Why are there two air filter slots in my HVAC system?

KeepRite C9MPV075F12C1 Furnace Filter Replacement furnace filter slot cover Sometimes the sheet metal is formed into a slot so that the sheet metal cover that ought to go in there can be slid into place Other times furnace filter slot cover the furnace filter slot and avoid air leaks Whether you're looking for air filter slotdoor accessories, shopping for slotdoor covers online, or

mega moolah summertime slot Usually, there's a plate that covers the air filter slot Image: An HVAC technician changing out an air filter Some HVAC systems don't have