Rheem 42VR50-40F High Efficiency Natural Gas Water Heater, 50 Gallon,Rheem,42VR5040F" /> One-of-a-kind air/fuel shut-off device offers double protection Maintenance free  no filter to clean Low NOx design for low nitrous oxide emissions EverKleen patented system fights sediment build-up, reduces fuel costs, and provides more hot water Certified for applications up to 6,000 feet above sea level