Editing Horsepower (section)

===Boiler horsepower===
Boiler horsepower is a [[steam boiler|boiler]]'s capacity to deliver [[steam]] to a [[steam engine]] and is not the same unit of power as the 550&nbsp;ft lb/s definition. One boiler horsepower is equal to the thermal energy rate required to evaporate {{convert|34.5|lb}} of fresh water at {{convert|212|°F}} in one hour. In the early days of steam use, the boiler horsepower was roughly comparable to the horsepower of engines fed by the boiler.<ref>{{citation | first=Robert | last=McCain Johnston | title=Elements of Applied Thermodynamics | publisher=Naval Institute Press | date=1992 | isbn=1557502269 | page=503 }}</ref>

The term "boiler horsepower" was originally developed at the [[Philadelphia Centennial Exhibition]] in 1876, where the best steam engines of that period were tested. The average steam consumption of those engines (per output horsepower) was determined to be the evaporation of {{convert|30|lb}} of water per hour, based on feed water at {{convert|100|°F}}, and saturated steam generated at {{cvt|70|psi}}. This original definition is equivalent to a boiler heat output of {{cvt|33,485|Btu/h|kW}}.{{cn|date=January 2025}} A few years later in 1884, the [[American Society of Mechanical Engineers|ASME]] re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 pounds per hour of water "from and at" {{convert|212|F}}. This considerably simplified boiler testing, and provided more accurate comparisons of the boilers at that time. This revised definition is equivalent to a boiler heat output of {{cvt|33,469|Btu/h|kW}}.{{cn|date=January 2025}} Present industrial practice is to define "boiler horsepower" as a boiler thermal output equal to {{cvt|33,475|Btu/h|kW}},{{cn|date=January 2025}} which is very close to the original and revised definitions.

Boiler horsepower is still used to measure boiler output in industrial boiler engineering in the US. Boiler horsepower is abbreviated BHP, which is also used in many places to symbolize brake horsepower.