Smoke in Basement

waytoobusyDecember 4, 2012

Hoping someone can provide us with some insight/suggestions. We've had a chimney sweep/repairman out to help and he capped the flue but had no further ideas.

50 year old home, We have a fireplace on main floor venting into a chimney that runs side by side with an old furnace flue. The old furnace was replaced and is now exterior vented through the cellar wall and the old furnace flue in the chimney has been capped. Since the new furnace was installed, there is a good deal of smoke that flows in to the basement thru the furnace cleanout every time we have a fire.
There is no smoke on the upper floors of the house. The exterior chimney is in good repair.

Could there be an air exchange between the flues inside the chimney (maybe a broken liner?) or is this likely due to an improperly capped unused flue?

Thank you for any advice you might be able to offer.

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It's an improperly sealed unused flue. Having said that, that wouldn't happen if the stack was built to the proper height - 2-4' above the HIGHEST portion of the home, not just the part of the home where it exits. Exterior stacks (3 walls exposed) tend to make this worse with a chimney of improper height. The only solution (except extending the stack to the proper height, an expense you're not likely to undertake due to this being an unused flue) is to PROPERLY cap off the unused flue and seal it, it's not hard to do, but it has to be sealed well. Polyurethane sealant is your friend, it will last, it seals tight and sticks to everything.

    Bookmark   December 5, 2012 at 3:21AM
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I failed to clarify the sealing process in my other post - the flue needs to be SEALED tight at the BOTTOM including the cleanout w/ the poly caulk and steel. The TOP of the flue is not to be sealed, but an adequate raincap and screen need to be installed to keep rain out but allow the masonry to breathe.

    Bookmark   December 5, 2012 at 3:24AM
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You are right in your assumptions. The stacks are on the exterior and the height above the peak of the house is about 18 to 24 inches. Would we seal the bottom of the flue through the cleanout? And then seal the clean out door too?

Is it possible to have an air exchange within the stack? I suppose as long as the bottom of the flue is sealed properly, this wouldn't be a problem.

Very much appreciate your time.

    Bookmark   December 5, 2012 at 9:19AM
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No, for two reasons, the behavior exhibited and the construction of the stack. For those not very familiar with chimneys and venting systems, the problems you experience and the causes I listed don't always make perfect sense. I can assure you that they are, nonetheless, accurate. The problems are as I mentioned, and the solution is pretty straightforward.

    Bookmark   December 7, 2012 at 8:39AM
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