Schedule regular cleanings by a
chimney sweep if you use your
fireplace often.

Understanding Creosote

When wood burns, it produces water vapor, gases, and smoke. Ideally, all these are swept up the flue and out the chimney. However, as these warm vapors reach the upper parts of the chimney they encounter the cooler outdoor air and condense, forming creosote.

Creosote is a black or brown residue that clings to the inner surfaces of the flue liner. It can be hard and glassy, sticky, or even dry and flaky. When creosote builds up in a flue, it may catch fire. Although new flue liners must be rated to withstand 1700-degree temperatures, a flue fire can reach 2,500 degrees. Should a flue fail in a fire, the nearby wood framing members and insulation in a house can ignite.

Flue fires can be insidious events. A small hot spot can smolder for hours after the fire in the firebox has been safely extinguished. Hidden in the chimney, a fire can build and spread throughout the flue undetected.

That's why, in addition to removing soot and other debris from a flue, be sure all creosote is removed every time the fireplace is cleaned. Remember, too, that chimney sweeps see a lot of fireplaces and flues so their eyes are better trained to recognize the difference between creosote build up and plain soot.