Bryan Indirect Water Heaters are now available in sizes to 8,000,000 Btu/hr with water heating capacities to 7,680 gallons per hour at 100-deg. temperature rise (40 deg. to 140 deg. F). The additional larger sizes broaden their range of use for multi-purpose heating applications. With the indirect heat exchanger method, the primary water in the heater is maintained at a constant temperature and recirculated only within the heating vessel. The heat exchanger, placed in the primary water, absorbs heat and transfers it to the water flowing through its copper tubes. Bryan Steam LLC.