I get the ashy fireplace smell in the family room when the A/C is running. I haven't had a fire burning in months.

I checked out this question, but it targets a recent fire and a cold air return.

It would seem that I'm getting negative pressure in the house when the A/C is running, being equalized through the fireplace. I have a Buck Stove insert that was there when we bought the house. Consequently, I don't have the standard flue closure mechanism. It's more of a stepped closure to control airflow while the stove is burning.

Is there anything I can do to prevent the negative pressure that comes with running the A/C?

  • Are you sure it's negative pressure? A/C doesn't cause negative pressure like exhaust fans or dryers do. Could it just be the cold air return in that room is 'over zealous' ? You might experiment by blocking the nearest return off.
    – HerrBag
    Jun 12, 2013 at 22:03
  • @HerrBag, The thing is, the smell is really only in that room, so I don't think the actual ventilation system is actually involved. At least, that's why I surmised it was a pressure thing.
    – JoshP
    Jun 13, 2013 at 0:41

1 Answer 1


One way would be a Heat Recovery Ventilator(HRV) that exchanges interior air for outside, which will relieve negative pressure.

Another would be a dampered (and screened) make-up air that connects to the cold air return (a low tech (and low cost) HRV). These can be tied to exhaust fans or automatic via pressure differential. You would want a HVAC firm to discuss options.

A third would be a cable operated chimney cap damper. The stove may complicate this option. I had one on a naturally aspirated fireplace and was good during rain and windy conditions that used to produce that "old fire" smell.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.