Horsepower (hp)
Horsepower, symbol hp, is a non-SI unit of power introduced in the late 18th century by James Watt. He developed the term to market his steam engines by relating their work to that done by draft horses. One horsepower was standardized as 550 foot-pounds per second, or about 745.7 watts in mechanical terms. Despite not being metric, horsepower remains widely used in the automotive, aviation, and machinery industries, particularly in the United States and the United Kingdom. Its continued popularity is due to tradition and the practicality of relating to horsepower over abstract units, such as watts. Bridging from non-metric to metric units, the megawatt further illustrates the diversity and scope of power measurement in modern contexts.
BTU per hour (BTU/hr)
BTU per hour (BTU/hr) is a power measurement derived from the British Thermal Unit, which represents the heat needed to raise one pound of water by one degree Fahrenheit. One BTU/hr corresponds to about 0.293 watts. This unit has traditionally been used in both the UK and US, especially within the heating, ventilation, and air conditioning (HVAC) sector. It is still widely employed to rate the output of appliances like furnaces and air conditioners. Despite not being part of the metric system, BTU/hr persists in North America due to its deep-rooted presence in industry standards and consumer usage.