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 2 gallon tank, ideal for use in medium to large rooms. 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. It has an optional aromatherapy tray so a few drops of essential oil can be added to create a relaxing atmosphere. 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.