LifeSupplyUSA Humidifier Filter Water Panel Pad for Aprilaire Humidifier Furnace Fits Furnace humidifier Models 400, 400A, and 400M. Compare to Aprilaire Part # 45 Fits furnace humidifier models 400, 400A, and 400M. Compare to Aprilaire Part # 45 For optimum performance replace twice a year at the start and end of the heating season 12.9 x 10.2 x 7.7 inches Brand New Individually Sealed By LifeSupplyUSA