Chimney fires
Creosote and chimney fires
Creosote is the combustible residue left when wood smoke cools on the way up a flue. CSIA describes it as black or brown, and as crusty and flaky, tar-like and sticky, or shiny and hardened — often all in one system. If enough of it is present and flue temperatures are high enough, it can ignite. That event is a chimney fire.
This page restates public consumer material from CSIA, NFPA, and the U.S. Fire Administration. It is not an inspection of your chimney and not legal or code advice.
What the numbers actually say
Heating equipment is a leading cause of home fire deaths. NFPA reports that fire departments responded to an estimated average of 37,365 heating-equipment fires per year in 2020–2024 (11% of reported home fires), with estimated annual losses of 417 civilian deaths, 1,260 civilian injuries, and $1.2 billion in property damage.
In those same averages, the larger (non-confined) fires involving fireplaces or chimneys were fewer than one in ten heating-equipment fires (6%) but caused nearly one-fifth of the direct property damage (19%). Nearly half of heating equipment fires (46%) occurred from December through February.
USFA, using 2021 figures, still lists heating as the second leading cause of home fires (an estimated 32,200 home heating fires that year) and tells the public to have heating equipment and chimneys cleaned and inspected each year by a professional.
Those figures cover all heating equipment, not only wood chimneys. Space heaters account for a large share of deaths. Fireplace and chimney fires are a smaller share of incidents and a larger share of property damage among heating fires. The practical response NFPA and USFA publish is still annual inspection and cleaning before the season, plus 3-foot clearance from anything that can burn.
Sources: NFPA Home Heating Safety (NFPA Research Division, 2020–2024 averages); USFA Heating Fire Safety.
How creosote builds
CSIA lists restricted air supply, unseasoned wood, and cooler-than-normal chimney temperatures as conditions that accelerate creosote on flue walls. Closing glass doors, not opening the damper fully, starving a wood stove of air too soon, overloading a stove for a long burn, and burning wet wood all keep smoke in the flue longer or cooler.
CSIA’s cleaning threshold, again: masonry systems at 1/8 inch of sooty buildup, and sooner if glaze is present; factory-built systems when any appreciable buildup occurs.
Sources: CSIA Preventing Chimney Fires; CSIA Homeowner Resources.
What a chimney fire can look like — and what it may not
CSIA describes dramatic chimney fires as loud cracking or popping, dense smoke, an intense hot smell, flames or smoke from the top of the chimney, or a rumble that people compare to a freight train. CSIA also states that the majority of chimney fires go undetected: slow-burning fires may not be obvious and are found later on inspection, but temperatures can still damage the chimney and nearby combustibles.
If a chimney fire is in progress, the fire department is the right call. CSIA notes that masonry chimney-fire temperatures can crack tiles, displace mortar, and open a path to the wood frame. Factory-built metal chimneys damaged by a chimney fire, CSIA says, should no longer be used and must be replaced.
That is CSIA’s published consumer guidance. A local fire official decides what is safe to occupy and when a system may be used again.
Nine signs CSIA says a sweep looks for
From CSIA Preventing Chimney Fires:
- “Puffy” or honeycombed creosote
- Warped metal of the damper, smoke-chamber connector, or factory-built chimney
- Cracked or collapsed flue tiles, or tiles with large chunks missing
- Discolored or distorted rain cap
- Heat-damaged TV antenna on the chimney
- Creosote flakes on the roof or ground
- Roofing damaged from hot creosote
- Cracks in exterior masonry
- Evidence of smoke escaping through mortar joints of masonry or tile liners
CSIA’s advice if you think a chimney fire has occurred: have a CSIA Certified Chimney Sweep evaluate the system before you use it again. NFPA 211’s inspection-level framework treats a chimney fire as an event that moves the work beyond a routine Level 1 look. Confirm the level with the technician. Verify the credential on CSIA’s finder.
Carbon monoxide is a separate, related reason to inspect
A blocked or deteriorated flue can put combustion gases, including carbon monoxide, into the living space. CSIA, CPSC, NFPA, and others recommend annual heating-system and chimney maintenance for that reason as well as fire. Working CO alarms are part of ordinary home fire-safety practice; they do not replace an inspection.