Burnham Commercial has announced the 4S Four-Pass Wetback Scotch Boiler, available in sizes to 800 hp for high and low pressure steam or hot water. The Series 4S incorporates positive water flow circulation and maximum heat transfer from water-backed surfaces. The 4S design features high furnace volumes, resulting in low furnace volumetric release rates. It also has an innovative, high-tech rear access door that incorporates a lightweight, vacuum-formed insulation and a design that eliminates the need for expensive hinges and heavy davits. Burnham Commercial.