Filters-NOW DPFU17.5X21X5M8 17.5x21x4.5 - 17.25x20.75x4.38 MERV 8 Rheem Replacement Filter Pack of - 2 Nominal Size 17 1/2 x 21 x 4 1/2 (Actual Size 17 1/4 x 20 3/4 x 4 3/8) Traps&#44; filters reduces major pollutants&#44; such as dust and pollen&#44; from the air passing through Deep-pleat Filters perfectly fit the media cabinet. Surface area is maximized&#44; allowing filters to last up to one year reducing replacement changes. Lasts up to 6 Months