Air-O-Swiss Refurbished 7145 Ultrasonic Humidifier - Cool Mist Humidifies the air in rooms up to 540 sq ft (50m) Transparent water tank (water level clearly visible) Industrial strength titanium membrane surface, the quality of which guarantees fast dispersal of mist into the air, ensures long lasting use Hygrostat and mist output regulator for controlled humidification Very energy-efficient