Fireplace is sending bad smoke signals

Q Our house has a wood-burning fireplace in the living room and another in the family room in the lower level. Why do we smell smoke in the lower level when the fireplace in the living room is going? What can we do about it?

A The upstairs fireplace probably isn't drafting properly. Most likely there's so much air going into the fire and up the chimney flue that so-called makeup air is being pulled down into your lower level by the other fireplace flue.

To better understand what's happening, think of the wood-burning fireplace as a large exhaust fan. With a roaring fire, it's able to expel up to 450 cubic feet of air per minute from your home. For every cubic foot of air that leaves the house, a cubic foot of air has to come in to replace it.

That can present a problem in tight homes, and research shows that Minnesota homes, old and new, are often tighter than many people assume.

What ends up happening is that other openings in your home, including the adjoining flue, provide the makeup air supply. The adjoining flue probably captured some of the smoke, which is why you could smell it. It also likely carried carbon monoxide (CO) into your lower level. That's a real safety concern. It's important that you have a CO alarm in the rooms with the fireplaces. Better yet, have this situation resolved before using the fireplace again.

To help do that, start by reading the state's free publications "House Diagnostics" and "Combustion and Make-Up Air." (Call 651-296-5175 or 1-800-657-3710, or download free copies at www.energy.mn.gov.)

Then consider hiring a specialist to measure air leakage in your home and the interplay of the fireplaces with other fuel-burning appliances in your home (water heater, furnace and clothes dryer). Members of the Minnesota Building Performance Association, www.mbpa.us, a nonprofit professional trade association, can provide a list of members for these diagnostic tests.