WNS series automatic oil or gas fired boilers are with instant installation and horizontal inner combustion boiler with three strokes, wet backs and fire tubes. The main press components include boiler shell, tube plates, back combustion room, wave hearth, and smoke tube.

 The boiler smoke stroke is of three-stroke designs. The first design is structure of wave hearth and back combustion room to enhance the combustion room flexibility. The second stroke is of screwed smoke tube structure to enhance heat transfer and to improve thermal efficiency. The third stroke is of light smoke tube to improve the smoke exhaust temperature and to prevent acid corrosion caused by low exhaust temperature.