What Causes Chimney Fires?

Learn how to prevent chimney fires using this detailed guide that will help any wood burner work more efficiently and safely. Once you know what causes a chimney fire, you will be prepared to prevent one.

By MOTHER EARTH NEWS Staff
Updated on September 9, 2022
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by AdobeStock/photosampler

Learn how to prevent chimney fires using this detailed guide that will help any wood burner work more efficiently and safely. Once you know what causes chimney fires, you will be prepared to prevent one.

What Causes Chimney Fires?

One of the true challenges of parenthood is facing questions like, “Mommy, where do the pieces of tree you put in the woodstove go?” What do you say? Do you launch into a speech on oxidation of carbon, vaporization of water, temperature-induced draft and flue gas velocity? Might as well invoke gremlins. A more honest and effective answer would be to explain that much of the wood turns into goo — a substance resembling day-old oatmeal, except it’s black — that sticks to the inside of the chimney.

That glop is, of course, creosote, the wood burner’s bane. It’s a nuisance to clean out and a hazard to leave alone. Touched off by the right combination of heat and oxygen, creosote can show a demonic mind of its own, turning a normally smoky chamber into an inferno. Flame temperatures in a chimney fire can exceed 2,000 degrees Fahrenheit, sufficient to crack a flue liner or send showers of sparks onto the roof. More than 20% of all house fires are caused by woodburning appliances, and around half of those are related to chimney problems.

What Is It?

Creosote consists of particles and condensed vapors left over from the incomplete combustion of wood. It comes in many different forms — chimney sweeps identify types such as tar glaze, slag, flakes and soot — but all are combustible. Besides posing the threat of chimney fires, creosote is messy; it stains pipes, connectors, chimneys and roofs and corrodes metal parts of the chimney system. Some of its constituents may be highly carcinogenic.

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