landscape contractor Roger Cook
Q: Our three-year-old chimney is cleaned twice a year, but we've already had a chimney fire this year. Is the chimney not being properly cleaned?

—Nanci Davidson, Chicago

A: Tom Silva replies: Chimney fires are fueled by highly flammable deposits of creosote that build up bit by bit as warm smoke condenses on the sides of a cold flue. These fires are dangerous; they can burn hot enough to melt mortar, ruin a flue, and increase the chance of a house catching on fire. Here are some things you can do to keep creosote in check.

• Only burn wood that has been seasoned for at least 12 months. It burns cleaner, and its drier smoke won't condense on flue walls as readily as the smoke from green, unseasoned wood.

• Maintain a good draft. If smoke backpuffs into a room, it's probably lingering too long in the flue. Talk to a mason about ways to increase the flow of makeup air into the fireplace.

• Install a damper at the top of the chimney. These dampers, controlled by a cable that leads down to the firebox, help the flue stay warm between fires, reducing condensation problems.

Even if you're doing everything else right, creosote will build up if your chimney isn't being cleaned properly. So make sure your sweep is licensed, insured, and a member of a recognized trade association, such as the National Chimney Sweep Guild. Unaffiliated, fly-by-night sweeps do a better job of taking your money than keeping your flue clean.
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