My furnace has two 1 filter slots Should I use both slots?

AllergyZone FilterLock Furnace Filter Slot Seal Door Cover furnace filter slot cover Furnace Filter Direction? How to Replace Furnace Filter · Furnace Filter Slot Cover: Easy Fix to HVAC Air Leak · Indoor Unit Will Not Turn Off: Why Does My furnace filter slot Magnetically attaches to ductwork to cover furnace filter slot door Two-piece design works with any 1-inch furnace filter up to 25 inches long Universal one-

jogar slot A lot of HVAC air handlers do not have covers over the filter slot and this is costing homeowners