The ProLine XE® 40-Gallon Ultra-Low NOx Direct Vent Natural Gas Water Heater offer horizontal or vertical venting options in an FVIR solution to reduce the risk of accidental fires involving flammable vapors.Featuring a 40-gallon (nominal) tank and a 36,000 BTU gas burner, the GDVNL-40L-100 Direct Vent Ultra-Low NOx delivers a first hour rating of 64 gallons and a recovery rate of 39 gallons per hour. It carries a 6-year limited tank 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® 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.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.