Chimney Fires: Signs, Causes and Prevention

Is this a chimney fire?

A chimney fire can burn explosively, loud enough for neighbors or people passing by to notice. Flames or dense smoke may shoot from the top of the chimney, and people describe a low rumbling sound like a freight train or a low-flying airplane. CSIA (source, opens in a new tab) Check what you are seeing and hearing:

Most chimney fires are never noticed

The Chimney Safety Institute of America says the majority of chimney fires go undetected: slow-burning fires that do not get enough air or fuel to be visible, but still reach very high temperatures and can do as much damage to the chimney and nearby parts of the house. CSIA (source, opens in a new tab)

Signs a sweep looks for after a chimney fire include puffy or honeycombed creosote, warped metal on the damper or connector pipe, cracked or collapsed flue tiles, a discolored or distorted rain cap, creosote flakes on the roof or the ground, and smoke escaping through mortar joints. CSIA (source, opens in a new tab)

Creosote: what builds up and why

When wood burns, the smoke carries water vapor, gases, unburned wood particles and tar fog up the chimney. As it cools, a residue condenses on the inside of the flue: creosote. It can be black or brown, crusty and flaky, tar-like and sticky, or shiny and hard, and all of it is highly combustible. CSIA (source, opens in a new tab)

Three things speed up creosote buildup: a restricted air supply, unseasoned wood, and a chimney that runs cooler than normal. CSIA (source, opens in a new tab) In practice that means:

• Burn seasoned wood. Wet wood wastes its heat driving off water, so the smoke stays cooler and leaves more creosote. CSIA (source, opens in a new tab)
• Give the fire air. Open the damper wide enough, and do not close a wood stove's air controls down too soon or too far. CSIA (source, opens in a new tab)
• Do not overload the firebox of a wood stove to get a longer burn. CSIA (source, opens in a new tab)

How often should a chimney be cleaned?

Have it inspected every year, and swept or repaired whenever the inspection says it is needed. CSIA (source, opens in a new tab) NFPA and the U.S. Fire Administration give the same advice for all heating equipment: cleaned and inspected each year by a qualified professional. NFPA (source, opens in a new tab) USFA (source, opens in a new tab) An annual inspection also helps keep carbon monoxide out of the house. CSIA (source, opens in a new tab)

Fireplaces and chimneys are involved in a small share of heating fires, about 6%, but those fires cause nearly one-fifth (19%) of the property damage from heating fires. NFPA (source, opens in a new tab)

Wood stove and fireplace safety

• Install a wood stove according to the manufacturer's instructions, or have a professional do it. NFPA (source, opens in a new tab)
• Vent all fuel-burning equipment to the outside, and keep working CO alarms in the home. NFPA (source, opens in a new tab)
• Use a sturdy fireplace screen to stop sparks flying into the room. NFPA (source, opens in a new tab)
• Keep anything that can burn at least 3 feet from the fireplace or stove, and keep a 3-foot kid-free zone around open fires. NFPA (source, opens in a new tab)

Disposing of ashes

Let ashes cool before you put them in a metal container, and keep that container a safe distance from your home. NFPA (source, opens in a new tab)

After a chimney fire

Do not use the chimney again until a qualified chimney professional has swept and evaluated it: the fire may have cracked the structure in places you cannot see from above or below. CSIA (source, opens in a new tab) A damaged factory-built metal chimney should not be used again and must be replaced. CSIA (source, opens in a new tab) The fire department's job on the night is to contain and put out the fire; evaluating the chimney afterwards is a sweep's job. CSIA (source, opens in a new tab)

Call your insurer. The Chimney Safety Institute of America says most chimney fire damage is considered a covered loss under homeowners' insurance, and suggests asking your sweep to photograph the damage and the creosote before sweeping, and to put any repair estimate in writing for the adjuster. CSIA (source, opens in a new tab)

Frequently asked questions