Creosote and chimney fires: how they start and what to do

Updated November 10, 2026 · KeystoneProGuide editorial team

What is creosote?

It is what wood smoke leaves behind in a chimney. The Environmental Protection Agency describes the process: smoke rising into the cooler flue can condense and stick to the inside walls, forming a highly combustible black or brown residue. If enough of it builds up, the agency says, it could cause a chimney fire.

CSIA, the trade's certification body, lists what is in the smoke before it condenses: water vapor, gases, unburned wood particles, hydrocarbons, tar fog and minerals. The deposit takes several forms. It can be crusty and flaky, or tar-like and sticky, or shiny and hardened, and CSIA says all of them can occur in one chimney and all of them burn.

How common are chimney fires?

Common enough to dominate the heating-fire figures. The U.S. Fire Administration counted an estimated average of 34,200 heating fires a year in residential buildings from 2017 to 2019, and found that fires confined to chimneys, flues or fuel burners made up 77% of them. Heating was the second leading cause of residential building fires, after cooking.

Most of those confined fires stay inside the flue. The ones that escape do much of the damage: the National Fire Protection Association reports that the larger fires involving fireplaces or chimneys were 6% of home heating equipment fires in 2020 to 2024 but caused 19% of the direct property damage.

What makes creosote build up faster?

Cool smoke that lingers. The EPA says the longer smoke stays in the flue, the more likely creosote is to form, and names the conditions that bring that about:

• Too little air. Closed appliance doors, a damper that is not open wide enough, or too little air flow to move smoke quickly up the chimney.
• Unseasoned wood. A lot of energy goes into driving water out of the logs first, which makes more smoke.
• A cold chimney. In very cold weather condensation happens more readily.
• An overloaded stove. Packing the firebox for a longer burn.

The University of Missouri Extension names three causes, wet wood, incomplete combustion and cool surfaces, and gives a number: keep the flue temperature above 250 degrees Fahrenheit to prevent creosote from condensing. A stovepipe thermometer shows whether you are there.

Newer stoves cut both ways. The EPA says certified wood stoves burn more efficiently than older ones and so leave less creosote. The Missouri extension service points out that an efficient stove also sends less heat up the chimney, which cools the flue, and advises extra inspections to make sure deposits are not building.

What happens during a chimney fire?

The deposit itself catches. The Missouri extension service says this is most likely during a very hot fire in the stove, and describes an intense fire with a roaring noise and flames and sparks shooting from the top of the chimney. CSIA's description adds loud cracking and popping, dense smoke and an intense, hot smell.

Not every chimney fire announces itself. CSIA says the majority go undetected: slow-burning fires that never get enough air or fuel to be visible, yet reach very high temperatures and can do as much damage as the dramatic kind.

The damage comes from heat. CSIA puts the temperature of a fire in a masonry chimney at around 2000 degrees Fahrenheit, which it says can melt mortar, crack tiles, cause liners to collapse and damage the outer masonry. Cracked tiles and displaced mortar then give flames a pathway to the wood frame of the house. Factory-built metal chimneys are tested to withstand flue temperatures up to 2100 degrees, CSIA says, but can still be damaged, and a damaged one must be replaced, not reused.

What should you do while it is burning?

1. Call the fire department immediately. Both the extension service and CSIA say so, and CSIA's wording is to call 911.
2. If it is a stove, close all its openings and draft controls.
3. If the fire in the stove or firebox is burning vigorously, use a multipurpose dry chemical extinguisher on it, or throw baking soda onto it. The extension service says the chemical travels up the flue and may put the chimney fire out.
4. Do not pour water in. The extension service warns that the quick cooling can crack a tile liner or warp a metal chimney.

What has to happen before you light another fire?

An evaluation, even if the fire seemed to burn itself out. CSIA advises not using the chimney until it has been swept and examined by a qualified professional, because the flue may have suffered joint failure, metal fatigue or structural cracking that cannot be seen from above or below.

Do not treat the fire department's visit as that evaluation. CSIA says the department's job is to contain, control and suppress the fire, and that inspecting the chimney is outside its training.

In CSIA's account the chimney is swept first, so that every surface is exposed, and then a camera is run through the flue to check each tile and joint. Two practical points from the same source:

• Ask the sweep to photograph the damage and the creosote before the chimney is swept, and to put any repair estimate in writing. CSIA says most chimney fire damage is treated as a covered loss under homeowners insurance. That is the trade body's statement, so confirm it with your own insurer.
• Expect the repair to match the damage. CSIA says it may be a few flue tiles, a new liner or, at worst, a rebuilt chimney.

Skipping the repair is the real risk. The Missouri extension service says that if cracks or holes in the flue are left, sparks from ordinary use could pass through them into the attic or the framing around the chimney.

How do you keep creosote from reaching that point?

• Burn only dry, seasoned wood. The EPA says to season it for at least six months and that it burns best below 20 percent moisture.
• Build hot fires and avoid smoldering ones.
• Have the flue inspected every year. CSIA's threshold for sweeping a masonry fireplace is 1/8 inch of sooty buildup, and sooner if any glaze is present.

How often a chimney should be swept covers the interval for heavy and light users, and signs your chimney needs attention lists the traces a past chimney fire leaves. Powders and sweeping logs are dealt with in doing it yourself or hiring. Local businesses are on the chimney sweeps directory page.

Sources

1. Frequent Questions about Wood-Burning Appliances, U.S. Environmental Protection Agency
2. Best Wood-Burning Practices, U.S. Environmental Protection Agency
3. Preventing Chimney Fires, Chimney Safety Institute of America (CSIA)
4. What You Need to Know After a Chimney Fire, Chimney Safety Institute of America (CSIA)
5. Homeowner Resources, Chimney Safety Institute of America (CSIA)
6. Cleaning Stovepipes and Chimneys, University of Missouri Extension
7. Wood Stove Maintenance and Operation, University of Missouri Extension
8. Heating Fires in Residential Buildings (2017-2019), U.S. Fire Administration
9. Safety with heating equipment, National Fire Protection Association (NFPA)