The British thermal unit reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

British thermal unit

The British thermal unit (Btu, BTU) is a nonmetric unit of energy, used in the United States and, to a certain extent, the UK. The SI unit is the joule (J), which is used by most other countries. 1 Btu is defined by the amount of heat required to raise the temperature of one pound avoirdupois of water from 63 °F to 64 °F. It is often used to describe the heat value of fuels and heating and cooling system capacities.

1 Btu is approximately:

252 calories,

778 ft.·lbf.,

1,055 joules

A unit called the quad is defined as 10¹⁵ BTUs, which is about 1.055 × 10¹⁸ joules, and the therm is defined in the United States and European Union as 100,000 BTU.

The Btu should not be confused with the Board of Trade Unit (B.O.T.U.), which is a much larger quantity of energy.

See also: conversion of units, metrication

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