Btu (I.T.)
The British thermal unit (International Table), Btu (IT), is about 1,055 joules, roughly the energy needed to warm one pound of water by one degree Fahrenheit. In the United States air conditioners and furnaces are rated in Btu per hour.
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.