The 120-hour Ultrasonic Warm and Cool Mist Humidifier guards against problems caused by dry air in the home. It features an easy to fill large 7.5L tank, ideal for use in medium to large rooms. Unlike other humidifiers that grow slimy mold on the water tank surface, Silver Clean Protection is embedded in the tank to fight the growth of mold and mildew on the surface of the water tank. Thanks to ultrasonic technology, it disperses a fine mist into the air, and is ultra-quiet making it ideal to have on while you sleep. The humidifier is equipped with the option for warm or cool mist and 3-speed settings. A low water indicator light lets you know when it's time to refill the water tank. It also features a soft glow night light, and a timer. PureGuardian humidifiers create a better home environment for those suffering from colds, allergies and dry skin. Note: Run time is based off of running the unit on low setting and cool mist, also depends on atmospheric conditions.