Bradford White Defender Safety System®, 50 Gallon Tall Residential Gas (Liquid Propane) Atmospheric Vent Water Heater. 6-Year Tank Warranty, 38,000 BTU/Hr. The "-394" indicates that this SKU comes with a Top T&P Location. The "-475" indicates that this SKU was designed to operate in Altitudes between 2,001 feet and 7,000 feet. The "-500" indicates that this SKU comes with White Rodgers Mechanical Control.