The 70 hour Ultrasonic Cool Mist Humidifier guards against problems caused by dry air in the home. It features an easy to fill 1 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. The humidifier emits a soothing cool mist, and a low water indicator light lets you know when it's time to refill the water tank. Night light feature makes it a great addition to kids' rooms. 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 speed, also depends on atmospheric conditions.