A. O. Smith's Signature 100 Series 40-Gallon Tall Low NOx Atmospheric Vent Natural Gas Water Heater is designed to provide efficient and reliable hot water for households with 3 to 4 people when sized appropriately. With an environmentally friendly 35,500 BTU Low NOx gas burner, this model delivers 65 gallons of hot water in the first hour. It features an electronic gas valve that provides precise temperature control for optimum hot water delivery without the need for an external power source. For your convenience, the gas valve also includes an LED status indicator for diagnostics reporting and a push button ignition to simplify the startup process. A. O. Smith’s 40-gallon model is designed with your safety in mind. With a built-in safety system, this model reduces the risk of accidental flammable vapor ignitions. A factory-installed temperature and pressure relief valve and tamper-proof drain valve also ensures safe operation. This model is built to last. It features a protective anode rod and a ceramic fused tank shield designed to reduce corrosion and provide ultimate tank protection. It also features a self-cleaning dip tube designed to reduce sediment build-up and extend the overall life of the water heater. This added protection comes with a 6-year limited warranty to give you additional peace of mind.