My basement takes on water from time to time. Usually during/after rain, and sometimes snow. It's a slow trickle, but it can last for days.

It appears to be coming through the wall, right under the chimney cleanout door.

With heavy rain, I can sometimes vacuum 2-3 gallons of water out at once!

It's worth noting that I removed all water in the chimney and the basement yesterday evening. Then it rained this morning. Yet when I got home this afternoon, the basement had lots of water, but the cleanout had only a half-inch of water. Either the chimney completely emptied into my basement, or the water actually came in from somewhere else.

I've only been here for a few months, I don't know how long this has been happening.

The chimney clean-out door is in the upper left corner of this photo:


Yes, I'm 100% sure it's not coming from the water heater. If I keep wiping the water up, it only comes from the chimney wall.

Close-up: Chimney clean-out door

Here's the bottom after emptying the water:

Bottom of chimney cleanout

I can't pin-point the exact place the water is coming in the basement. It may be where the wall meets the floor, or perhaps the wall itself? But the wall doesn't seem as wet as I would expect for this much water. The water level in the cleanout when I go to vacuum it is typically halfway to the bottom of the door, so I don't think it's just spilling out through there.

There is no fireplace. I am not sure if there ever was... There is just a bedroom there on the first floor, just drywall, no sign of there ever being a fireplace. The house is from the early 60's.

I especially don't think there was a fireplace because the chimney seems to be a straight shot:

Inside chimney looking up

There is no chimney cap. Everyone else on the block seems to have one.

Below is a diagram I found and modified for my chimney removing the fireplace and making it straight, then adding a furnace.

Chimney diagram

What could cause this, and how can it be fixed?
Could the lack of a chimney cap actually cause gallons of water to fill in the cleanout? Would it be more likely that water is actually seeping into the cleanout from below the ground? If so, is that something an inexperienced person should attempt to fix?

Note that I can't really go on the roof yet, as it is still icy. I was going to wait for spring, but the leaking worries me about further damage.

  • 1
    a US gallon is 231 cubic inches .... if your flue is 12"x12", then 1.6" of rain will dump a gallon of water down the chimney
    – jsotola
    Commented Feb 21, 2018 at 23:13
  • use a plumber's putty, or even play-doh, to build a dam on the floor around the cleanout door area .... move the shelves out of the way and make the dam around a fairly large area ... that will narrow down the area where the water is coming in ...
    – jsotola
    Commented Feb 21, 2018 at 23:22
  • tap on the sides of the flue on the cleanout area. ... see if it sound hollow
    – jsotola
    Commented Feb 21, 2018 at 23:25
  • @jsotola - Tap where exactly? And what would it being hollow tell me?
    – Bort
    Commented Feb 21, 2018 at 23:36
  • reach in through the cleanout door and tap the flue lining everywhere you can reach. ... a hollow sound would mean that there is a void, maybe as a result of improperly poured concrete ... the void, if any, may extend close to the outside of the foundation wall
    – jsotola
    Commented Feb 21, 2018 at 23:42

3 Answers 3


I added a chimney cap, and the leaking was significantly reduced during rains.

Chimney Cap
(Image from http://Lowes.com)

I later noticed that during rain, water was pooling on the ground near the chimney. So I built up soil against the base of the house. This made the rain water run down and away.

After both fixes, there is no longer any water leaking in, even during heavy rains!


Using modern programmable thermostats do not allow long runs of furnace which causes lots of condensation in chimney. I figured this out on my 60 yr old home .. Allow longer burns although more temperature variance in house to my surprise not only fixed the problem .. I USE 1/3 LESS FUEL.. !!!!


Of course you’ll want to line/vent/cap it when you can, but if you can’t do that yet, and have reason the believe the water may be coming from below, you could test it (assuming you’re not currently using the chimney to vent appliances) by inserting a chimney plug/inflatable draft stopper just above the cleanout door and watching the water. If the water builds up on top of the plug after it rains you’ll know it’s coming from above.

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