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Community and Q&A

Chimney downdrafting

kjmass1 | Posted in General Questions on

I have a 1940’s home that is insulated well with new windows, and we find we get a pretty strong downdraft down the chimney when it rains or there is a pressure disturbance. I’m sure the flue door isn’t that great but there is a aluminum cap on top.

I’ve been keeping a window cracked in the hopes it pulls air from there instead although now in the summer that doesn’t seem like a great idea. I’ve seen balloons you inflate but I can’t imagine those defy physics of air pressure and temperature drops.

What’s the underlying problem? I can’t imagine I’m the only one with this problem and the House certainly isn’t as tight as the ones on this site.

We do have a pro range hood, and use only one bathroom fan each morning. Is it as simple as opening an attic window? Basement is uninsulated, and we have steam heat as well as split ac/heat pumps.


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  1. GBA Editor
    Martin Holladay | | #1

    Please describe the chimney. What does it serve? A wood-burning fireplace? A wood stove? A furnace?

    Or perhaps the chimney is unused. We need to know if the chimney is in use when this happens.

    The solution will depend on what the chimney is used for.

    It's certainly true that if your house has exhaust fans, the makeup air has to come from somewhere -- and the most obvious hole in your house allowing makeup air to enter may be your chimney. For more information on this issue, see Makeup Air for Range Hoods.

  2. kjmass1 | | #2

    Thanks Martin. It is a wood burning fireplace, I probably burn less than 1/2 a cord per winter. Strictly for ambiance. It does need to be cleaned this year but I believe the issue would still arise regardless.

    I can’t recall the issue happening in the winter all that much...probably because heat is leaving up through the chimney.

    I will say when it does start to smell it’s an all day thing- not just when the exhaust fans are running.

    I’ll take a look at that link, thanks.

  3. GBA Editor
    Martin Holladay | | #3

    Sometimes this type of downdraft can occur due to a combination of wind and the Venturi effect. A chimney balloon would help in that case.

    If the downdrafting is associated with the use of your exhaust fans, however, you may have a makeup air problem.

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