Lennox X8788 MERV 16 Filter (2 Pack) Filter dimensions: 20" x 26" x 5" (actual Size 20" x 25-1/2" x 4 3/8") Fits the PCO20-28 PureAir unit This filter only needs to be replaced every 12 months Perfect for people who suffer from allergies, asthma or for people who just want to breathe healthier air Genuine Lennox OEM Furnace Filter