Chimney Overheated or on Fire

Problem: Fire in fireplace or wood stove overheats chimney or ignites fire in chimney, accompanied by a loud roaring sound.

Background: A common cause of fires is the over-firing of a stove or fireplace, so that it becomes over heated. This often is the result of building a fire that is too large or too hot. Another cause is an internal fire in the chimney, resulting from an accumulation of soot and tar inside of the chimney. Often internal chimney fires are accelerated in high-efficiency stoves that have controlled drafts and a limited air supply. The build-up is highly flammable and may ignite. Chimney fires can be frightening, and temperatures in side the chimney may reach up to as high as 3,000°F, creating a tremendous updraft that causes a roar.

What to do: The average chimney fire has a duration of 5 minutes or less. Unfortunately, other than calling the fire department, not much can be done during a chimney fire. Extinguish the original fire, if possible. (Some experts suggest dumping large amounts of coarse salt on the fire, then holding a wet blanket over the hearth opening to keep air from entering the chimney.) Do not run water into the hot chimney because this may crack the flue liner or bricks.

Special advice: After a chimney fire has been extinguished, the fire department will inspect your home to make sure it has not been damaged. Do not use the fireplace or stove after a chimney fire until it has been inspected by a chimney expert. To minimize the risk of chimney fires, do not use a fireplace or stove for burning large amounts of paper scraps or wrappings, corrugated boxes, wood shavings, Christmas trees, or wood that contains flammable adhesives (such as plywood or paneling). These materials can burn at temperatures high enough to make chimney damage likely. As a general rule, don’t use more than three or four full-sized logs in your fireplace or other wood-burning device, and have the chimney inspected and cleaned regularly.

Helpful hint: Chemical cleaners can be used to help inhibit soot build-up. (Common rock salt, thrown into the chimney, will not do the job.) Deposits in a chimney can vary from soft and fluffy ash to rock-hard, almost crystalline material. Consider hiring a professional chimney sweep to do the job.