Cool Mist Ultrasonic Humidifier, .66 gal, QC99786 Sale! This item is currently on backorder but you can still purchase it now and we'll ship as soon as more become available. Adds moisture to the room to prevent dryness and irritation. Ultra quiet operation with variable mist output and run time up to 24-hours. Water tank capacity .66 gallon. No filter required. For medium sized rooms.