What Is Sealed Combustion?

Sealed combustion draws combustion air from outdoors through a dedicated pipe and vents exhaust through another, so the burner never uses indoor air. It contrasts with an atmospheric appliance, which takes air from the room it stands in and vents up a conventional flue.

Also called: direct vent · two-pipe combustion

Why it matters to you

Sealing matters more as houses get tighter. An atmospheric appliance in a tight or depressurised space can backdraft, pulling combustion products into the house instead of up the flue. Sealed combustion removes that interaction entirely.

What to do about it

Keep both the intake and exhaust terminations clear outside — of nests, vegetation, and anything that might block them. Blocked terminations are a common cause of lockouts on sealed-combustion equipment.