The Skuttle 39 humidifier is a whole house humidifier designed to be installed on a forced air heating system for a home or office. Maximum humidifier efficiency depends upon the tightness of your home, the hardness of your water and a variety of external factors. Consult us for the Skuttle home humidifier that's best for you. The humidifier filter on your Skuttle 39 humidifier must be replaced at least once per year for optimum performance and to increase the life of your humidifier and heating equipment.