Bradford White Defender Safety System®, 50 Gallon Residential Gas (Natural) Direct Vent Water Heater with Solid Vent Kit. 6-Year Tank Warranty, 42,000 BTU/Hr. The -264 indicates that this SKU comes with an Aluminum Anode Rod. The -475 indicates that this SKU was designed to operate in Altitudes between 2,001 feet and 7,000 feet.