20x20x5 (19.75x19.88x4.38) Carbon Odor Block Aftermarket Lennox Replacement Filter (2 Pack) Lennox part number X0585 Nominal size 20 x 20 x 5. Actual size 19 3/4 x 19 7/8 x 4 3/8. Carbon impregnated disposable pleated panel filters. This is an aftermarket filter.