GU81-50T40R American Water Heaters ProLine Master 50 Gallon Ultra-Low NOx Natural Gas Water Heater With their innovative design and commercial-grade components, our ProLine® Master gas water heaters are built for strong, long-lasting performance.8-year limited Tank warranty, 8-year parts warranty for Residential applicationsIntelligent Control Logic-The internal microprocessor provides enhanced operating parameters and tighter differentials for precise sensing and faster heating response to optimize performance.Green 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/J.Coregard™ 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 rods.Blue Diamond® Glass Coating - Provides superior corrosion resistance compared to industry standard glass lining.Ultra-Low NOx complies with requirements in California of less than 10 ng/J NOx Emissions