Honeywell HC22A 1007 Humidifier Pad, 2-Pack The "heart" of your whole-house humidifier, the Water Panel (also known as humidifier filter, water pad, evaporator pad), should be changed at least once per heating season. The pad is constructed of an expanded aluminum honeycomb mesh that is dipped in a clay coating. This coating is able to absorb and hold water. Warm, dry air is forced through the wet pad to introduce water vapor into the home. Product Features: Factory original OEM part Dimensions approximately - 9 13/16" x 9 1/2" x 1 1/2" Pad change instructions are printed on product carton Fits the Following Humidifiers: Honeywell HE220A Honeywell HE220B Honeywell HE225A Honeywell HE225B Honeywell HE100A Honeywell HE150A Humidifier water panels (sometimes referred to as a filter) are a regular replacement item in whole-house humidifiers. For the best performance we recommend that the Water Panel be replaced once a year, either prior to the start or at the end of the heating season. If you have especially hard water - the panel can be replaced 2 times per year. Click here for instructions on changing out your water panel