Signs your chimney needs sweeping, inspection or repair

Updated November 10, 2026 · KeystoneProGuide editorial team

What are the signs that a chimney needs attention?

Smoke in the room, a smell from the fireplace, soot you can scrape off the flue wall, bits of tile or mortar in the firebox, stains on the outside of the stack and any trace of animals. Each one is a reason to book an inspection before the next fire. So is a calendar: if more than a year has passed since the chimney was last looked at, that alone is enough.

The sections below take the signs by where you meet them.

What should you notice at the fireplace or stove?

Smoke where it should not be. The Environmental Protection Agency says a properly installed, correctly used wood-burning appliance should generate very little smoke, and that regularly seeing or smelling smoke may mean a problem. Its advice if you smell smoke in the house is to have the appliance checked by a certified chimney sweep or similar professional.

The University of Missouri Extension lists the usual causes of a smoky fire:

• an obstruction in the flue, such as a bird nest or fallen bricks;
• too little combustion air in a tightly built or recently remodeled house, which opening a window slightly usually cures;
• unusual wind;
• green or wet wood, or a fire too cool to warm the chimney and get it drawing.

The first of those is a job for a sweep. The others are worth ruling out yourself.

A smell, especially in summer. CSIA, the trade's certification body, says the odor comes from creosote deposits and is usually worse when the humidity is high and the air conditioner is running. It says a sweeping will help but usually will not cure it, because the underlying cause is air being drawn down the chimney.

Visible buildup. CSIA recommends sweeping a masonry fireplace at 1/8 inch of sooty buildup, and sooner if there is any glaze. Creosote, in its description, can be crusty and flaky, tar-like and sticky, or shiny and hardened.

A weak fire. HomeGuide's list of signs includes a fire that burns weakly or is hard to start, and excessive smoke entering the room when you light it.

Debris in the firebox. HomeGuide lists masonry or creosote debris falling into the firebox. In a flue that serves a gas appliance, CSIA says clay liner tiles can flake off under corrosive conditions and block the chimney.

Animals. Signs of birds, animals or nests are on HomeGuide's list as well, and CSIA names animal and bird nests among the things that obstruct flues.

What can you see from outside?

This Old House lists the common outward signs of chimney damage:

• cracked or crumbling mortar joints;
• white staining on the bricks, called efflorescence;
• a rusted or missing chimney cap;
• water leaks near the chimney or fireplace.

Dark stains matter too. The Consumer Product Safety Commission said in a 1997 release that creosote buildup or leakage could cause black stains on the outside of the chimney or flue, and that such stains can mean pollutants are leaking into the house. On the metal pipe between a furnace and its chimney, an earlier release from the same agency told inspectors to look for rust or cracks.

How does a past chimney fire show itself?

Often it does not, which is the point. CSIA says the majority of chimney fires go undetected, because slow-burning ones lack the air or fuel to be dramatic, yet they reach very high temperatures. A loud one is hard to miss: CSIA describes cracking and popping, dense smoke and an intense hot smell, and the Missouri extension service describes a roaring noise with flames and sparks from the chimney top.

The traces a sweep looks for afterwards, from CSIA's list of nine, include:

• creosote that has turned puffy or honeycombed;
• warped metal in the damper or the connector pipe;
• flue tiles that are cracked, collapsed or missing chunks;
• a discolored or distorted rain cap;
• flakes of creosote on the roof or the ground;
• smoke escaping through mortar joints.

If you think there has been a fire in the flue, CSIA's advice is not to use the chimney again until it has been swept and evaluated, because the damage often cannot be seen from above or below.

Which signs point to carbon monoxide instead of soot?

None that your senses can pick up. The EPA says carbon monoxide is impossible to see, taste or smell. What you may notice is how people feel. The Centers for Disease Control and Prevention lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion. The EPA adds a telling detail: flu-like symptoms that clear up after leaving home.

Its list of sources includes leaking chimneys and a flue that is blocked, disconnected or the wrong size. If a carbon monoxide alarm sounds, the Consumer Product Safety Commission says not to look for the cause: move outside to fresh air and call the fire department or 911.

Does no sign mean no problem?

No. Two of the main hazards give no warning. Most chimney fires pass unnoticed, in CSIA's account, and carbon monoxide cannot be sensed at all. That is the reason the fire and health agencies recommend a yearly inspection whether or not anything seems wrong, and how often a chimney should be swept sets out what each of them says.

The opposite caution applies when the sign comes from a stranger. A piece of brick or a photograph shown to you on the doorstep is not evidence about your chimney. Chimney sweep scams to avoid explains why. Businesses that can inspect yours are on the chimney sweeps directory page.

Sources

1. Best Wood-Burning Practices, U.S. Environmental Protection Agency
2. Frequent Questions about Wood-Burning Appliances, U.S. Environmental Protection Agency
3. Carbon Monoxide's Impact on Indoor Air Quality, U.S. Environmental Protection Agency
4. Chimneys for Wood Stoves, University of Missouri Extension
5. Wood Stove Maintenance and Operation, University of Missouri Extension
6. Homeowner Resources, Chimney Safety Institute of America (CSIA)
7. Preventing Chimney Fires, Chimney Safety Institute of America (CSIA)
8. What You Need to Know After a Chimney Fire, Chimney Safety Institute of America (CSIA)
9. Avoiding Carbon Monoxide Hazards, Chimney Safety Institute of America (CSIA)
10. How much does a chimney sweep cost?, HomeGuide
11. How Much Does Chimney Repair Cost?, This Old House
12. CPSC Urges Annual Fuel-Burning Appliance Inspection to Prevent Deaths, Fires, U.S. Consumer Product Safety Commission
13. Inspect Home Furnace System For Hazards, Carbon Monoxide, U.S. Consumer Product Safety Commission
14. Carbon Monoxide Questions and Answers, U.S. Consumer Product Safety Commission
15. Carbon Monoxide (CO) Poisoning Basics, Centers for Disease Control and Prevention