Btu
The British Thermal Unit (Btu) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is primarily used in the United States to describe the energy content of fuels and the power of heating and cooling systems.
Joules
The joule (J) is the SI unit of energy. It is named after the English physicist James Prescott Joule. It is the amount of work done when a force of one newton moves an object by one meter in the direction of the force also known as a newton-meter.