HQRP 2-Pack Water Filter for Aprilaire 45 fits Aprilaire 400 / 400A / 400M Humidifiers Coaster HQRP&reg; 2-pack Humidifier Water Filter plus HQRP&reg; Coaster; Compatible with Aprilaire 45 Replacement; 400, 400A, 400M Humidifiers; Dimensions: 10"x13"x1 3/4"; For optimum performance, panel should be replaced every 6 months; 2 weeks DOA replacement warranty!