Hayward H400FDNASME Universal H-Series Low NOx 400,000 BTU Natural Gas Commercial Pool and Spa Heater Standard Cupro nickel heat exchanger for superior value and reliability Polymer and low lead bronze (commercial ASME) header for excellent corrosion resistance Hayward Universal design for easy and versatile professional installation Environmentally responsible low NOx emissions to meet or exceed air quality emission standards in all Low NOx regions