Filter Monster FilterLock Furnace Filter Slot Seal 2pack

: FilterLock seals one inch furnace and AC filter slots to improve indoor air quality and reduce utility bills Cover for furnace filter Cover for filter slot

I think I'll make a similar cover for my furnace filter slot I see the potential for better return air flow upstairs by restricting leakage

metalen kist met slot Easy to install Seals furnace filter opening; 2-piece overlapping construction; Improves indoor air quality; Saves energy; Fits up to 25” opening; Residential

metalen kast met slot Reduce energy consumption & prevent harmful airborne pollutants from entering your home with FilterLock by AllergyZone Works with most 1 furnace filters