Bradford White 100 Gallon Commercial Gas (Natural) Atmospheric Vent Water Heater with Flue Damper and Electronic Ignition. 3-Year Tank Warranty, 199,999 BTU/Hr., 120 Volts, Single Phase, with Power Cord included. The -823 indicates that this SKU was designed to operate in Altitudes between 2,001 feet and 5,000 feet.