Creosote and Chimney Cleaning for Wood Stoves
Have a wood stove's chimney inspected and cleaned every year by a professional. That is the U.S. Fire Administration's advice, and the reason is creosote: tar and soot that condense from smoke on the inside of a cool flue and can catch fire.
Where creosote comes from
Smoke is unburned fuel. When it reaches a flue that is cooler than it is, part of it condenses into a sticky or flaky deposit. Two habits make far more of it:
- Burning wet wood. University of Maryland Extension says wood above 20% moisture gives less heat and raises the risk of a chimney fire from creosote. Steam from wet wood cools the smoke. See how to season firewood.
- Smouldering. A stove that is too big for the space gets turned down to keep the room bearable and burns slowly and smokily. The stove size chart matches maker ratings to floor area so you can avoid buying more stove than you need.
Newer EPA-certified stoves burn cleaner: the May 15, 2020 limit is 2 grams of particulate an hour (see EPA wood stove rules), but no stove is creosote-free when fed wet wood.
The numbers behind the advice
The USFA reports an estimated 32,200 home heating fires in the United States in 2021, causing 190 deaths, 625 injuries and $442 million in property loss, and heating remained the second leading cause of home fires. Its prevention list for wood heat is short:
- Clean and inspect the chimney and stove every year, by a professional.
- Keep anything that can burn at least 3 feet from the stove.
Look up a certified chimney sweep near you before the season starts; booking in late summer is easier than in the first cold snap. Cord Calc does not list or refer sweeps.
Signs to call before the annual visit
- A layer you can scrape with a fingernail on the inside of the stovepipe.
- Smoke rolling into the room when the door is opened, or a fire that suddenly will not draw.
- A roaring or rumbling from the flue, or flakes of soot on the roof: these can be a chimney fire. Close the stove's air controls, get everyone out and call 911.
Sources
- U.S. Fire Administration, Heating Fire Safety (last reviewed 2023-05-04).
- University of Maryland Extension, FS-937.
- 40 CFR 60.532.
Questions
How often should a wood stove chimney be cleaned?
The U.S. Fire Administration says to have chimneys and heating equipment cleaned and inspected each year by a professional.
What causes creosote?
Smoke that cools and condenses in the flue. Wet firewood and fires turned down to smoulder make more of it; University of Maryland Extension notes wood above 20% moisture raises the chimney-fire risk from creosote.