Q: I live in an 18-year-old condo in San Mateo, Calif. It is on the top floor of a three-story building. When the condo just below me has a fire in the fireplace, I get noxious fumes–like when a candle has been snuffed–that continue as long as the fire lasts. The chimney pipes are separate but side by side and the same height. What should I do?

A: Danger! When was the last time you or your neighbor had your chimney inspected or cleaned by a chimney sweep? Over 18 years, both fireplaces probably have seen many a winter fire. It’s likely that you have a wood-burning zero-clearance fireplace with a triple-walled metal chimney. These units have been installed for many years as an economic alternative to brick fireboxes and masonry chimneys. Like their masonry counterparts, they require periodic cleaning and maintenance. The most likely cause of your problem is a dirty chimney. After years of wood fires, creosote builds up in the chimney.

As wood burns, it releases heat and gases containing tiny airborne particulates. The gases escape to the outside through the chimney, but some of the particulates adhere to the chimney walls, forming a substance called creosote.

Over time, the creosote buildup becomes combustible. As a fire burns, the creosote in the chimney starts to smolder, releasing more gases. Because your chimney shares the same chase as your neighbor, it’s possible that a leak at one or more of the joints in the chimney pipe is allowing some of the combustion gas into the chase. These gases may then be entering your home through openings such as electrical boxes.

Chimney fires resulting from creosote buildup are very dangerous. We suggest that you tell your neighbor about your observations. Then, assuming that your chimneys have not been cleaned or inspected recently, have it done.

Look in the Yellow Pages under “chimney sweeps” to locate a tradesman who can perform this service. We suggest that you also call your local fire department and ask it to do a safety inspection. There should be no cost for this service.

Another, less likely, cause of the odor might be the weather. Assuming that you are not operating your fireplace at the same time as your neighbor, you may be getting some back draft from the smoke exiting your neighbor’s chimney. This can occur on a calm day when the humidity is high. Unless you notice the smell only occasionally, it’s unlikely that this is the cause.

Bill and Kevin Burnett will attempt to answer your questions although the volume of e-mail sometimes makes this impossible. Contact them at sweat-equity@comcast.net.


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