This Packaged Duct Heater is made using a galvanized steel compartment with 1/2″ fiberglass insulation and hinged cover. Features door interlock disconnect switch, primary automatic reset temperature limit control and load carrying secondary over temperature protective device. Includes definite purpose magnetic contactor, differential pressure fan interlock switch. 24V step down transformer. Permanently attached wiring diagram on inside of terminal compartment cover. Galvanized steel element rack must always be 1″ shorter than duct height and 1/2″ shorter than duct width to allow insertion clearance. UL listed. 1 Year Limited Warranty.