Nordic Pure 20x25x5L1M12-1 Lennox X6673 Replacement MERV 12 Pleated Furnace Air Filter, Box of 1 Actual size of air conditioner/furnace air filters: 19-7/8 x 24-7/8 x 4-3/8 Significantly reduces dust in home Reduces dust mites, mold spores, pet dander, pollen, smoke particles, and other airborne particulates by up to 97.8%