Lennox X6669 MERV 16 Filter - 21" x 26" x 4" - Genuine Lennox Product Filter dimensions: 21"x26"x4" Fits the PCO-20C PureAir unit Uses a MERV 16 pleated filter to capture extremely small airborne particles This filter only needs to be replaced every 6 months Genuine Lennox OEM Furnace Filter