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

BTUs are usually used in defining the heating power of fuels as well as the cooling power of air conditioning systems.

BTU per hour (BTU/h) is the unit of power associated with the BTU and is often converted to kilowatts (kW): 1 kilowatt is approximately equal to 3412 BTU/h. Therefore, with the kW value rounded by convention, we will have that:

- 1.5 kW equals 5000 BTU;
- 2.0 kW equals 7000 BTU;
- 2.5 kW equals 9000 BTU;
- 3.5 kW equals 12000 BTU;
- 4.2 kW equals 15000 BTU;
- 5.0 kW equals 18000 BTU;
- 6.0 kW equals 21000 BTU;
- 7.1 kW equals 24000 BTU;
- 8.0 kW equals 27000 BTU;
- 10.0 kW equals 34000 BTU;
- 12.5 kW equals 42000 BTU;
- 14.0 kW equals 48000 BTU;
- 20.0 kW equals 68000 BTU;
- 25.0 kW equals 84000 BTU.