IN THE PAST I HAVE ALWAYS BEEN TAUGHT THAT GAS HEATERS IN CLOSETS MUST BE HARD WIRED. RECENTLY I HAVE BEEN SEEING THEM CORD AND PLUG CONNECTED(20A RECEPT WITH APPLIANCE CORD) AND HAVE BEEN TOLD THAT THIS IS PERFECTLY LEGAL. DOES ANYBODY KNOW FOR SURE? IF SO PLEASE STATE CODE REF.