20x26x5 (20x25.5x4.38) MERV 13 Aftermarket Lennox Replacement Filter (2 Pack) Nominal size 20" x 26" x 5". Actual size 20" x 25 1/2" x 4 3/8". Pre-applied gasketing on the assembled filter prevents air by-pass. 98% efficient filtration media. This is an aftermarket filter.