84 Ton Heavy Oil Fired Steam Boiler - 2 Tons Of Oil Fired Steam Boiler Fuel Cost. 80 tons of gas steam boiler. 4 ton gas fired steam boiler - Industrial boiler Steam boilers operate at a higher temperature than hot water boilers, and are inherently less efficient. 80% for a gas-fired steam boiler, 84% for an oil-fired hot water boiler and 82%