The BTU, or British Thermal Unit, is a unit of energy used mainly in the United States and the United Kingdom but is also spreading in Italy thanks to the spread of air conditioners. In thermotechnics, the thermal power represents the ratio between the amount of heat exchanged and the time in which this exchange took place, specifically the BTU represents the amount of heat necessary to raise the temperature of a pound of water by 1 ° F.

BTUs are usually used in defining the calorific value of fuels as well as the cooling power of room conditioning systems.

The BTU per hour (BTU/h) is the unit of power associated with the BTU and is often converted into kilowatts (kW): 1 kilowatt is approximately equal to 3412 BTU/h.

* The kW value is rounded by convention.