Creosote is a flammable substance that is hard, dark, and crustlike. It is produced during incomplete combustion of wood. An accumulation of creosote can cause a dangerous chimney fire, so it must be removed.

• You can minimize creosote by burning dry hardwoods, since their lower moisture content promotes more complete burning.
• A hot fire produces less creosote than smoldering woods. Increase the air supply if necessary so that wood burns more completely.

Identifying Soot
Soot is a flammable deposit, dark in color but softer than creosote. Most chimney sweeps recommend cleaning when soot deposits reach 1/8-inch in depth.

Creosote Glaze
This shiny, tar-like product is flammable, and usually difficult to fully remove.