After heavy rain, water pools around our basement furnace. After climbing onto the roof, I found a mysterious (plumbing?) vent.

This post seemed relevant, but 0.5 gallons comes in after a good rain. It seems more than just a flashing issue.

There are 2 such vents on the roof, in addition to the original chimney.


  1. Would putting some sort of cap on top of the vent fix this?
  2. What would such a cap be called?


  • Q: What would such a cap be called? A: Hole where the rain comes in ... If this were my roof I'd definitely put a cap over the end of that.
    – brhans
    Aug 24, 2019 at 1:09

2 Answers 2


This looks like a newer “vent “ & exhaust, I haven’t seen one quite like that but it looks like a coaxial vent & air supply for a closed system. I wonder if it is rain or a plugged condensate drain that is the problem because that small area would require much more rain to provide what I think you reported even at biblical proportions, I don’t think it has rained that much in our life times. So will a cap help , maybe but probably not. A hvac pro can probably find a problem in short order but I don’t think it could be rain.

  • The water only appears after heavy rains, which made me assume it is not condensation. Aug 24, 2019 at 13:43

Once winter concluded, I finally noticed that the water was trickling in through the basement wall due to poor grading outside the house. I thought the water was coming FROM the furnace and spreading elsewhere, but in reality, the water was coming FROM the wall and spreading to the furnace and elsewhere.

After a heavy rain, I put on a headlamp and closely watched little particles in the water moving towards the furnace.

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