Creosote: What It Is, Why It's Dangerous, and How to Prevent It
By Chimney Cleaners Editorial · January 8, 2026 · 5 min read
Creosote is the tar-like fuel that causes 25,000+ chimney fires every year in the US. Here's how it forms and how to keep it out of your flue.
Creosote is what happens when wood smoke condenses on a cool flue wall. It starts as a light, sooty powder (Stage 1), thickens into flakes (Stage 2), and eventually hardens into a shiny black glaze (Stage 3) that ignites at just 451°F.
The three stages
- Stage 1: Loose, powdery soot—removed with a standard sweep.
- Stage 2: Puffy, flake-like deposits—requires rotary tools.
- Stage 3: Glazed, tar-like coating—requires chemical treatment (PCR) plus rotary extraction.
How to prevent it
- Burn only seasoned wood (moisture below 20%)
- Never burn softwoods or construction scrap in a fireplace
- Let the fire breathe—starving it produces more smoke
- Insulate exterior flues to keep them warm
- Sweep annually