By James Rodriguez, Central Chimney Service.
Scratching, fluttering, or a chirping that seems to come from inside the wall is one of the more unsettling sounds a house makes, and in an uncapped chimney it is rarely a mystery. Chimneys are dark vertical shafts with rough walls, which is precisely what several species look for. The part homeowners usually do not know is that the removal has a season, and doing it at the wrong time is both ineffective and, in one specific case, illegal.
Who ends up in a chimney
An uncapped flue attracts birds, squirrels, and raccoons, and each leaves a different signature. Squirrels are loud, active at dawn and dusk, and often scrabble against the metal damper. Raccoons are heavier, largely nocturnal, and typically take up residence on the smoke shelf rather than in the flue itself.
Birds are the most common and the most consequential. Chimney swifts in particular use chimneys as substitute hollow trees, cementing a small half-cup nest directly to the flue wall with saliva. Their young are noisy in a very distinctive way — a loud mechanical rattling that people frequently describe as sounding electrical.
The legal part nobody expects
Chimney swifts are a native migratory species protected under federal law, and an active nest with eggs or young cannot be removed. This is not a company policy or a professional preference; it is the Migratory Bird Treaty Act, and it applies regardless of how disruptive the noise is.
The practical consequence is straightforward. If swifts are actively nesting, the chimney cannot be used and the nest cannot be touched until the birds have fledged and departed on their own. The correct action is to wait, then clean and cap immediately afterward. Anyone offering to remove an active nest of a protected species is offering to break the law on your behalf.
Why fall is the window
Late summer through fall is when the nesting season ends and the chimney becomes legally and practically clearable. Swifts migrate out, squirrels raised in spring have dispersed, and the flue can be emptied and closed off before winter.
It is also the last comfortable window before the heating season, which matters because you should not burn anything until the flue is confirmed clear. Around Shorewood chimney sweep calls and the neighboring towns, early fall is when most of this work gets done for exactly that reason.
What a nest does beyond the noise
Nesting material is a blockage in the exhaust path, and a blocked flue does not stop working quietly. It pushes smoke and, on any gas appliance venting into the same structure, carbon monoxide back into the house.
Debris also accumulates: droppings, feathers, twigs, and the remains of previous seasons all collect on the smoke shelf where they hold moisture against the masonry and produce a persistent odor. Droppings in an enclosed space carry their own health considerations, which is why removal is done with proper containment rather than a shop vacuum and optimism.
What not to do
Do not light a fire to drive animals out. It kills anything that cannot escape, the material burns unpredictably in a confined flue, and a nest fire in a chimney is a genuine structural fire risk.
Do not open the damper to look until you know what is above it. Opening it drops whatever has accumulated — and occasionally a live animal — directly into the room. And do not seal the top while anything is still inside; trapping an animal creates a considerably worse problem than the one you started with.
Clean, then cap — in that order
The permanent solution is a properly sized cap with a stainless mesh screen, installed after the flue has been cleared. A cap keeps birds, squirrels, raccoons, and rain out while allowing full exhaust flow, and it is the single most cost-effective part on a chimney.
It has to be sized and fitted to your flue, not approximated, and the mesh has to be intact — a damaged cap is functionally no cap. Our chimney caps and crowns page covers the options, and a chimney inspection confirms the flue is genuinely clear before it goes on. Price up front on our pricing page. Insured and bonded, 29 years, 7 days a week from 7 AM to 7 PM at (815) 305-5510.
Frequently asked questions about animals in a chimney
How do I know whether it is birds or a squirrel?
Timing and sound. Squirrels are active at dawn and dusk and scrabble noisily against metal, often at the damper. Birds produce chirping or, with swifts, a loud rattling chatter from nestlings. Raccoons are nocturnal, much heavier sounding, and usually settle on the smoke shelf rather than in the flue.
Can a nest be removed while birds are in it?
Not if the species is federally protected, which chimney swifts are. An active nest with eggs or young must be left alone until the birds leave on their own, after which the flue can be cleaned and capped. Do not use the chimney in the meantime.
How long until swifts leave?
They are present through the nesting season and migrate out afterward, so late summer into fall is when chimneys typically become clear. The birds themselves set the schedule, and the practical approach is to book the cleaning and cap for after they have gone.
Is a nest in the chimney a fire hazard?
Yes. Dry twigs and nesting material sitting in the flue are highly combustible and also block the exhaust path, so a fire lit below can ignite the material and push smoke into the house at the same time. Never burn to test whether a flue is clear.
Will a cap definitely keep animals out?
A correctly sized cap with intact stainless mesh will, which is why it is the standard prevention. Caps fail when they are the wrong size, poorly secured, or the screen has corroded or been damaged, so the cap itself is part of every annual inspection.
What about the smell after the animals are gone?
It usually comes from droppings and nesting debris left on the smoke shelf, which hold moisture and continue to smell long after the animals have left. Clearing that material out is part of the cleaning, and the odor generally resolves with it.
Can I just drop something down to push the nest out?
It is a bad idea. You can compact the material into a tighter blockage, damage the flue liner, or force debris into the smoke chamber where it is harder to reach. It also risks harming a protected species if anything is still alive up there.
Do gas fireplaces have this problem too?
They can, and the consequence is more serious. A blocked vent on a gas appliance can push carbon monoxide back into the house rather than outside. Direct-vent terminals at ground level are especially prone to nests, insects, and being overgrown by landscaping.
Published September 4, 2026 · Last updated August 27, 2026