Noises in the Chimney and What They Mean

The one sound that cannot wait

CSIA describes the sounds people report during a chimney fire as a loud cracking and popping noise, or a low rumbling that reminds them of a freight train or a low-flying airplane. Dense smoke, flames or sparks from the chimney top and an intense, hot smell often come with it.

Everything else on this page is less urgent, and the way to sort it out is to notice when the sound happens. The sections below follow that idea: what the house, the weather and the appliances were doing at the moment you heard it.

A short listening log

Noises are hard to describe after the fact. For a few days, jot down each time you hear it:

• The time of day, and whether it was dawn, dusk or the middle of the night.
• The weather: wind, rain, a sudden temperature drop.
• What was running: a fire, a stove, a gas fireplace, the furnace or boiler, the water heater.
• Where it seemed to come from: the firebox, behind a wall, the attic, the roof.
• What it sounded like, in your own words. A phone recording helps even more.

Resist opening the damper for a look if an animal might be up there. A startled raccoon or bird may drop straight into the firebox and the room. The log, and a recording, will be more useful to whoever checks the chimney than a look up the flue.

While an appliance heats up or cools down

Steel and cast iron grow as they warm and shrink as they cool, and the movement is often audible. Heat & Glo's owner's manual for one of its gas fireplaces lists a metallic noise as a normal question and explains it as metal expanding and contracting as it heats up and cools down, comparing it to the sound of a furnace or heating duct. Wood stoves, inserts, stovepipe and factory-built metal chimneys make similar ticks, pings and the occasional soft bang.

Those sounds are generally harmless when they:

• happen only during warm-up and cool-down,
• have been there since the appliance was new, and
• come with no smoke, odor or soot.

Pay closer attention when a loud new bang appears, when a sound comes with a smell of smoke or gas, or when a connector pipe seems to move. The Consumer Product Safety Commission lists loose or disconnected vent and chimney connections among the signs that an appliance may not be venting properly. Turn the appliance off if you can do so safely and have it checked. A gas smell is a different matter entirely: get out first, then phone the gas company or 911 once you are away from the building.

When the wind picks up

Wind moving across the open top of a flue can make it hum, whistle or moan, much like blowing across a bottle. That alone is not a defect, though it can be louder with some cap styles or on an uncapped flue.

Rattling, clanking or rhythmic banging in wind is different. It usually means something at the top of the chimney is loose:

• A cap whose fasteners have worked free or rusted, or one that has shifted on the flue tile.
• The lid of a top-sealing damper that is not seating, or whose cable has slack.
• A metal chase cover or storm collar on a factory-built chimney.
• Antenna straps, satellite brackets or old flashing pieces attached to the stack.

Look from the ground with binoculars after a windy night and compare the cap with an older photo. A cap that has tilted or lifted can blow off in the next storm. See chimney cap types compared and our guide to checking the chimney after a storm. Wind gusts can also push air down a flue, which is why some fireplaces puff smoke on windy days.

When it rains

A tapping or pinging inside the fireplace during rain often means water is falling down the flue and landing on the damper or the smoke shelf. That points to an uncapped flue, a damaged cap, or a crack at the top of the flue. A trickling sound behind a wall or ceiling near the chimney is more serious, because the water is already inside the structure.

Some dripping is not rain at all. A gas or oil appliance venting into a flue that is too large or too cold can produce condensation, and in cold weather that water may drip at the base of the flue or around the cleanout door. DuraVent lists leaks around cleanout doors and water stains near the chimney among the signs of that problem. See why chimneys leak and stains on walls and ceilings near the chimney.

When nothing is running at all

Sounds in an idle chimney, especially scratching, scrabbling, chirping or fluttering, usually come from animals. Timing helps identify them:

• A chattering chorus in late spring and summer, rising when an adult bird flies in. The U.S. Fish and Wildlife Service describes the chimney swift's exuberant chittering as easy to recognize, notes that swifts arrive in March or April and leave in August or September, and says food-begging calls come from the young in the weeks before they leave. Swifts and their nests are protected under the Migratory Bird Treaty Act, so an active nest is left alone until the birds go.
• Chirping from the fireplace in spring, with heavier thumps. The Internet Center for Wildlife Damage Management notes that chirping in spring often means a raccoon raising young above the damper.
• Frantic scratching or fluttering that does not stop. The same source explains that most animals that fall into a flue, such as squirrels, starlings and pigeons, cannot climb back out. A trapped animal will not leave on its own.

Keep the damper closed, never use smoke or fire to force an animal out, and do not cap the chimney until you know it is empty. See animals and nests in the chimney.

Rattles, thuds and something landing

A sudden rattle down the flue followed by a small thud often means something fell. Check a cold firebox, the smoke shelf if you can see it with a flashlight, and the cleanout at the base of the flue, and take a photo of what you find:

• Flakes of soot or creosote. Falling soot or debris is on the CPSC's short list of warning signs that combustion gases may not be venting as they should.
• Pieces of clay tile. These can come from a cracked or damaged liner.
• Sand and mortar crumbs. Joints inside the flue may be eroding.
• Twigs, leaves or nest material. Something is, or was, using the chimney.

Any of these is a reason to stop using the fireplace or connected appliance until the flue has been inspected, ideally with a camera.

Sounds tied to the furnace, boiler or water heater

If a noise lines up with the furnace, boiler or water heater cycling on, the flue serving that appliance is part of the question. Gurgling or dripping at the base of the flue, rattling at the vent connector, or a new whooshing or rumbling at burner start-up should be looked at by a qualified heating technician, along with the chimney or vent. Our guides to oil furnace and boiler flues and carbon monoxide and your chimney cover why those flues deserve attention.

The CPSC's carbon monoxide guidance lists headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion as symptoms. If anyone has them, or a CO alarm sounds, get outside to fresh air and call 911.

When we look into a chimney noise, the visit starts with an assessment of the cap, damper and flue, a camera run when the flue allows, and a roof check when it is safe. Your listening log goes a long way. We show you photos of what we found before anything is scheduled. See chimney inspection.

Questions homeowners ask

Sources

1. CSIA: Preventing chimney fires
2. Heat & Glo SL-550METRO owner's manual, installation and operation (PDF)
3. U.S. Fish and Wildlife Service: Chimney swifts
4. Internet Center for Wildlife Damage Management: Chimney caps
5. U.S. Consumer Product Safety Commission: Carbon Monoxide, the invisible killer (Publication 464, PDF)
6. U.S. Consumer Product Safety Commission: Carbon Monoxide Information Center

This guide is general information. It can't diagnose a specific chimney; an inspection can.