Air Quality

Published on June 4th, 2013 | by Henri


Fireplace smells when windows are closed

Q.    I need your help. We use our fireplace very often in the fall and winter months. The problem that we have is the smell during the months we don’t use it. Often we get a smell of burnt wood when it is not in use, especially when we have our exhaust fan in the attic or bathroom on. The smell only goes away when we open a window.

Sometimes the smell is so powerful we must turn the fans off. We have had the liner in the chimney replaced, and have it cleaned every year before we use it. Also the brick on the outside of the fireplace is very black, leading us to believe that a chimney fire may have occurred. What can we do to get rid of this smell?

A.    Warm, moist air is drawn out of the house through the fans — and exfiltrating through cracks and crevices around windows and any other vulnerable components on the upper floor. It all creates a negative pressure inside the house. Nature abhors unbalance so the equilibrium is corrected by outside air racing down the chimney — the easiest make-up channel.

When you open a window, it makes it easier for the make-up air to be supplied, and air either no longer comes down the chimney or is so diminished as to no longer be a problem. You can reduce the smell by closing the fireplace damper when you are not using the fireplace (and you know that the fire is absolutely dead) and by installing tight glass fire doors. And since it appears as if your house is tight, open a window whenever you use one of the fans.

You may also want to try spraying all your firewood with ACS, a catalytic solution that prevents the build-up of creosote on chimney walls and cleans it off if it is present. This should help a lot. You should be able to buy ACS in stove shops or through chimney sweeps. You can also buy it on the Internet at:

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