Mighty Therm, Cupronickel Tube Assembly, Indoor Boiler (8 Tubes), 850, Laars Code Compliant ASME Tube Assemblies, Built in accordance w/the requirements of the ASME Boiler and Pressure Vessel Code, Cupronickel tubes w/glass-lined tubs, ideal for corrosive or softwater applications (under 7.5 grains hardness), or when hard water pumping creates higher tube velocities. Suitable for use w/swimming pool heaters.