... High anti-corrosion tank 4.OEM available Rooftop Unpressurized Solar Water Heater with Vacuum Tubes High anticorrosion tank: SUS304 food grade stainless ... steel, cleaner water as a result of cleaner inner water tank; advanced freewelding technique, no welds ... wind, stronger bearing ability, higher stability. Rooftop Unpressurized Solar Water Heater with Vacuum Tubes