BTUs

BTU stands for British Thermal Unit, a traditional unit of energy used mainly in heating and cooling industries in the United States and Canada. By definition, one BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at standard pressure. In practical terms, one BTU is approximately 1,055 joules.

BTU is also used as a rate of heat transfer, written as BTU per hour (BTU/h). This power rating is common for furnaces, air conditioners, and heat pumps. Related HVAC units include the ton of refrigeration, equal to 12,000 BTU/h, and the MBH, or thousand BTU per hour. For electrical energy, 1 kilowatt-hour is about 3,412 BTU.

BTUs are widely used to describe the energy content of fuels. Natural gas and propane are often quoted in BTU per unit volume or mass, such as BTU per cubic foot for gas. Gasoline and heating oils are also expressed in BTUs per gallon.

There are two closely related definitions of BTU—IT (international table) BTU and thermochemical BTU. The values are very close and are often treated interchangeably in everyday HVAC work, yielding approximately 1,055 joules per BTU. Other related units include the therm (100,000 BTU) and the MBH (1,000 BTU/h).