The Engineering Toolbox explains that 34.5 boiler horse power is equal to 1 pound per hour of steam. One boiler horse power is equal to 33,475 British Thermal Units per hour. Therefore, to convert BTU per hour to boiler horse power, divide the BTU per hour by 33,475. To convert the boiler horse power to pounds per hour of steam, multiply by 34.5.

The BTU measures the amount of energy needed to increase the temperature of 1 pound of water by 1 degree Fahrenheit. The Engineering Toolbox explains that BTU per hour, boiler horsepower and pounds of steam per hour can all be used to express the capacity of a boiler.

BTU per hour can also be converted into various units to describe the energy content of different types of fuels, such as cubic feet of natural gas or gallons of kerosene. The conversion processes are complicated and vary by the type of fuel used. Since all of these varied units are expressing the same concept, the amount of energy, modern science has tried to abandon these varied units and replace them with one measure of energy: the joule. One BTU is equivalent to 1054 joules. Many industries resist the joule and continue to use their preferred units of energy measurement.