You must get the conversion kit which is an orifice and gasket(s),springs, or possibly a whole new gas valve--call the manufacturer, or a wholesale plumbing/heating supply warehouse and they'll be able to find you the part number, or point you to someone who has it---keep asking, and someone in the industry will eventually help you....the correct orifice,gaskets/springs are needed because there is a very precise pressure and flow of gas needed for both natural and propane gas