The British thermal unit (BTU) is a non-metric 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. A BTU is defined as the amount of heat required to raise the temperature of one pound avoirdupois of water by one degree Fahrenheit; specifying the temperature range over which this happens leads to a number of slightly different BTU values, varying over a range of about 0.5%:
Uses the calorie value of water at its maximum density (39.1–39.2°F)
Uses a calorie averaged over the 32°F to 212°F range
The most widespread BTU, uses the International [Steam] Table (IT) calorie, itself defined for water at 14.5°C (58.1°F) by the Fifth International Conference on the Properties of Steam , held in London in July 1956.
Chiefly American. Uses the 15°C calorie, itself defined as exactly 4185.5 J (Comité international 1950; PV, 1950, 22, 79-80)
A unit called the quad (short for quadrillion) 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 – but the U.S. uses the BTU59°F whilst the E.C. uses the BTUIT.
The BTU should not be confused with the Board of Trade Unit (B.O.T.U.), which is a much larger quantity of energy.
The British thermal unit (BTU or Btu) is a non-metric unit of energy, used in the United States and, to a lesser extent, the UK (where it is generally only used for heating systems).
A BTU is defined as the amount of heat required to raise the temperature of one pound avoirdupois of water by one degree Fahrenheit; specifying the temperature range over which this happens leads to a number of slightly different BTU values, varying over a range of about 0.5%:
The BTU is often used to describe the heat value of fuels, or the heating and cooling power of a system (such as a barbecue grill).
One Btu is the amount of heat needed to raise the temperature of one pound of water 1°F. To get a rough idea of how much heat energy this is, the heat given off by burning one wooden kitchen match is approximately one Btu.
Specifically, one BTU is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.
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