The Skuttle A04-1725-053 is the correct replacement media for the following humidifier models:
The Skuttle Replacement Media A04-1725-053 is a replacement water filter pad for the Aprilaire 110, 220, and 550 humidifier models. These evaporator pad filter will capture mineral pollutants in water, resulting in clean and moist air distribution in your home. This water panel filter is a genuine Skuttle humidifier replacement part and will have your Aprilaire humidifier operating at peak efficiency.
Skuttle Replacement Media A04-1725-053 specifications: