This transformer is designed to use with Hayward Universal H-Series Low NOx induced draft heater H150FDN, H150FDP, H200FDN, H200FDP, H250FDN, H250FDP, H300FDN, H300FDP, H350FDN, H350FDP, H400FDN, H400FDP. Also fits Hayward Universal H-Series and Low NOx induced draft heater models H200FDP, H300FDN, H400FDP. Also compatible with Hayward Pool and spa hot tub and Universal H-Series gas heater models H250IDL2, H350IDL2, H400IDL2, C_PAHEAT. 120/240-volt-24-Volt ac. New part incorporated on all IDL heaters built after 9/20/04; Weighs 58-pound.