How often should you have your chimney swept?

Why bother

Creosote buildup is a flue fire waiting to happen. This is an essentials-tier job. Skip it and you're inviting the expensive kind of problem, or the dangerous kind.

Why it's a range

Wood and coal cake the flue with creosote fast and want a yearly sweep; a gas log is mostly a quick inspection. Burn a lot of wood and once a year is the floor, not the ceiling.

What the job involves

1. Book a certified sweep for a once-a-year look. They lay drop cloths so the soot stays in the firebox and not on the carpet, then run a NFPA 211 Level 1 inspection of the flue, inside and out, the bits anyone can reach.
2. Let them do the dirty part. Brushes and rods go up the flue to scrub the creosote and soot off the liner walls, then the firebox and the smoke shelf get vacuumed out.
3. Have them check the cap, damper, crown and liner for cracks, blockages like birds' nests and debris, and any glazed creosote that brushing won't budge.
4. Read the report. They'll tell you the creosote level and flag any repairs. The rule is sweep at 1/8 inch of buildup, or sooner if there's glaze, so a heavy wood burner may need it more than once a season.

Do it yourself, or pay someone?

Mostly a pro. You can buy a brush-and-rod kit, but the sweep also catches liner cracks, blockages and glazed creosote you'd miss, so it's worth the money. A sweep and inspection runs about $129 to $381, averaging roughly $254; gas fireplaces are cheaper at $80 to $150, and a badly neglected chimney can reach $800.

What skipping it costs

$900 to $7,000 to replace the flue liner after a chimney fire, and that's the tidy end. Creosote builds up inside an unswept flue, and it only takes about 1/8 inch of the stuff to be a fire hazard. A buildup of creosote is one of the leading causes of chimney fires, and a chimney fire cracks or breaches the liner. A partial-to-full rebuild after serious damage runs higher, $1,500 to over $20,000, and a fire that spreads into the house stops being about the chimney at all. A yearly sweep is the cheap end of all of that.

Signs it's overdue

• A strong acrid smell like burning tar or asphalt near the fireplace, or smoke drifting back into the room instead of going up the flue. That's the draft giving up.
• Black, shiny, tar-like deposits, or a soot and creosote layer 1/8 inch thick or more inside the chimney. That thickness on its own means it's time to sweep.
• Flakes or debris dropping into the firebox, dark stains around the fireplace opening, or a fire that won't stay lit.

When to start thinking about it

This usually means booking someone, so the grumbling starts 30 days ahead to leave time to line it up. Mark it done and Grumpty sets the next one, every 12 months, so you can go back to forgetting it exists.

Questions people ask