Quiet Operation for Bedroom Use: Ultrasonic humidifiers are incredibly silent, produces less than 38 dB of noise; perfect for your baby and a disturbance-free sleep at night. 4L Tank Capacity, Works for All Night: Over a gallon of water lasts for 12-30 hour working time on a full tank; designed to humidify the air in rooms up to 10-30 m² / 107-322 ft², bedroom, nursery, office and so on.