The Aprilaire 35 Water Panel is an OEM replacement for Aprilaire whole-home humidifiers 600, 600A, 600M, 700, 700A, 700M, 760, 768, 350, 360, 560 and 568. The Aprilaire 35 water panel should be replaced at least once per season. However, if you have hard water it may need to be changed more frequently. When a humidifier’s water panel needs changed, most humidifiers have a light to let you know maintenance needs to be performed. The #35 water panel by Aprilaire is sized at 10″ x 13″ x 1 3/4″ and is made in the USA.