I bought a house a few months ago and when I bought it I noticed what appeared to be a water spot on the ceiling of the top floor. Of course I didn't do anything about it until heavy rains over the weekend made it worse. I climbed into the attic to see what is going on and found water around the attic furnace directly above the water spot:

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From what I can tell, there is a drip tray around the furnace for collecting water, and that PVC pipe is supposed to drain it. I can see if the try or the pipe has a leak, but I'm more concerned about how the water is getting into the tray and whether it's normal for that much water to accumulate. Is anyone familiar with this setup?

  • You don't mention where you are. Have you been running the heat or the air conditioning?
    – JPhi1618
    Commented Nov 2, 2015 at 18:39
  • Do you have a high efficiency furnace with a pvc exhaust? If so, those create a lot of condensation.
    – Edwin
    Commented Nov 2, 2015 at 20:02
  • I'm in the pacific northwest United States. The AC was not running at all. And the water in the ceiling collects when it rains hard, not otherwise (I poked in the ceiling and let the water collect in a bucket in my bedroom, and it's dry unless it's been raining).
    – Cameron
    Commented Nov 3, 2015 at 19:13

2 Answers 2


If condensation can be ruled out, and it only leaks when it rains, is it oil or gas fired? If yes, then it most likely has a chimney, and probably a metal one. Depending on your roofing material you should have someone look at the flashing around the chimney.

  • It was a plastic chimney and it had cracked. They replaced it but there was still a leak...turned out to be the flashing around the chimney.
    – Cameron
    Commented Dec 4, 2015 at 22:26

I'm sure the experts will chime in and possibly correct me and/or my terminology, but that looks like a condensation tray. And it's intended to catch water from your AC unit. It looks like your tray has some gunk and debris and it's possible that this stuff has clogged the PCV pipe.

If you're sure this isn't coming from a leak in the roof, I would guess the leak is caused by the condensation due to the humidity from the rain.

If you can maneuver for access, you may be able to fit a shop vac on the end and suck/blow out the pipe.

-- Regular Homeowner

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