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Therm

Therm

This article has been reviewed by the following Topic Editor: Peter Saundry

Definition

The therm (symbol thm) is a non-SI unit of heat energy used to measure the consumption of natural gas. In the U.S., the legal definition (made in 1968) is that the therm equals 105.4804 megajoules. The European Union's definition, made in 1979 using the more current IT Btu, is 105.5060 megajoules.

Gas is metered by volume, often in units of hundreds of cubic feet (CCF), but, since the heating value of natural gas varies with the purity of the product, it is sold by its heating value or heat content. Volume is measured in cubic feet and heat value in Btu's.

To standardize the measurement of natural gas, certain adjustments are made on a typical natural gas bill. The heat content of a cubic foot of gas may contain between 1,000 and 1,060 Btu's. A standard cubic foot is 1,031 Btu's. For purposes of measurement for sale, the actual Btu content is determined and a factor applied to convert to standard cubic feet or to the heat content of standard cubic feet.

History

The names of the unit comes from the Greek word for heat, therme.

Conversions


from / to Joule kilowatt-hour electronvolt calorie Btu horsepower
hour
foot-pound dyne-
centimeter
therm
1 Joule 1 0.278 · 10?3 6.241 · 1018 0.2388 9.4782 · 10?4 3.7251 · 10-7 0.7376 1 · 107 9.4782 · 10?9
1 kilowatt-hour 3.6 · 106 1000 22.5 · 1024 8.5985 · 105 3.4121 · 103 1.3410 2.6552 · 106 3.6 · 1013 0.0341
1 electronvolt 0.1602 · 10?18 44.5 · 10?27 1 3.8267 · 10?20 1.5186 · 10?22 5.9682 · 10?26 1.1817 · 10?19 1.6022 · 10?12 1.5186 · 10?27
1 calorie 4.1868 1.163 · 10?3 0.261 · 1018 1 3.9683 · 10?3 1.56 · 10?6 3.0880 4.186 · 107 3.9683 · 10?8
1 Btu 1.055 · 103 0.293 6.585 · 1021 251.996 1 3.9302 · 10?4 778.169 1.05435 · 1010 1 · 10?5
1 horsepower-hour 2.6845 · 106 745.60 1.6755 · 1025 6.4119 · 105 2.5444 · 103 1 1.98 · 106 2.6845 · 1013 2.5444 · 10-2
1 foot-pound 1.3558 3.7662 · 10-4 8.4623 · 1018 0.3238 1.2851 · 10-3 5.0505 · 10-7 1 1.3558 · 107 1.2851 · 10-8
1 dyne-centimeter 1 · 10-7 2.7778 · 10-11 6.2415 · 1011 2.4 · 10-8 9.4782 · 10-11 3.7251 · 10-14 7.4 · 10-8 1 9.4782 · 10-16
1 therm 1.0551 · 108 2.9307 · 104 6.5851 · 1026 2.520 · 107 1 · 105 39.301 7.7817 · 107 1.0551 · 1015 1


Further reading

Citation

Cutler J. Cleveland (Lead Author);Peter Saundry (Topic Editor) "Therm". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth December 12, 2006; Last revised Date December 12, 2006; Retrieved June 19, 2013 <http://www.eoearth.org/article/Therm>

The Author

Cutler J. Cleveland Cutler J. Cleveland  is Professor of Earth and Environment at Boston University, where he also is on the faculty of the Center for Energy and Environmental Studies. Professor Cleveland is Editor-in-Chief of the Encyclopedia of Energy (Elsevier, 2004), winner of an American Library Association award, the Dictionary of Energy (Elsevier, 2005), Handbook of Energy (Elsevier, forthcoming), and is the Founding Editor-in-Chief of the Encyclopedia of Earth.  He is the recipient of the Adelma ... (Full Bio)

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