How often should a chimney be inspected and cleaned?

Short answer

Have the chimney inspected once a year, and swept whenever the inspection finds creosote. If you burn more than a cord of wood a season, have it swept mid-season too. A gas fireplace needs the yearly inspection as much as a wood one, though it rarely needs sweeping. The inspection and sweep together take a chimney professional 60 to 90 minutes and cost $150 to $350, and fall, before the first fire, is the time to book it.

Why it matters

Wood smoke carries unburned tar, and as it cools in the flue the tar condenses on the walls as creosote. Creosote is fuel. A thin, sooty layer is normal. A thick, glazed layer is a chimney fire waiting for a hot enough blaze below it, and a chimney fire burns at a temperature that cracks flue liners and can set the roof framing alight. Many chimney fires go unnoticed, which is how the liner gets damaged for the next one.

The inspection covers more than creosote. The flue liner cracks with age and with every chimney fire. The damper rusts and sticks. The cap at the top lets in rain and animals when it's damaged. A gas fireplace has its own hazards: a blocked or disconnected vent sends carbon monoxide into the house instead of up the chimney, and the only way to know the vent is sound is to look. A yearly inspection catches all of it, and sweeping removes the one thing that can turn a fireplace into a house fire.

When to do it more often

Burning more than a cord of wood a season: a mid-season sweep on top of the yearly one. Heavy use builds creosote faster than once-a-year sweeping removes it.
Burning wet or unseasoned wood: the same, since wet wood smolders and makes far more creosote than dry wood.
A gas fireplace: a yearly inspection, which it rarely needs more often than, but the vent and the burner should be looked at before every heating season.
After a chimney fire, or a suspected one: inspect before the next fire, whatever the schedule says.

What you need

Nothing for the professional visit. A flashlight is enough for your own look between visits: shine it up the flue from the firebox with the damper open, and look for flakes on the walls and daylight at the top.

Steps at a glance

Book the sweep in late summer or early fall, before the rush.
Stop using the fireplace a day or so before the visit, so the firebox is cold.
The sweep inspects the firebox, damper, smoke chamber and flue, often with a camera, and checks the cap and crown from the roof.
They sweep the flue with brushes and a vacuum that keeps the soot out of the room.
They tell you what they found: the creosote level, the liner's condition, and anything that needs repair.
For a gas fireplace, they check the vent connections, the burner and the pilot, and clean the glass.

You're done when the flue is clean, the damper moves freely, and the sweep has signed off the liner and the cap.

Signs it's overdue

Flakes of creosote in the firebox, or a crust on the flue walls when you look up with a flashlight.
Smoke coming into the room when the fire is lit.
A soot smell in the room when the fireplace is cold, especially in humid weather.
A damper that's stiff or won't open fully.
Cracked bricks or mortar in the firebox.
Animal noises in the chimney, which mean the cap is missing or damaged.

DIY or pro

This is a pro-recommended job, and the reasons are the roof and the judgment. A sweep works from the top of the chimney as well as the bottom, and knows what a cracked liner or a dangerous level of creosote looks like. Brush kits are sold for homeowners, and a flue in good condition that's swept regularly can be done that way, but the inspection is what catches the problems a brush doesn't.

A certified chimney sweep charges $150 to $350 for an inspection and sweep. If the inspection turns up a cracked liner or a failing crown, the repair is a separate quote, and it's one to take seriously, since a damaged liner means no fires until it's fixed.

Safety

Gas: a gas fireplace vents carbon monoxide through its chimney or vent, and a blocked or separated vent sends it into the house. Have the vent inspected yearly, keep a carbon monoxide alarm on the same floor, and if you smell gas at the fireplace, shut off its valve and call the gas company.
Structural: a cracked flue liner or a damaged chimney crown lets heat and embers reach the framing. Don't use a fireplace that a sweep has flagged until it's repaired, and don't climb the roof to look at the chimney yourself.

FAQ

How often does a chimney need to be cleaned?

Inspected once a year, and swept when the inspection finds creosote. Heavy use, more than a cord of wood a season, means a mid-season sweep as well.

Does a gas fireplace need to be inspected?

Yes, once a year. The vent, the burner and the pilot are checked, and a blocked vent is a carbon monoxide risk.

How do I know if my chimney has creosote?

Shine a flashlight up the flue from the firebox. Flakes or a crust on the walls, or flakes falling into the firebox, mean creosote is building.

What happens if you don't clean your chimney?

Creosote builds until a hot fire ignites it. A chimney fire cracks the liner and can spread to the house.