I have an exhaust vent in my basement (Amerivent Type B) which takes the exhaust from my gas furnace and water heater goes out the basement wall, and up my chimney. A little bit water is coming in to my basement from this vent. It looks like this has been happening for quite a while based on drip marks on the floor (since before I moved in in 2007) but it recently lasted long enough to run back along the pipe and into my furnace, shorting it out.

I took off the vent from the furnace and reached in there, there's a little dampness where it turns 90 degrees to go up the chimney but none before that making me think it might be a small leak at the top of the chimney but the amount is small enough that it could condensation (if the water heater exhaust could cause condensation).

Can/Should I fix this or just leave it as the previous homeowners did? How can I prevent it from running back into my furnace again (seemed to go between the inner and outer wall of the vent pipe)?

Edit I shined a flashlight back there and it looks like some leaves had built up.


I took care of them with a shop vac. Will that take care of my problem (until the next time they build up of course)?

  • 2
    It sounds like your chimney is missing its cap - do you see a cap on the top of it?
    – Steven
    Mar 31, 2012 at 15:09
  • It looks like it's still there. There's one for smoke from the fireplace and one for this exhaust pipe. Both look fine from the ground. Mar 31, 2012 at 15:56
  • I'd say the next step is to go up on the roof and check it out. Maybe a bird or animal got in there.
    – Steven
    Mar 31, 2012 at 15:57
  • 1
    re: leaves, you should also be able to find screened caps (useful for keeping birds/squirrels out...yes, squirrels have been known to fall down them. I know from experience. )
    – DA01
    May 2, 2012 at 19:20

1 Answer 1


While looking at the cap, it's probably worthwhile taking a look at the caulking between the crown and your flue, and or flue-cap, which may have eroded. This needs to be looked at about every year or two (more or less frequently depending on your local habitat, but both extremes in hot and cold weather will help age caulk, rot brick, etc.)

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