Compact water chamber holds 350 mL of water, yet the efficient performance of the humidifier allows it to last the night. HumidControl feature ensures a consistent temperature difference between water and ambient air to minimize condensation in the tubing and keep humidification level constant throughout the night. Space-saving design adds only 3 inches to length of any GoodKnight 420/425 sleep therapy device. Features rotary button that allows patients to adjust heating level.