How often should you clean your chimney?
Updated July 2026
Have your chimney inspected once a year and swept whenever creosote reaches 1/8 inch — for households that burn wood regularly through the winter, that works out to a sweep about once a year. That's not marketing cadence; it's NFPA 211, the fire-protection standard. Occasional burners (a dozen fires a season) may pass inspection for two or three years between sweeps — but the inspection itself stays annual, because flue damage and blockages don't wait for creosote.
What changes the interval
| Your situation | Interval | Why |
|---|---|---|
| Regular wood burning (weekly fires all winter) | Sweep yearly | A cord or two of wood deposits sweep-worthy creosote in a season |
| Occasional fires (10–15 a year) | Inspect yearly; sweep as measured | The inspector measures creosote — sweep lands every 2–3 years |
| Burning unseasoned ("green") wood | Sweep more than yearly | Wet wood smolders — creosote forms several times faster |
| Wood stove or insert | Sweep yearly | Cooler, slower flue gases condense more creosote than open fireplaces |
| Gas fireplace | Inspect yearly | No creosote, but flues still crack, block, and host nests — CO risk |
| Unused fireplace | Inspect before first use | Animal nests and flue damage accumulate in idle chimneys |
The cost of skipping it
What skipping it costs: creosote is unburned fuel condensed on your flue walls, and at 1/8-inch thick there's enough to sustain a chimney fire — the US logs roughly 20,000+ chimney fires a year causing over $125 million in damage (CSIA). Many burn quietly, cracking flue liners so the next fire reaches the house framing. A sweep is $150–350; a flue reline after a chimney fire is $2,500–7,000; the house is the tail risk.
How to do it (Pro visit · $150–350 · book in late summer, before the fall rush)
- Book a CSIA-certified sweep in late summer or early fall — calendars fill fast once the first cold week hits.
- Ask for a Level 1 inspection with the sweep (visual check of accessible flue, damper, and firebox); Level 2 (camera) after any chimney fire, a home purchase, or a new liner/appliance.
- Between visits, burn only seasoned hardwood (split, dried 6–12 months, moisture under 20%) with hot, active fires — smoldering is the creosote factory.
- Check the chimney cap from the ground: missing caps invite water and nests, the two other chimney killers.
- Keep the damper closed when idle and install a CO alarm on the same floor as the fireplace.
Knowing the interval is the easy half. OnOtto reminds you at the right interval — and won't let you snooze it into next year. Tasks persist until they're done, and completing the annual inspection schedules the next one automatically.
Put this on autopilot — free for 30 daysFrequently asked questions
Do creosote sweeping logs replace a chimney sweep?
No. The logs' additives can dry and flake certain creosote stages, but the flakes still need mechanical removal, tarry glaze doesn't respond, and no log inspects a flue for cracks or blockage. CSIA's position is blunt: they may help between sweeps; they replace nothing.
I only burn a dozen fires a year — do I really need an annual inspection?
Yes, because the inspection isn't only about creosote: it catches flue cracks, failing mortar joints, missing caps, and animal nests — all of which happen to idle chimneys and all of which turn the first cozy fire of December into a CO or house-fire event. Light burners often get 2–3 years between sweeps; the yearly look is what proves it.
Does a gas fireplace or gas-furnace flue need chimney service?
Annual inspection, yes — sweeping, rarely. Gas doesn't make creosote, but its cooler, moist exhaust degrades liners and mortar, and blocked flues (nests, debris, collapsed liner) push carbon monoxide back into the house. The furnace tune-up on the fall checklist plus a flue inspection covers it.
What kind of wood makes the least creosote?
Seasoned hardwood — oak, maple, ash — split and dried 6–12 months to under 20% moisture (a $15 moisture meter removes the guesswork). The burn style matters as much as the species: hot, active fires with adequate air produce a fraction of the creosote of dampered-down overnight smolders, whatever the wood.