Why Is Charcoal Burnt in the Hearth?

Identification

• The black substance found inside your chimney is not charcoal, but a substance known as creosote, which is a tarlike substance that is caused by burning natural wood. According to the University of Arizona, creosote forms when flammable gases that occur when burning wood cool below 250 degrees F. Once cooled and dry, these gases thicken into a flammable substance known as creosote.

Hazards/Causes

• When creosote becomes thick inside your chimney, there is a risk of fire. Creosote will ignite when temperatures are hot. A chimney will crackle when burning, which is caused by creosote deposits on the chimney wall. If creosote is thickly coated in your fireplace, it may ignite and produce a roaring noise. Once a fire starts, it can cause flames to shoot out the top of the chimney, landing on the roof and causing it to catch fire. Homes or buildings in close proximity to a chimney fire are also at risk of sparks and fire.

Prevention

• Slow, long-burning fires cause more creosote than hot fires. Burning green woods cause more creosote to build up in your fireplace than burning hardwood. Avoid burning wet wood in your fireplace to prevent excess creosote buildup. Certain types of wood produce more creosote as they burn. Dry oak and juniper produce less creosote than pine.

Solution

• Allow your fireplace to burn frequent, high-heat fires to remove creosote deposits from your chimney wall. These fires do not need to burn for long periods of time; a brief hot fire will do the trick. Before using your fireplace each year, remove creosote deposits that accumulated the previous winter. Scrub creosote deposits away with a stiff wire chimney brush. Clean again if creosote becomes 1/8 inch thick on your chimney wall.