sometime)
Yeah, I'm not surprised (I remember our home inspector did flag it when
we bought the place, too).
The other thing is that our furnace currently sources intake air from very
close to the exhaust outlet, which seems like a pretty bad idea to me. I'm
curious to know what codes in areas that have them say about that as
presumably there are recommended minimum distances (I can re-route one or
the other through the basement easily enough, but maybe I'm better off
taking the exhaust up to roof height and leaving the air intake at waist
height outside - then they have a reasonable separation but without any
basement changes). Reasonably quick/easy/cheap project, anyway...
Oh, ours is all on 2" pipe, just to add to comments for the OP.
I suspect that the furnace intake is not an issue, because the exhaust is
usually directed away from it, and there is no path that would allow intaken CO
to get into the living space. It would just go through the furnace and back out.
Typically 2 or 3 inch diameter. The pipe should slope back
towards the furnace, and there should be a drain to drain
off the water. It's normal and expected for these furnaces
to drain off a bunch of water while running. It's also
expected to get some water in the exhaust pipe.
My old Amana (1990s) used 2" all the way
out, however, newer ones
seem to have outputs of 2" or so, but
immediately up to 3". As to sloping
in or out, most seem to say that they
should slope in so the water doesn't
end up on the ground. In order to block
a 3" horizontal run, there must
be a lot of sag. But, if there is water
sloshing in the combustion fan, it
may not be the sloping (unless it is
really bad) causing the problem. In
my Amana, after about a year of use, the
drains would get plugged by
slime build up. When I removed the
drain from the fan, a whole lot of
water would come out. There was also a
drain on the secondary heat
exchanger. Its line would also get
slime balls in it and would require
periodic cleaning. A small bottle brush
with a long handle came in very
I live in Maryland and had a Carrier 92% efficient gas furnace installed
compliant with our codes 3 years ago. My exhaust PVC is supported by hangers in
the basement and slopes gently back towards the furnace so condensate will drain
back into the furnace as it should. Outside the penetration through the
foundation, they installed a 90 degree elbow facing up to the sky, with about a
2 foot length of straight PVC pipe in the open end of the elbow. Then, there is
a 180 degree elbow connected to that. This way, rain etc. does not enter the
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