The ProLine® XE 40-Gallon Ultra-Low Nox Atmospheric Vent Natural Gas Water Heater offers highly optimized performance and increased efficiency thanks its automatic flue damper and electronic gas control. The automatic flue damper increases efficiency as it automatically opens and closes to reduce heat loss in standby mode. The intelligent control logic provides enhanced operating parameters and tighter differentials for precise sensing and faster heating response to optimize performance. Featuring a 40-gallon (nominal) tank and a 40,000 BTU gas burner, the GUF-40 standard vent delivers a first hour rating of 68 gallons and a recovery rate of 42 gallons per hour. With a 0.65 Uniform Energy Factor, this model carries a 6-year limited warranty, and meets Ultra-Low NOx emission requirements. Environmentally-friendly insulation and factory-installed heat trap nipples reduce heat loss for maximum energy savings. This ProLine® XE water heater is designed with A. O. Smith's superior commercial-grade tank protection. Advanced tank features include stainless steel CoreGard™ anode rod, Blue Diamond® glass lining and DynaClean™ automatic sediment-cleaning system, all designed to help protect the tank from the corrosive effects of water and extend the life of the water heater. All of these features are accompanied by a 6-year limited tank warranty. A. O. Smith’s ProLine® water heaters are residential products built to commercial-grade standards and are only available for purchase through professional wholesalers and contractors.