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Elisabet

Gurgling sound from furnace exhaust pipe

5 posts in this topic

Last week I was visiting my mom, and as I was sitting in the kitchen with my coffee one morning I heard a gurgling sound coming from the "basement" - really a ground level room a few steps down from the kitchen. It was loud, in fact at first I thought the washer was running.

Upon investigating I discovered that the loud gurgling sound was actually coming from a pvc pipe that attached to the furnace (gas powered). It comes out of the funace, goes up a few feet, then runs horizontal a few feet then continues vertical through the ceiling. I'm pretty sure it lines up with the furnace chimney (which does have a cap) that I can see poking out of the second story roof on that part of the house. It's a big old house, with a big old furnace, A/C and a mix of many decades worth of ducts and equipment. I think the current furnace is about ten years old and the pvc was not there when I was kid; guess they used metal back then.

I'm guessing that the source of most of the water is condensate from the exhaust, not rain, since there is a rain cap on the chimney, and it sounds like there is quite a bit of water in the pipe. The horizontal run of that pipe is tied to the ceiling but there is some play there, and though I didn't check it with a level due to the water collecting in that spot it does seem that there is a slight dip to that second elbow.

It might be possible to push that elbow up a tiny bit and run the water back, but dumping water into the innards of the furnace didn't seem like a good idea so I left it alone. There is no valve to drain the water, either, everything is glued up.

Yes, the gurgling sound happens if and only if the heater is running.

question:

Is water in the exhaust pipe a problem? Or just a noisy nuisance? The exhaust does seem to be gurgling out in spite of the water. Is this normal behavior for a furnace?

Thank you for the help, oh wise ones...

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what diameter is the pvc pipe?

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Look around where the pipe exits the furnace, you should see a small tube that either goes into a drain or a sump hole.  This is the condensate drain line that allows water to drain from the exhaust.  With the furnace running you should see a small amount of water coming out.  If your furnace is a high efficiency model than there most certainly should be a drain line below the exhaust.  If water gets back into the furnace it will cause corrosion and premature breakdown.  Have your furnace inspected if you are not sure what to look for.

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Unfortunately I'm several hundred miles away from the problem now - but I think the PVC pipe was a few inches in diameter. Not as big as e.g. a sewer pipe, but more than an inch.

There is a condensate drain line - at least I assume that is what it is - 1" pvc but I couldn't see exactly where it went; under the stairs to the crawl space under the house. So no idea if there was anything draining from it while the furnace was running. It was not connected to the exhaust pipe that I could see; came out the other side of the unit. I assumed it was for the A/C. (Never noticed our drain line producing anything when the furnace is running, but it's a very different set up).

Sorry to be so vague.

Is it ok to have the exhaust pipe take a horizontal run like that? And I take it that getting that much condensation means there is a problem with the furnace or the installation. Sounds like my mom will have to have a service call.

Thank you

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that line probably needs to be inspected to see if its draining properly

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