It’s a backup, not for primary combustion air.
This damper is not for primary combustion air. Your furnace should still breathe outdoor air almost all the time.
Safety
Safety limits, in plain language
Read these before you buy or install the damper.
Not for small, closed-off rooms.
Do not install it in a confined space with less than 50 cubic feet of space for every 1,000 BTU/h of all the gas appliances in the space (ANSI Z223.1 / NFPA 54, 9.3.2.2). A 100,000 BTU/h furnace needs 5,000 cu ft, about a 25' × 25' room with 8' ceilings. If you’re unsure, ask an HVAC tech.
Homes only.
It’s for residential use.
Keep the intake clear anyway.
The damper keeps the furnace running through a blockage. You still need to clear the snow.
EfficiencyMax Furnace Backup Intake Damper only handles the intake.
A blocked exhaust pipe, a frozen condensate line, or a failed pressure switch can also shut a furnace down. This part doesn’t fix those.
Install only on the intake pipe.
Do not install this on the exhaust or vent. If the intake is ABS, use ABS fittings and cement.