Help with correct furnace exhaust PVC


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.
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Can't you drill a very small hole at the low spot of the belly, is it in a place where yhou could run to a floor drain
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I am trying to fix the problem, not create more.
I don't think drilling holes in an exhaust pipe is a fix..

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Homebrewdude wrote:

You are sure right about that.
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theedudenator wrote:

The fan should have a drain port & tube running to the drain, make sure that is not plugged with goo.
MikeB
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I am looking into that also. I do not have a manual for the furnance and Armstrong does not have much on its site.
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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.

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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.
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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 again.
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theedudenator wrote:

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.
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Might need to put a 45 degree angle piece on the exhaust, to help shield from rain.
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Stormin Mormon wrote:

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.
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I would think it should angle to drain outside or what about rain.
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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)
cheers
Jules
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Jules wrote:

That's certainly not true here in Seattle. There do have to be certain clearances from openable windows, doors, or air intakes.
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On Mon, 02 Nov 2009 14:28:53 -0800, Bob F wrote:

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.
cheers
Jules
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Jules wrote:

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.
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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.
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theedudenator wrote:

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 handy.
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theedudenator wrote:

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 pipe.
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