What is the pipe coming out of the top of my furnace?
The metal pipe rising out of the top of a gas furnace is the exhaust flue. It carries the burned gas, carbon monoxide included, up the chimney or out the roof. If your furnace has two white plastic pipes instead, it’s a high efficiency furnace, and those pipes do the same job through a wall.
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From one of our jobs
A metal exhaust flue on a basement gas furnace
Right now: Make sure nothing is stored against the flue and every joint is still connected. A gap, rust through or a carbon monoxide alarm, turn the furnace off and call.
A metal flue like this one means a standard efficiency furnace. The exhaust leaves hot, so it rises on its own, and the pipe should climb the whole way with every joint tight and screwed. Rust, a gap or a pipe that sags back toward the furnace needs a look.
A high efficiency furnace cools its exhaust so much it makes water, so it vents through white PVC. One pipe brings outside air in for the burners, the other pushes exhaust out. That cold pipe coming through your basement wall is usually the intake, and it’s supposed to feel cold.
Quick answers
What people ask about furnace exhaust pipes
Why are there two white pipes coming out of my furnace?
That’s a high efficiency furnace. One pipe pulls in outside air for the burners and the other carries the exhaust outside. Keep both ends clear of snow and leaves.
Why is the pipe through my basement wall cold?
It’s most likely the combustion air intake, bringing outside air to the burners. Cold is normal. Frost on the inside or water dripping from it is worth a call.
Is it normal for water to drip from my furnace exhaust pipe?
On a high efficiency furnace, a little water at the outside end is normal. Water inside the house or out of a metal flue is not.
Can a furnace exhaust pipe leak carbon monoxide?
Yes, if a joint separates, rusts through or the pipe is blocked. Every home with a gas furnace needs a working carbon monoxide alarm.
Who inspects furnace vent pipes in Northern Virginia?
Call SwiftPro at (703) 997-9757. We inspect, repair and replace furnace flues and PVC vent pipes across Northern Virginia.
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SwiftPro Heating, Cooling & Plumbing
4230 Lafayette Center Dr N, Chantilly, VA 20151
44679 Endicott Dr, Suite 211, Ashburn, VA 20147
SwiftPro Plumber & Water Heaters
4200 Lafayette Center Dr, Suite N, Chantilly, VA 20151
Virginia Class A contractor license #2705192276