Guide — Solid Fuel & Open Fires
Chimney Fire Prevention
A chimney fire burns at over 1,000 °C — hot enough to crack flue linings and ignite roof timbers in minutes. Almost every chimney fire is preventable with the right sweeping schedule and fuel choice.
Key rule
Creosote is the cause of nearly all chimney fires. It builds up from burning wet wood, smouldering fires, or infrequent sweeping. The only reliable prevention is burning dry, seasoned wood (below 20 % moisture) and sweeping to the recommended schedule for your fuel.
Recommended sweeping frequency by fuel type
Guidance from HETAS, NACS, and the Solid Fuel Association — endorsed by UK fire and rescue services.
| Fuel type | Sweeping frequency |
|---|---|
| Smokeless coal | Once a year |
| Bituminous (house) coal | Twice a year |
| Wood (seasoned, <20 % moisture) | Twice a year minimum |
| Wood (unseasoned / wet) | Quarterly — if burning at all |
| Oil-fired appliance | Once a year |
| Gas fire with open flue | Once a year |
Warning signs of a chimney problem
Active chimney fire — call 999 immediately
Blockage or flue failure — extinguish fire, call 999
Creosote ignition — evacuate, call 999
Structural chimney damage — do not use, call engineer
Creosote leaching — flue lining failed, inspect before use
Blocked flue or downdraught — sweep before next use
What causes chimney fires?
The primary cause is creosote — a tar-like residue that condenses on the inside of the flue as wood gases cool. Creosote builds up fastest when burning wet or unseasoned wood, running fires at low temperatures (smouldering), or using an oversized stove with the air vents closed down. Once ignited, creosote burns intensely and is almost impossible to extinguish from inside the property.
A flashover in the room adjacent to a chimney breast is a real risk if the flue lining fails during a chimney fire — the heat can ignite wall cavities and roof spaces before occupants are aware.
Choosing and seasoning wood
Moisture content is the single most controllable variable. Wood above 20 % moisture produces significantly more creosote than dried wood. Key rules:
- Buy logs from a Woodsure Ready to Burn certified supplier
- Store logs in a ventilated, covered woodstore for at least 12–18 months if self-cutting
- Test moisture with a wood moisture meter before burning (<20 % target)
- Never burn treated, painted, or composite wood — toxic fumes and rapid creosote build-up
- Avoid burning household waste, cardboard, or paper as primary fuel
What to do if you have a chimney fire
- Call 999 immediately. Do not wait to see if it burns out.
- Close all stove doors, air vents, and fireplace dampers to starve oxygen.
- Evacuate everyone — including pets — and close doors behind you.
- Do not attempt to extinguish with water — thermal shock can shatter clay flue liners.
- Do not re-enter until fire service confirms the building is safe.
After any chimney fire, have the flue inspected by a HETAS engineer before relighting. A cracked liner must be relined before the chimney is used again. See our guidance on get out, stay out for the general evacuation principle that applies here.
Annual maintenance checklist
- Book a HETAS or NACS-registered sweep before the start of each heating season
- Fit a cowl or bird guard to keep debris and nesting material out of the flue
- Check the chimney pot and pot mortar for cracks after winter
- Ensure the CO alarm in the room is within its rated service life
- Keep the sweep certificate — required by most insurers
For a broader look at heating risks in the home, see our home fire risk assessment guide and the heating season checklist.
Frequently asked questions
FAQ