The smell of smoke lingering in a firebox after the fire is out may indicate a drafting problem or a dirty chimney.

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Q: We have a wood-burning fireplace that we use only a couple of times a season. For two or three days after it has been used, it emits a strong “smoky smell.” The fireplace has glass doors that we keep closed, and we remove all the ashes from the firebox after burning. We have not been able to correlate the problem to outside air pressure or outside temperature. What causes this smell? How can it be eliminated, or prevented?

A: The odor is from creosote. Your chimney may need cleaning. But it also could be that your chimney is having trouble drafting, due to creosote buildup or pressure imbalances within the house, rather than outdoors. Such imbalances typically occur when an exhaust fan is on in the kitchen or bathroom, or appliances such as the dryer, furnace or water heater are working. The air they push out of the house is greater than the amount of makeup air that can leak in through random cracks and holes. The result is that makeup air is pulled down the chimney, which is a big, unrestricted hole in the house.

If that happens when you have a fire going, smoke will fill the room. But when there’s no fire, you may notice only what some homeowners describe as a “smoky odor” from the fireplace. It’s important to know what is causing the drafting problem and to fix it.

One other possibility is that a fault has developed in your chimney or flue, said energy specialist Phil Smith at the Minnesota State Energy Office. It may seem as if the odor is coming from the hearth, but it’s actually leaking out higher around the brick and mortar chimney.

In any case, you’ll want to have a fireplace expert take a look at your problem. That could be a certified chimney sweep or a fireplace construction and repair firm. Look for them in Yellow Page directories or ask at a store that sells wood-burning fireplace supplies. Ask the person if he or she can address household depressurization issues, too.

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