Missing Chimney Rain Caps
and Spark Arrestors
An open flue is a straight pipe from the sky to your firebox. The cap on top keeps out rain, birds and leaves, and its screen keeps embers on the chimney.
The chimney flue had no rain cap at 21 of Russ’s recent inspections. A couple more had a cap with the spark arrestor screen missing or a cap that was damaged. A Vancouver report summed up what the cap does: it keeps water, debris and animals out of the flue, which can damage the chimney inside and lead to blockages.
It’s a small part. The water it keeps out is what wears the inside of a chimney.
What falls down an open flue
Rain, first. In a Portland winter that’s a lot of water, landing on the smoke shelf and the damper and soaking into the brick. A Portland report traced moisture staining on the firebrick and moderate rust on the damper to water coming down the flue, likely from missing rain caps or a compromised crown in the past.
Then leaves and needles, and birds. A bird nest in a flue is a blockage, and a blocked flue is the last thing you want when someone lights a fire.
The spark arrestor
Most caps include a mesh screen around the sides. That screen is the spark arrestor. It stops embers from leaving the chimney and landing on the roof, a cedar fence or the fir tree hanging over the house. A Battle Ground report found a metal cap with the mesh missing and recommended a qualified chimney contractor install an approved stainless steel screen.
Screens clog with creosote on chimneys that get used a lot. A sweep cleans them during a regular sweeping.
Caps, crowns and the rest of the top
The cap sits on the flue. Around it is the crown, the concrete or mortar slab that sheds water off the top of the chimney. Cracked crowns are their own problem and have their own chimney crown post. An older chimney may have an unlined flue, which the unlined flue post covers. Gas appliance vents through the roof are a separate system; the gas vent pipe post covers those caps.
Real Inspection Photos
Chimney Cap Findings From Russ's Inspections
Rain cap and spark arrestor findings from Russ's recent reports.
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Two open flues with no rain cap. -
A metal cap with no spark arrestor screen around it. -
An open flue, with moss growing on the crown around it. -
No rain cap on this Beaverton chimney.
What Russ checks
He looks at the chimney top from the roof when it’s safe to walk, or by drone when it isn’t. He notes whether each flue has a cap and screen, and looks at the crown and flashing. Inside, he looks at the firebox and damper with a light. He doesn’t climb chimneys, remove caps or run a camera down the flue. That’s a Level 2 chimney inspection by a sweep, and the Level 2 post explains when buyers order one.
- From the yard, look at the top of each flue for a metal cap
- Check for mesh on the sides of the cap
- Look in the firebox for water stains, rust or debris
- Listen for birds in the chimney in spring
- Ask when the chimney was last swept
A missing rain cap came up at 21 of Russ’s recent inspections. An open flue lets rain, debris and birds fall straight into the chimney, and a missing screen lets embers out. A chimney sweep can install a cap sized to the flue and look at the liner while they’re up there.
For the full chimney picture, see chimney inspections in Portland. To set up an inspection, you can book online.
Chimney Cap FAQ
