I had a new ducted heat pump system installed last year, including a new air handler. The old air handler/furnace used 16x20 inch filters and the new one takes 18x20 inch filters. And I still had a box of 5 new 16x20s on hand.
I learned it would be safe to use the narrower filters in the new air handler so I "made" an adapter to increase the filter width from 16" to 18". Not much to it other than a 2"x20" board, duct tape and masking tape. Duct tape secures the board to the filter, masking tape is to seal the top side to stop air from leaking past.
I'll be able to use $40 worth of filters now that otherwise would have been a loss. I change out the narrower filters on a more frequent basis. I put in a new filter today.
Had a big problem with chick-dust clogging the filter when the chick brooder was in the living room. LOL
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