Does my concentric furnace vent need a cap?
Concentric furnace vents need a cone around the fresh air intake to stop rain from pouring directly into the furnace. While leaving them uncovered allows mice to crawl inside and block the exhaust fan, adding aftermarket covers with small holes can cause the vent to ice over and trap dangerous exhaust smells in the house.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Checking if a drain line is present before the furnaceDid this help you?
- 2Measuring the height of the exhaust over the intake to see if a cap will fitDid this help you?
- 3Fabricating a custom cover out of stainless hardware clothDid this help you?
- 4Friction-fitting a cut circle of mesh inside the pipeDid this help you?
- 5Using 1/2-inch square chicken wireDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Just noticed my furnace exhaust and it doesn’t have a cap on like I’d expect to see on most concentric vents.”source ↗
“Does it look like this was needs a cap to prevent water from getting into the intake?”source ↗
“Yea that needs to have a cone around the fresh air or else rain is gonna just be pouring into your furnaces if you don’t have a drain on it before the furnace”source ↗
“Last year a mouse crawled into the exhaust vent and brought my gas furnace down by getting chopped up and blocking the exhaust fan.”source ↗
“I bought one of these “furnace vent covers” on Amazon, but the holes seem awfully small and perhaps prone to ice over?”source ↗
“I noticed my basement started smelling of exhaust. Definitely not a good thing! I’m taking it out.”source ↗
Where this came up
People with this problem also raised
- 3Is a chimney cap necessary to stop leaks and animals?
- 4How to stop birds from nesting in high dryer vents without cleaning a clog
- 14Why is my ductwork dripping condensation inside the walls?
- 2Why is water blocking my Bryant HVAC exhaust pipe?
- 11Gap around furnace b-vent after roofing
- 3Why is water pooling inside my furnace?