The MightyTherm series boilers and water heaters are Category I (non-positive vent pressure, non-condensing) natural draft appliances. They are available in a range of gas input rates (from 175 MBH to 5000 MBH) (51.2 kW to 1465 kW) and firing modes (single stage to motorized modulation) to ensure efficient operation (up to 83%) with most building or process heat loads. The MightyTherm series is available for either propane or natural gas fuels.