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The therm (symbol thm) is a non-SI unit of heat energy. It was defined in the United States in 1968 as the energy equivalent of burning 100 cubic feet of natural gas at standard temperature and pressure. In the US gas industry its SI equivalent is defined as exactly 100,000 BTU59°F or 105.4804 megajoules. Public utilities in the U.S. use the therm unit for measuring customer usage of gas and calculating the monthly bills. In the European Union it was defined in 1979 as exactly 100,000 BTUIT or 105.505 585 262 megajoules. The unit was abolished in the United Kingdom in 1999.
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