The Skuttle 45SD humidifier is a drum type bypass style humidifier that can be installed on either the supply or the return duct system of your home or office. This is a very reliable model that is extremely popular with our clients. You will find the most common parts for your Skuttle 45SD on this page. The humidifier filter on your Skuttle 45SD humidifier must be replaced at least once per year for optimum performance and to increase the life of your humidifier and heating equipment.