The Deal

• $99 for a full inspection and chimney sweep ($199 value)

Five Things to Know About Creosote

A chimney cleaning clears the flue of creosote—a black or brown substance that builds up over time. Learn why it needs to go with Groupon’s breakdown.

1. Creosote comes from condensation. As wood burns in a fireplace, it releases a veritable cocktail of materials: smoke, water vapor, tar fog, and a number of gases. These substances move up the chimney, cooling and condensing as they rise. That condensed stuff sticks to the sides of the chimney in the form of a black or brown goo—sometimes sticky, sometimes flaky, and always highly combustible.

2. It can be dangerous if left to linger. Due to its flammable nature, creosote is the number-one cause of chimney fires. These blazes can range from small, undetectable smolders inside the chimney itself, to five-alarm catastrophes that can level a house. Fortunately, routine cleanings are a very effective way to prevent fires.

3. Creosote can be good, too. Both man-made kinds of creosote—wood-tar and coal-tar—are toxic, but they’re also manufactured commercially due to several benefits. The wood-tar variety helps preserve wood structures and Trojan horses, while the more noxious coal-tar type makes a good sealant for railroad ties and bridgework.

4. Not all creosote is man-made. Larrea tridentata, a low-growing, spiky plant commonly found in deserts, is known as the “creosote bush” for its pungent smell. Native American tribes of the Southwest used the plant’s leaves in teas or compresses to treat minor ailments such as bruises and colds.

5. Don’t invite creosote to your barbecue. Creosote can build up on roasted meat the same way it accumulates in a chimney, resulting in a bitter, unpleasant taste. A small amount, however, can keep meat from rotting—in fact, the name derives from the Greek words kreas, meaning “flesh” or “meat,” and sōtēr, meaning “preserver.”