The Cool Mist ultrasonic humidifier has a 1.4 gallon tank capacity tht can operate continuously for up to eight hours. Automatic shut off function allows you to set this humidifier and not have to worry about when to turn off. Water indicator light lets you know when you need to refill the tank, and adjustable mist volume control lets you customize this humidifier to your own specific needs. The easy to fill water tank is simple and removable for fast refill and easy cleaning.