Definition for word: Therm

 A unit of heat equal to 100,000 British thermal units (Btus); commonly used for natural gas.

Referrence from

The therm (symbol thm) is a non-SI unit of heat energy equal to 100,000 British thermal units (BTU). It is approximately the energy equivalent of burning 100 cubic feet (often referred to as 1 Ccf) of natural gas.

Since meters measure volume and not energy content, a therm factor is used by gas companies to convert the volume of gas used to its heat equivalent, and thus calculate the actual energy use. The therm factor is usually in the units therms/Ccf. It will vary with the mix of hydrocarbons in the natural gas. Natural gas with a higher than average concentration of ethane, propane or butane will have a higher therm factor. Impurities, such as carbon dioxide or nitrogen, lower the therm factor.

The volume of the gas is calculated as if measured at standard temperature and pressure (STP). The heat content of natural gas is solely dependent on the composition of the gas, and is independent of temperature and pressure.

The therm is equal to about 25,200 kilocalories or about 29.3 kilowatt hours of electrical energy. One therm can also be provided by about 96.7 cubic feet of natural gas. The therm sometimes has been confused with the thermie (see below). The names of both units come from the Greek word for heat.

A thermie (th) is a metric unit of heat energy, part of the meter-tonne-second system sometimes used by European engineers. The thermie is equal to the amount of energy required to raise the temperature of 1 tonne of water by 1°C. The thermie is equivalent to 1,000 kilocalories, 4.1868 megajoules or 3968.3 Btu.

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