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

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Contractor's Assistant: Did you check the furnace's filters? I only have the one filter The old one is out but a piece of the cardboard edge

furnace filter slot cover FilterLock satisfies the department of energy recommendation that the furnace filter slot be covered to avoid air leaks; Click here to learn more about Eco

diamond bonanza slot cover of that box out When you pull that cover out, you'll see a furnace filter Or maybe you won't Maybe they didn't even have one in there But you will