Convert power units between units, using exact SI factors.
One metric horsepower is 0.7355 kilowatts, so a 150 hp engine is about 110 kilowatts. The watt is the SI unit of power in the BIPM brochure and means one joule per second. A Latvian registration document states power in kilowatts, not horsepower.
Power is the rate at which energy is used; energy is the total amount. In SI units one watt is one joule per second, so power times time gives energy. An electricity bill charges for energy in kilowatt-hours, not for an appliance's power in kilowatts.
They are two separate historical standards: metric horsepower is 735.5 watts, imperial horsepower 745.7 watts — 1.4% more. Neither is an SI unit and neither appears in the BIPM brochure, which is why official documents state power in kilowatts.
BTU per hour is power, not energy: 12,000 BTU per hour is about 3.5 kilowatts in SI units. The figure states how much heat the unit can move in an hour. For a room, about 100 watts per square metre is the usual rule at standard ceiling height.