The Skuttle A04-1725-045 Humidifier Evaporator Pad is the replacement evaporator pad for the Skuttle 55-UD Flow-Through Under Duct Humidifier. This filter features a honeycomb filtration design that traps mineral pollutants found in your water and prevents them from being evaporated into the air. Plus, a felt board wick ensures even water distribution for uniform humidifying throughout your home. For optimal performance, you should replace this pad every 6 months or more frequently if you have hard water. This evaporator pad measures 12.75 inches high, 11 inches wide, and 1.75 inches deep.