Honeywell - TRN2321T1 Trane Perfect Fit Replacement Filter 23.5" x 21" x 5" Long Life - up to 1 year Size: 23.5" x 21" x 5" Efficiency Rating: MERV 10; Catches particles as small as 0.3 microns Fits: TFM235BOAHO Pressure Drop at 500 fpm: 0.17 in. w.c.