Keep your whole-house humidifier running efficiently with this 2-pack humidifier water filter pad designed to support consistent indoor humidity during the heating season. Compatible with Aprilaire humidifiers 110 / 220 / 500 / 500A / 500M / 550 / 550A / 558 and replacement water panel replaces Aprilaire 10. The heavy-duty aluminum mesh frame is built to hold its shape, while the porous ceramic-type coating absorbs water to maintain proper hydration for the evaporation process. Honeycomb-style filtration helps trap mineral pollutants found in water to reduce scale and help prevent minerals from entering your home’s air. Each panel measures 9 1/2 in x 9 7/8 in x 1 5/8 in and installs easily by removing the old pad and inserting the new one; when changing the panel, slide the water panel into the scale control insert with the colored marker up. For optimum performance, replace about every 6 months or more often in hard water areas; packaging may vary between retail and OEM. Disclaimer: This is not an Original Equipment Manufacturer (OEM) product, HQRP branded product is a replacement. All brand names and logos are registered trademarks of their respective owners. Any use of the brand names or model designations for this product are made solely for purposes of demonstrating compatibility.