The Holmes Ultrasonic Top Fill Humidifier features a tank design that makes it easy to clean and easy to fill. The ultrasonic humidifier is energy efficient and filter-free, with a virtually silent operation and a 0.36-gallon water tank that propels cool, visible mist for up to 16 hours on its Low setting. This Holmes humidifier includes an aromatherapy tray to use with your favorite essential oils, and is also compatible with Vicks VapoPads Refill Scent Pads. The tank features antimicrobial protection to prevent bacteria and mold growth. The water shortage indicator illuminates when it's time to refill the tank. This portable humidifier is easy to move around your home.