17.5x21x4.5 (17.25x20.75x4.38) MERV 8 Aftermarket Rheem Replacement Filter (2 Pack) Nominal Size is 17 1/2" x 21" x 4 1/2" Actual Size is 17 1/4" x 20 3/4" x 4 3/8" Traps, filters & reduces major pollutants, such as dust and pollen, from the air passing through your heating and cooling systems. Deap-pleat Filters perfectly fit the media cabinet. This is an aftermarket filter.