How often, in plain numbers
The U.S. Fire Administration says to have chimneys cleaned and inspected each year by a professional. CPSC's chimney safety alert says the same, "more frequently if the chimney receives heavy use," and gives primary heating as the example. For a stove that builds deposits quickly, CPSC says the chimney should be checked as often as twice a month. That alert dates from 1983 and was aimed mainly at metal factory-built chimneys, but the advice on how often to look still holds up.
The Philadelphia Fire Department has said heating equipment is the leading cause of home fires here in December, January and February, according to a City emergency-management winter tip. So book the sweep before December, not after the first cold snap. The same City tip adds one Philly-specific habit worth keeping: never close the damper while there are still hot ashes in the fireplace.
Why it builds up, and how to slow it down
EPA's wood-burning FAQ says creosote forms when smoke rises into a cooler chimney and condenses on the inside walls. It names four things that make it worse:
- Not enough air: a damper that isn't open wide enough, or closed doors that slow the smoke.
- Unseasoned wood: driving the water out of wet logs makes more smoke, and more deposits.
- A cold chimney: very cold outside air makes condensation more likely. An exterior chimney on a brick rowhome or twin gets cold on our winter nights.
- Overloading a wood stove to stretch the burn, which EPA says can also damage the firebox.
The fix is mostly fuel. EPA's burning tips say to season wood for at least six months, store it off the ground with only the top covered, and burn it below 20 percent moisture. EPA says to check with a wood moisture meter, which settles the question better than the seller's word. Don't try to burn deposits off with a very hot fire; CPSC lists too-hot fires as a cause of buckled liners.
What you can tell from the floor
You can't see how much creosote is in a flue from the room, but a few signs point to the conditions that build it. EPA's heating checklist lists a smoldering fire, dirty glass doors and smoke from the chimney top as signs the fire needs more air or the wood isn't dry. Smoke smell in the house is a stop sign: EPA says shut the appliance down, open a window and call a chimney sweep or stove installer. Stay off the roof and don't scrape the flue yourself.
A clogged chimney can also push carbon monoxide into the house, so keep CO alarms working. If one sounds, see when a CO alarm means leave the house.
Who to call and what to ask
Call a certified chimney sweep. EPA's installation and maintenance page points to the Chimney Safety Institute of America (CSIA) and the National Fireplace Institute (NFI) to check credentials. When you book, ask:
- Is this an inspection, a cleaning, or both?
- How much buildup did you find, and should I come back mid-season at the rate I burn?
- Did you check the liner, the crown and the connector pipe, and can I get photos?
- Is any repair you're proposing needed before I light another fire?
If the sweep finds a cracked or missing liner, what a chimney liner does explains the next step. Water damage from above is a separate problem; see why a chimney crown cracks. If you've stopped using the fireplace, what to check before closing one up covers that.
If you think a chimney fire is happening
Get everyone out and call 911 from outside. Don't stay in to confirm it, and don't try to put it out from the firebox. After any chimney fire, real or suspected, CPSC says to have a sweep do a complete safety inspection and make repairs before the chimney is used again. Hot gases can escape through a cracked tile liner and reach framing, so ask specifically whether the liner was checked, not just swept.