Btu (15.8°C, ISO)
The British Thermal Unit (Btu) is a traditional unit of heat, defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. The Btu (15.8°C, ISO) is a specific variant standardized by the International Organization for Standardization (ISO) based on the calorie defined at 15.8°C.
Therm (EC)
The therm (EC) is 100,000 Btu (International Table), or about 105.5 megajoules (MJ). Gas in the United Kingdom was historically billed in therms, and the EC stands for European Community, to tell it apart from the US therm.