Chimney Spark Arrestor Installation in Los Angeles

A wood fire lifts burning fragments up the flue on the draft. Most burn out on the way; some are still glowing when they reach the top. A chimney spark arrestor is a metal mesh, sometimes called an ember screen, sized so that fragments large enough to start a fire are held back while smoke and gases pass through. Held against the mesh, an ember keeps burning until it is too small to matter.

It is a reduction, not a seal. Mesh fine enough to stop every particle would choke the draft, so the opening size is a compromise between ember control and airflow. Where a specification applies, it comes from the local fire authority, which is the right place to check rather than a product label.

It also does nothing for a fire that is burning inside the flue. Creosote that ignites is dealt with by cleaning the chimney before it builds up, not by the screen at the top.

On most chimneys the spark arrestor is the mesh sides of the cap. The hood keeps rain out; the mesh keeps embers in and, if it is sturdy and well fastened, keeps animals out as well. One part does all three jobs, so most people buy one thing.

Which cap to choose, and in which material, is covered on chimney cap installation. This page covers the mesh itself: whether it is doing the ember job, whether it is intact, and whether it is clear. If you are mainly worried about birds and squirrels, the fastening matters more than the mesh size; see chimney animal screens.

Factory-built chimneys are a separate case. Their termination cap is part of the manufacturer's listed system, and a replacement or spark arrestor for one should be a component the chimney manufacturer specifies, not a generic part.

The mesh is the coolest, narrowest point the smoke passes through, so it is where deposits collect first. On a wood-burning flue, creosote, the tarry residue of incomplete combustion, can coat the wires until the open area is a fraction of what it was. The fire then draws poorly, burns cooler, and produces more creosote, which is a loop that ends with smoke in the room.

A clogged screen is rarely the only deposit. If the mesh is plugged, the flue below it usually needs attention too, and chimney cleaning covers that. Where the deposit has turned hard and glossy, glazed creosote removal is a different job. NFPA 211 calls for annual inspection, with cleaning as condition requires, and the screen is part of what gets looked at.

Burning dry, seasoned wood reduces how fast the screen plugs. The EPA Burn Wise program has practical guidance on that. If smoke is already coming into the house, this explanation of indoor smoke walks through the other causes.

California maps wildfire hazard by address. The Office of the State Fire Marshal publishes the Fire Hazard Severity Zone maps, and you can look up which zone your property falls in. Neighbors on the same street can sit in different zones.

What a zone means for your chimney is set locally. Local fire authorities may require a spark arrestor on a wood-burning chimney, may specify the mesh, and may check it during a defensible-space or property inspection. Because those rules differ between jurisdictions and change over time, this page does not quote a dimension. Ask your local fire department or building department what applies at your address, and tell whoever fits the screen what they said.

If you have been told your chimney needs a compliant screen after an inspection, keep a copy of whatever the inspector gave you. It is the specification the new screen has to meet.

Parts of Los Angeles County put houses right up against brush: canyon roads, hillside streets, foothill neighborhoods where the back fence is chaparral. Where a chimney sits close to dry vegetation, a wood-shake roof, or a yard full of leaf litter, an ember leaving the flue has somewhere to land.

Wind makes it worse. Dry offshore winds carry embers further and dry out everything they might land on, which is why the mesh at the top of the chimney matters more on a hillside than it does on a flat street far from open land. On those days, whether to light a fire at all is a question for your local fire authority's guidance, not the screen.

Salt air corrodes mesh on coastal houses too, and corroded mesh fails as an ember screen before it fails as anything else. The coastal corrosion side is covered on chimney cap replacement.