Btu (15.6°C)
The Btu (15.6°C) specifically refers to the energy needed to raise the temperature of water from 60°F (15.6°C) to 61°F.
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).