I have been wrestling with this for a week and finally I managed to turn this gas furnace into a coke fired furnace. I have been able to melt silicon bronze with 40# of coke in the furnace and 2 gallons of gasoline in the generator that runs the blower. It takes about 2 1/2 hours to melt. The trick is to burn the coke evening around the pot and keeping the pot from dropping. Propane and natural gas would cost more and require less of my attention. This has been frustrating, to say the least, but I enjoy the struggle.