BTU Defined A BTU or British Thermal Unit is the amount of heat applied to raise the temperature of 1 pound of water up 1 more degree Fahrenheit.
Heat output comparative measures in the US are logged as BTUs.
The U.S. Energy Information Administration has a great history an explanation of BTUs here.
Why use British thermal units?
Energy or heat content can be used to compare energy sources or fuels on an equal basis. Fuels can be converted from physical units of measure (such as weight or volume) to a common unit of measurement of the energy or heat content of each fuel. The U.S. Energy Information Administration (EIA) uses conventional Btu as a unit of energy content.
EIA collects data on the physical amounts (volume or weight) of energy sources. For example, the physical volumes o fossil-based fuels consumed in the United States in 2018 and Btu equivalents were
- Petroleum–7.47 billion barrels–36.95 quadrillion Btu
- Natural gas–29.96 trillion cubic feet–30.97 quadrillion Btu
- Coal–687.33 million short tons–13.24 quadrillion Btu