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Chimney · Safety

Creosote build-up in a wood-burning flue

Creosote is what chimney fires burn. Annual inspection and sweeping for a regularly used wood appliance is not optional maintenance.

Quick answerCreosote is the tar-like residue that smoke leaves on the inside of a flue as it cools. It’s flammable, and it’s what chimney fires burn. Every wood fire adds some. For a regularly used wood stove or fireplace, annual inspection and sweeping is not optional maintenance. NFPA 211 recommends an inspection once a year, with sweeping when the inspection shows it’s needed.

A chimney fire can crack flue tiles and damage the chimney even if nobody notices it at the time. Keeping creosote down is cheaper than finding out what one did.

Firewood burning in a fireplace
Firewood burning in a fireplace. Every wood fire leaves some creosote in the flue above it. Photo by Hayden Scott on Unsplash.

1Why creosote builds up

  • Wet wood. Unseasoned wood burns cool and smoky, and more of that smoke condenses in the flue.
  • Smoldering fires. Damping a fire down to burn slowly overnight makes more creosote.
  • Cold flues. Exterior chimneys and oversized flues stay cooler, so smoke condenses faster.
  • Restricted air. A closed-down air supply or a partly blocked flue slows the smoke and lets it deposit.

2Signs to watch for

  1. Look at the damper areaWith the fire out and cold, use a flashlight. Black, flaky, crusty or shiny tar-like deposits are creosote.
  2. Notice the smellA strong, smoky or tar smell from the fireplace, especially in humid weather, can mean heavy build-up.
  3. Watch the draftSmoke rolling into the room or fires that struggle to draw can mean a restricted flue.
  4. Know the signs of a chimney fireLoud cracking or popping, a roaring sound, dense smoke or a strong hot smell. If you suspect one, get out and call 911.
Chimney fire

If you think the chimney is on fire, get everyone out of the house and call 911 or the fire department from outside. Don’t use the fireplace again until it has been inspected.

3Keeping it under control

What you can do

  • Burn only dry, seasoned wood
  • Burn hotter, shorter fires rather than slow smoldering ones
  • Never burn trash, cardboard or treated wood
  • Keep working smoke and CO alarms

Hire a pro

  • The annual inspection
  • Sweeping the flue when needed
  • Removing heavy, glazed creosote
  • Checking for damage after a suspected chimney fire

Heavy, glazed creosote is hard to remove and may need special tools or treatments. That’s a job for a chimney sweep, not a store-bought brush.

4What drives the cost

A routine sweep and inspection is the low end. Costs rise with heavy or glazed creosote, a hard-to-reach roof, multiple flues, and any damage found afterward, such as cracked flue tiles that need relining.

Chimney cost

Due for a sweep?

Talk to a chimney pro about an annual inspection and sweeping for your wood-burning appliance.

877-360-4657

5Questions

How often should I have the chimney swept?

Have it inspected once a year, as NFPA 211 recommends, and swept when the inspection shows build-up. Heavy users may need it more often.

Do creosote-removal logs work?

They may help loosen some deposits, but they aren’t a substitute for an inspection and sweep.

Does a gas fireplace make creosote?

Not the way wood does. Gas appliances still need their venting checked; see the gas venting guide below.

Written by Jaylan Jones. I Like To Exterior Services earns a referral fee when a call connects to a contractor. See our business-model disclosure.

877-360-4657