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.
Therms (UK)
The therm (UK) is a unit of heat energy primarily used in the United Kingdom to measure the energy content of natural gas. It is defined as 100,000 British thermal units (BTUs) which is approximately 105.5 megajoules (MJ).