The 100-hour Ultrasonic Cool Mist Humidifiers guards against problems caused by dry air in the home. It features an easy to fill large 1.5 gallon tank, ideal for use in medium sized 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. Smart mist sensor monitors the level of humidity in the room and adjusts to your selected level. The humidifier is equipped with an easy to use digital display, a night light, timer and 3 speed mist control. A low water indicator light lets you know when it’s time to refill the water tank. Pure Guardian 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 speed, also depends on atmospheric conditions.