Fits   Aprilaire Models 110, 220, 500, 500A, 500M, 550, 558
*The heavy-duty aluminum mesh frame holds its shape over the life of the water panel as the porous ceramic-type coating absorbs water and maintains the proper level of hydration to support the evaporation process. Water is vaporized as air warmed by the furnace passes over the water panel. The humidified air is carried through the house through the air ducts. Replace water panel annually