GU61-40T40 American Water Heaters 40 Gallon Ultra-Low NOx Natural Gas Water Heater6-year limited Tank warranty, 6-year parts warranty for Residential applications.63 Energy FactorIntelligent Control Logic - The internal microprocessor provides enhanced operating parameters and tighter differentials for precise sensing and faster heating response to optimize performanceHigh Energy Factors - • Eco-friendly non-CFC foam insulation, heat traps and specially designed combustion chamber combine to produce a high Energy Factor for maximum savings on operating costsGreen Choice® Gas Burner -Patented eco-friendly burner design reduces NOx emissions by up to 33% and complies with Low-NOx emission requirements of less than 40 ng/JCoregard™ Anode Rod - Our anode rods have a stainless steel core that extends the life of the anode rod allowing superior tank protection far longer than standard anode rodsBlue Diamond® Glass Coating - Provides superior corrosion resistance compared to industry standard glass lining.