By James Rodriguez, Central Chimney Service.
Late summer is when animals start looking for winter quarters, and an uncapped flue is one of the best-insulated, best-protected cavities on your property. Closing it off in August is far easier than dealing with what has moved in by November.
Why an open flue is attractive to wildlife
A chimney is a vertical shaft, dry, sheltered from wind, warmer than outside air, with rough walls that are easy to climb and no predator access. From an animal’s point of view it is close to ideal, which is why this is a recurring problem rather than bad luck.
The three regulars here are birds, squirrels, and raccoons. Birds nest on the smoke shelf or wedge material into the flue. Squirrels use the flue as a route into soffits and attics and sometimes fall in and cannot climb back out. Raccoons, which are strong climbers and comfortable in tight spaces, will use a wide flue as a den.
Why an animal in the chimney is a real hazard
Nesting material is dry, fine, and combustible, sitting directly in the path of hot flue gas. That is the immediate risk. The second is blockage: nests, debris, and remains restrict draft, which pushes smoke and combustion products back into the room instead of up the flue.
The third is what stays behind — droppings, parasites, and odor that persist long after the animal is gone. And the fourth is timing. Chimney swifts are federally protected while nesting, which means an occupied nest generally cannot be removed until the birds have fledged. That is precisely why capping is a late-summer job rather than a spring one.
What a proper cap looks like
A cap is a metal hood over the flue opening with a spark arrestor screen on the sides. Stainless steel or copper is worth paying for; galvanized caps rust out in a handful of Illinois winters and then fail exactly when you have stopped thinking about them.
The screen mesh needs to be fine enough to exclude birds and embers but open enough not to choke the draft or clog with creosote. The cap must be sized and secured to the tile or crown properly — a loose or undersized cap blows off in the kind of storm this area gets every spring. Multi-flue chimneys can take a single full-coverage cap over the whole crown, which also protects the crown itself.
A cap also does quiet work you never notice. It keeps rain off the smoke shelf and damper, which is what prevents the rust behind most chimney-leak calls we take. It reduces downdrafts in windy weather, because the hood breaks up wind blowing straight across the flue opening. And on a multi-flue chimney, a full-coverage cap shelters the crown itself — the component most likely to crack and the most expensive one to recast. For the least costly item in the whole system, it prevents a disproportionate share of the expensive failures.
What to do if something is already in there
Do not light a fire to drive it out, and do not open the damper to see. Both make things much worse. If it is a bird nest and the season is over, or a squirrel that has fallen in, the removal is straightforward from above once someone can see what is there.
Scratching or fluttering above the damper, a strong ammonia or decay smell, sudden draft problems, or debris on the smoke shelf are the usual signs. A chimney inspection identifies what is present before anything is disturbed, and the cap goes on after the flue is clear — never before, or you have sealed the problem in. See our caps and crowns page for options.
Getting capped in Shorewood
Central Chimney Service works throughout Shorewood and the surrounding towns seven days a week from 7 AM to 7 PM. Insured and bonded, 29 years in the trade, and the price is given up front. Call (815) 305-5510.
Frequently asked questions about chimney caps and wildlife
Do I need a cap if I never use my fireplace?
Yes, arguably more so. An unused flue still takes rain straight onto the smoke shelf and damper, and an unused chimney is quieter, which makes it more attractive to animals. The water damage accumulates whether or not you burn anything.
Will a cap hurt my draft?
A correctly sized cap with adequate screen area and proper height above the flue has a negligible effect. Draft problems from caps come from undersized units, screens clogged with creosote, or a cap mounted too low over the opening.
How do I know if there is an animal in my chimney right now?
Listen at the fireplace with the damper closed. Scratching, chirping, or fluttering that follows a daily rhythm is the clearest sign. Other indicators are a sudden strong odor, smoke that will not draw, and nesting debris on the smoke shelf.
Are chimney swifts really protected?
Yes. They are migratory birds covered by federal protection, and an active nest with eggs or young generally must be left alone until the birds leave on their own. Capping after they have gone is the legal and practical way to prevent a repeat.
What happens if an animal dies in the flue?
You get a persistent odor that no air freshener touches, and the remains plus nesting material act as a blockage. It needs physical removal and a thorough cleaning of the smoke shelf and flue, after which the smell resolves.
Can I install a cap myself?
It is roof work at the highest point of the house, which is the main objection. Beyond the fall risk, sizing and secure attachment matter, and a cap that is the wrong size or poorly fastened either restricts draft or ends up in the yard after a storm.
Do gas fireplaces and furnace flues need caps?
They do. Any open vent terminal can admit rain and animals, and gas flue exhaust is acidic, so keeping additional water out of that system matters. Furnace and water heater flues get the same consideration.
How long does a stainless cap last?
A quality stainless cap will typically outlast several galvanized ones and often lasts as long as the crown beneath it. The screen is the part that needs periodic attention, since creosote can accumulate on the mesh and restrict airflow.
Published August 16, 2026 · Last updated August 9, 2026