Why Do Animals Keep Getting Into My Old Chimney Flue?

What's actually going on

You've got animals in your flue because the top of your chimney is open. Either there's no cap, or the one that's up there rusted through, blew off, or has mesh gaps too big to stop anything.

This is one of the most common calls we get on older homes. Chimneys built before the mid-1970s were routinely finished with bare clay flue tile and nothing over it. To wildlife, that's a warm, sheltered vertical hole, basically a hollow tree with better insulation.

The fix is genuinely simple: get whatever's living up there out, then put a proper stainless cap on. The catch, and it's a big one, is the order. Cap first and you trap the animal inside.

So before you buy a cap, figure out what's in there and how to get it out.

Why older homes especially get this

The single biggest reason is that the cap was never there to begin with. Masons in the 1950s and 60s often just left the flue tile exposed. It vented fine and nobody thought about squirrels.

The second reason is failed hardware. Somebody added a galvanized or painted-steel cap in the 80s or 90s, it rusted from the inside, and the screen crumbled. From the ground it still looks like a cap. Up close it's a rusty ring with holes.

Wind and branches take out plenty of caps too. Friction-fit caps clamp inside the tile with a couple of screws, and a heavy limb or a stubborn raccoon can knock one clean off.

There's also the sneaky one: a cap that's present but wrong. Some older mesh has openings over an inch, which stops leaves but not chipmunks or starlings. It's capped in name only.

• Bare clay flue tile, no cap (classic pre-1975 construction)
• Rusted-out galvanized or painted-steel cap with a failed screen
• Cap blown off or knocked loose, possibly sitting in your gutter
• Cap present but mesh openings too large to exclude small animals
• Cracked crown letting animals in beside the cap instead of through it

Figure out what you're dealing with

The sound tells you a lot. Rapid, panicky scratching low in the flue usually means something fell in and can't climb the slick tile back out. That's often a squirrel or a bird.

Rhythmic thumps, chirping babies, or activity at dawn and dusk points to raccoons, which love to den in flues and have their young there in spring.

A soft chittering or a rattling, mechanical-sounding call in summer is often chimney swifts. These birds are federally protected, so if that's what you have, you legally can't disturb them until they've left, usually by early fall.

If you hear nothing but you smell something foul, an animal may have already died in there. That's a removal job, not a capping job.

How to handle it, step by step

Start by confirming the flue is or will be empty. For a squirrel or bird that fell in and can't climb out, drop a thick, knotted rope down the flue and secure the top. Most will climb it and leave within a day. Take it out and cap after.

For raccoons, don't play hero. A mother with kits will defend them, and they carry rabies and roundworm. Call a wildlife removal tech; expect $150 to $400 depending on your area and whether there are babies.

Once you're sure it's empty, measure your flue tile. For a single-flue cap you measure the outside dimensions of the tile that sticks up above the crown. Write down length, width, and how high the tile projects.

Buy a 304 or 316 stainless steel cap sized to your tile. Skip anything galvanized or painted; the whole point is to not repeat this in ten years.

Install it by sliding the cap over the tile and tightening the set screws until it's snug. It should not wobble. If your tile is cracked where the cap clamps, stop and get it repaired first.

Finally, if anything lived in the flue, have it swept and inspected. Nesting material and droppings above the firebox are a fire hazard and a CO risk.

What it costs in 2026

If you're comfortable on your roof and it's a straightforward single flue, this is a cheap fix. Add a tube of high-temp sealant and a screwdriver and you're done.

Hiring it out lands between $250 and $1200 for most homes. That covers the cap, safe roof access, proper sizing, and the labor to fit it. Steep or high roofs push toward the top of that range because of fall-protection setup.

Animal removal is usually billed separately. Wildlife techs charge roughly $150 to $400, more if there are babies or if they need to make multiple trips to confirm the flue is clear.

If the flue needs sweeping because something nested in it, add $150 to $300 for a standard chimney cleaning and Level 1 inspection.

Crown repair, if your concrete is cracked, is the wild card. Minor crown sealing might be $200 to $500; a full crown rebuild can run $1,000 to $3,000. Get that assessed before you assume it's just a cap.

• Professional repair typically runs $250–$1200. This is not a DIY job, so plan on hiring a pro.
• Pro cap supply and install: $250–$1200
• Wildlife removal (separate): $150 to $400
• Flue sweep and Level 1 inspection: $150 to $300
• Crown seal or rebuild (if needed): $200 to $3,000

Should you DIY it?

The cap install itself is genuinely DIY-friendly on a single flue with a walkable roof. Measure, order, slide it on, tighten set screws. Most people finish in under 20 minutes once they're up top.

The part that isn't DIY-friendly is getting there. A one-story ranch with a 4:12 asphalt roof on a dry day is one thing. A two-story with a 9:12 pitch, or anything wet or mossy, is where people get hurt. Rent a harness or hire it out.

Skip the DIY route entirely if you've got multiple flues clustered on one crown. A multi-flue top-mount cap needs proper measuring and anchoring, and a poor fit lets rain and animals right back in.

And leave the animals to a pro if you're hearing raccoons. It's not a fair fight, and the disease risk isn't worth saving a couple hundred bucks.

Can this wait?

If something is trapped and scratching right now, no. That animal is either going to die in there or claw its way toward your living space. Deal with it today.

If the flue is open but currently empty and you're not using the fireplace, you've got a little breathing room, but not much. The next animal is one cold night away, and rain is doing damage the whole time it's uncapped.

If you're heading into winter and use the chimney, don't wait. A blocked flue from a nest can back carbon monoxide into the house, and that's the kind of problem you don't get a second chance with.

The honest answer: this is a high-urgency fix that happens to be cheap. There's no good reason to sit on it.

Older-home quirks to expect

On pre-1970s masonry chimneys, the flue tile sizes can be oddball. You might find a 12x12 or an old 8x13 that modern stock caps don't cover cleanly. Measure carefully and be ready to order an adjustable or custom cap.

Old crowns are often cracked or spalling. Water's been sitting on that concrete for decades. Check it while you're up there, because a bad crown lets animals in beside the cap no matter how good the cap is.

Many older homes also have unlined or terra-cotta-lined flues that were never meant for a modern fire. If an animal nested in there and you plan to burn, get a Level 1 inspection before your first fire of the season.

One more thing on old chimneys: sometimes there are two or three flues sharing one stack (one for the fireplace, one for the furnace or old boiler). Cap all of them, not just the obvious one.

Timing the fix

Spring through early summer is peak nesting season. If you cap then, you're most likely to trap babies. Get animals out, but be extra sure the flue is clear before sealing.

Late summer, after the young have left, is the ideal window to cap. Everything's grown and mobile, and you're set before the fall rush of animals looking for winter dens.

Fall is when squirrels and birds start scouting warm spots. An uncapped flue in September is basically an open invitation for the season.

Winter brings the fall-in problem: an animal drops down for warmth, hits cold smooth tile, and can't climb out. If you hear frantic scratching in January, that's usually what's happening.

How we diagnose this

When we get this call, we start from the ground with binoculars or a zoom lens before anyone touches a ladder. in most cases of the time we can see the missing or rusted cap from the driveway.

Next we listen and ask about timing. What time of day is the noise, is it constant or intermittent, and when did it start. That narrows the species and tells us whether it's a fall-in or a nest.

On the roof we check three things: the cap or lack of one, the mesh size if a cap exists, and the condition of the crown around the flue. Any one of those can be the entry point.

We confirm the flue is empty with a light and a mirror or a phone before we cap anything. Nobody wants a callback because we sealed a raccoon in.

If there's evidence of nesting or droppings, we recommend a sweep and Level 1 inspection so the first fire of the season doesn't ignite leftover debris. Then we size and fit a stainless cap and call it done.