What a chimney cap actually does

It keeps rain, animals and embers out of the flue, and it is the cheapest piece of protection a chimney has.

An open flue is a hole in your roof. Rain goes straight down it and lands in the smoke chamber, where it sits against the mortar and the damper. That is where rust and mortar failure start, and it is why so many expensive chimney repairs trace back to a missing cap.

Animals are the other half. Birds nest in open flues every spring. Raccoons get in and cannot get out. Rats use them as a route into the wall cavity. All of it blocks the flue, which pushes smoke back into the room the next time somebody lights a fire.

The cap also carries a spark arrestor. That is a mesh screen that stops burning embers leaving the top of the chimney, which matters more in Los Angeles than almost anywhere.

Stainless steel, and why it is not optional here

Galvanised caps rust through within a few years near the coast. Stainless does not.

A galvanised cap is cheaper and it looks identical on day one. Two or three years of marine air later it is thin enough to put a thumb through, and it looks fine from the street the whole time.

We fit 304 alloy stainless. It costs more up front and it stops being a conversation after that. In the beach cities and on the peninsula it is the only thing worth putting up there.

Copper is the other option if the look matters. It weathers to a green patina and lasts as long as the chimney does.

How it goes on

1. Measure the flue

   Caps are not one size. We measure the flue tile or the crown opening before anything is ordered.

2. Check the crown

   A cap anchors into the crown or clamps to the flue tile. If either has failed, that gets sorted first or the cap comes loose in the first wind.

3. Fit and seal

   Single flue caps clamp to the tile. Multi flue caps anchor into the crown and cover the whole top.

4. Clear the flue first

   If there is a nest or debris up there, it comes out before the cap goes on. Sealing it in makes things worse.

Signs yours has gone

Rust streaks down the chimney, water in the firebox after rain, or the sound of something moving above the damper.

Rust streaks on the brick are the clearest tell. That is the cap corroding and washing down the stack, and by the time it shows there is not much cap left.

Water in the firebox after a storm means it is going straight down the flue. So does a musty smell that gets worse after rain.

And if you can hear scratching or fluttering above the damper, something has moved in. That needs clearing before a cap goes anywhere near it.