Btu (I.T., pre-1956)
The Btu (I.T., pre-1956) refers to the International Table Btu, a specific definition used before 1956. It represents the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at a constant pressure of one atmosphere.
Therm (EC)
The Therm (EC) is a unit of energy primarily used in the United Kingdom for billing purposes in the gas industry. It is defined as 105.5 megajoules (MJ). The "EC" in Therm (EC) stands for European Community as it was created to standardize within European countries.