Tired of dry air in your home? Humidifiers add moisture and help reduce the risk of illness. Keep your humidifier running at peak efficiency with the GeneralAire 990-13 replacement filter. This handy replacement filter features a unitized frame to maximize pad life and humidifier reliability. The metal pad is coated with clay for optimal water absorption . To ensure proper performance of your humidifier, filters should be replaced once per year. This filter is compatible with 709, 990, 1040, 1042, 1137 and SL16 series humidifiers.