The Bosch Therm 520HN and the Bosch Therm 520PN can be installed at elevations for people with homes or cabins in Colorado, New Mexico, etc. The Bosch 520HN & 520PN are natural drafting units and require a 6" galvanized type B-vent and must vent vertical for a minimum of 6' to the rain cap for all elevations over 2,000'.
Gas pressure is dependent upon the gas type whether it is Natural Gas (NG) or Liquid Propane (LPG) and also the length of the gas line. See sizing charts in the installation manual for the heaters. The Bosch 520HN & 520PN can be installed above 4,500' elevation but the unit would have to have the gas pressure adjusted using a manometer to compensate for the air and gas mix at the high elevation. Please see the insert below for more details.
Cutting the gas pressure back as per the chart above is called "de-rating" the burner. Elevations above 2,000 ft require the Bosch tankless water heater to be de-rated 4% for every 1,000 feet. Basically you will loose 4% of your heating capacity for every 1,000 ft.
