Every time you burn wood, your chimney collects creosote — a dark, tar-like residue that’s the leading cause of chimney fires. Here’s what it is, why it’s so dangerous, and how it’s properly removed.
What is creosote?
Creosote forms when the smoke, water vapor, and gases from burning wood cool and condense on the inside of the flue. Over time it hardens into a flammable coating. The cooler your flue runs and the wetter your wood, the faster creosote builds up.
The three stages of creosote
- Stage 1: a light, flaky soot that’s easy to brush away during a routine sweep.
- Stage 2: harder, shiny black flakes that are more stubborn to remove.
- Stage 3: a thick, tar-like glaze that’s highly flammable and very difficult to remove — the most dangerous stage.
Why creosote is dangerous
Creosote is essentially fuel lining the inside of your chimney. When it ignites — often from a stray spark or an over-hot fire — it can cause a chimney fire that reaches over 2,000°F, cracking the liner and spreading to the home. Heavy buildup also restricts airflow, which can push smoke and carbon monoxide back into the house.
How creosote is removed
Stage 1 and 2 creosote is removed by a professional sweep using specialized brushes and rods. Stage 3 glaze may require rotary tools or chemical treatments — and in severe cases, a damaged liner may need to be resurfaced. “Creosote sweeping logs” you buy at the store can loosen some light buildup, but they are not a substitute for a professional cleaning.
How to prevent creosote buildup
- Burn only dry, seasoned hardwood (under 20% moisture)
- Keep fires hot rather than smoldering — low, slow fires create the most creosote
- Make sure your flue is properly sized and drafting well
- Get an annual cleaning and inspection
Worried about creosote?
A professional sweep removes creosote before it becomes a fire hazard.