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Pellet Vent, Done to Code: Pipe Type, Termination & the Mistakes That Smoke
Which pipe a pellet stove actually requires, the venting configurations that work, clearances, and the install mistakes that cause smoke and CO.
By Gus Halloran ·
Pellet stoves are forgiving appliances attached to unforgiving physics: they vent under fan pressure through a small pipe, and every shortcut in that pipe shows up as smoke smell, soot, or a CO alarm.
The pipe itself: PL vent, nothing else
Pellet stoves use listed pellet vent (“PL” / type L) — double-wall pipe with a stainless inner liner, sealed joints, typically 3” or 4” diameter. Not single-wall stove pipe (it’s for natural-draft wood stoves), not B-vent (gas only), not dryer duct (please). The exhaust is pushed by a combustion blower, so joints see positive pressure — which is why pellet vent twist- locks and gaskets matter: any leak leaks outward, into the room.
3-inch vs 4-inch follows the manual’s math: total equivalent vent length (each 90° elbow counts ~5 feet) and altitude. Long runs and high elevation push you to 4”; guessing 3” on a long run is how stoves smolder at shutdown.
Configurations that work
The classic and best: out and up — horizontal through the wall, tee with a cleanout, then a vertical rise outside. The rise adds natural draft for power outages, and the cleanout makes annual ash removal a five-minute job. Straight-out horizontal installs are legal per most manuals but dump exhaust at ground level and backpuff smoke when the power dies mid-burn — a vertical section is cheap insurance.
Clearances and termination
Pellet vent typically needs 3 inches to combustibles (per its listing — read the pipe’s, not the internet’s), a listed wall thimble through framing, and termination rules that exist for your neighbors and your own air intakes: commonly 4 feet from doors/windows/inlets, above snow line, and never under a deck or soffit that traps exhaust. Cap with the listed horizontal cap, angled to shed rain.
The mistakes installers see weekly
Sloping horizontal runs down toward the stove (condensate and ash creep back), skipping the outside air kit in tight houses (starved fires, dirty glass), unsealed joints “because it’s under fan pressure anyway” (exactly backwards), and reusing an old masonry chimney without a liner sized to the stove. And one non-negotiable: a CO alarm in the same room — a pellet stove is a combustion appliance with a computer, and computers fail.