Chimney Caps, Crowns & Dampers in Northwest Indiana
Four parts sit at the top of a chimney. Each one keeps something out: rain, animals, sparks or cold air.
By Mark Jason, owner of NWI Chimney Sweep · 34 years on NWI rooftops
From the ground, here is how to tell them apart
The cap is a metal hood, the crown a concrete top, the chase cover a metal lid, and the damper a door on the flue.
Cap
The metal hood with mesh sides sitting on the flue tile. If you can see straight down a bare clay tile from a ladder, there is no cap.
Crown
The sloped concrete or mortar surface between the flue tile and the outer edge of the brick. Cracks here are invisible from the yard.
Chase cover
A one-piece metal pan on top of a siding-clad chimney box. Rust streaks down the siding mean it has failed.
Damper
A cast-iron plate in the throat above the firebox, or a gasketed lid at the top operated by a cable.
Caps: mesh, metal and fit
A chimney cap should be stainless steel, sized to the flue tile, with three-quarter-inch mesh and a lid set well above the opening. A single-flue cap clamps to the clay tile with set screws; a multi-flue or custom cap is anchored to the crown and covers everything on top of the stack. We install stainless steel. Galvanized caps cost less on the shelf and begin rusting within a few winters of lake-effect moisture, then stain the crown and brick below them. Mesh is three-quarter inch: small enough to stop squirrels, starlings and embers, large enough not to ice over or clog with soot. The lid has to sit high enough above the flue that it does not choke the draft, which is why a cap bought by guessing the tile size often makes a fireplace smoke.
Crowns: seal it or rebuild it
A cracked chimney crown is sealed with an elastomeric coating if the concrete is solid, and rebuilt if it is loose, flat or crumbling. A proper crown is cast concrete, not leftover brick mortar troweled flat. It slopes away from the flue, overhangs the brick by about two inches with a drip groove on the underside, and leaves a gap around the flue tile filled with flexible sealant, because the tile grows when it heats and a rigid crown would crack around it. Most crowns we see on older chimneys are thin mortar washes with none of those features.
- Hairline cracks, crown otherwise solid: a brushed-on elastomeric crown coating bridges the cracks and sheds water.
- Wide cracks, loose chunks, or a crown that is flat and ponding: it is broken off and a new one is formed and poured with the overhang and slope it should have had.
Coating a crown that is already crumbling only glues the pieces together until spring.
Chase covers on prefab chimneys
A chase cover is the metal lid on a wood-framed prefab chimney, and a rusted one should be replaced with cross-broken stainless steel. Factory-built fireplaces, common in newer subdivisions around St. John, Winfield, Cedar Lake and Lakes of the Four Seasons, vent through a metal pipe inside a wood-framed box. The lid on that box is the chase cover. Builders usually fitted flat galvanized steel; water pools in the middle, the zinc gives up, and the rusted pan drips into the framing and onto the firebox top. The replacement is stainless, cross-broken so the center stands higher than the edges, with a turned-up collar around the pipe and a drip edge over the siding. The pipe’s own storm collar and rain cap go back on above it.
Dampers: throat or top-sealing
A top-sealing damper closes the flue at the top with a gasketed lid, and it replaces a throat damper that no longer seals. The original throat damper is cast iron sitting in the path of rain, soot and heat. They warp, rust at the hinge pins and stop closing fully, and even a good one is metal resting on metal with no gasket. A top-sealing damper moves the closure to the top of the flue: a spring-loaded lid with a silicone gasket, held shut by a stainless cable that runs down to a bracket in the firebox. Closed, it stops conditioned air leaving and keeps rain and animals out. It is meant for open wood-burning fireplaces. It is not fitted over gas logs unless it is locked open, and it is never fitted on a flue serving a furnace or water heater.
Signs something at the top has failed
Water in the firebox after rain, animal noise in the flue, rust stains and cold drafts with the damper shut point to the chimney top. Bits of concrete or mortar on the roof near the stack mean the crown is breaking up. None of the work on this page includes cleaning the flue or scanning the liner, so if water has been entering for a while, expect us to recommend an inspection of the flue and smoke chamber and, where brick has suffered, tuckpointing or brick repair.
What affects the cost
Cap, crown and damper costs depend on flue size and count, the material, crown condition, and how hard the roof is to work on. One standard flue takes a stock stainless cap; two flues, an odd tile size or full coverage means a custom one. Sealing a sound crown is brushwork, while rebuilding one means demolition, forming and a pour. Chase covers are fabricated to the measured chase, so size and the number of pipe holes matter. Starting prices for each item are on the cap, crown and damper price list.
Cap, crown and damper questions
Will adding a chimney cap hurt my fireplace draft?
A correctly sized cap does not. Problems come from lids set too close to the flue opening or mesh clogged with creosote. If a fireplace began smoking right after a cap went on, the lid height or mesh is the first thing to check.
What mesh size should a chimney cap have?
Three-quarter inch is the usual choice here. It blocks birds, squirrels and most sparks without icing up. Finer mesh clogs faster on wood-burning flues and needs checking more often. Whatever the mesh, a chimney cap should be looked at during each yearly sweep, because creosote builds on the wires first.
My crown has hairline cracks. Is that an emergency?
Not today, but it is the cheapest moment to act. Each freeze widens the crack and lets more water into the top courses. A crown coating applied while the concrete is still sound usually avoids a rebuild later. Left alone, a cracked chimney crown lets water into the brick below.
Why are there rust streaks running down the siding on my chimney?
The galvanized chase cover has rusted and rainwater is carrying iron oxide over the edge. By the time streaks show, the pan often has pinholes, and water is reaching the framing inside the chase. A stainless steel chase cover ends the rust for good.
Is a top-sealing damper better than the one in the throat?
For sealing, yes: a gasket against a flat frame closes far tighter than iron on iron. The trade-off is the cable and handle in the firebox, and that it must be opened fully before every fire. A top-sealing damper also doubles as a rain cover.
Birds are nesting in my chimney. Can you remove them and cap it?
It depends on the bird. Chimney swifts are protected under the federal Migratory Bird Treaty Act, so an active nest stays until the young have left, usually by early fall. Afterward the flue is cleaned and capped. Starlings and squirrels have no such protection.
Can one cap cover two flues?
Yes. A multi-flue cap has a base flange that fastens to the crown and a single lid over every flue in the stack. It also shades the crown from rain, which slows cracking. Multi-flue chimney caps are measured and made to fit the crown.
Do special caps fix wind-driven downdrafts?
Sometimes. Wind-directional and vacuum-style caps help when gusts hit a short chimney or one below a taller roofline. They do nothing for downdrafts caused by a cold flue or a house under negative pressure, so the cause has to be identified first.
Missing a cap or seeing rust up top? Call and describe what you see.
A person answers the phone from 7am to 9pm, every day of the week.
Call (219) 203-9797