Aprilaire - This replacement water panel evaporator fits models 500, 500A, 500M, 550, 550A, 558, 110 and 220. Water panel evaporators are the heart of your humidifier, designed specifically to deliver the proper humidity necessary to keep you comfortable throughout the heating season.

• Water panel slides into the scale control insert, and the water distribution tray sits across the top of the panel
• Water panel measures 9-3/4" x 10" x 1-3/4"
• Replace annually
• Designed to last the entire heating season