The British thermal unit (BTU or Btu) is a unit of energy used in the power, steam generation, heating and air conditioning industries. In scientific contexts the BTU has largely been replaced by the SI unit of energy, the joule (J), though it may be used as a measure of agricultural energy production (BTU/kg). It is still used 'unofficially' in metric English-speaking countries (such as Canada, the United Kingdom, and sometimes in New Zealand), and remains the standard unit of classification for air conditioning units manufactured and sold in many non-English-speaking metric countries.
In North America, the term "BTU" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills, and air conditioners. When used as a unit of power, BTU 'per hour' (BTU/h, that is, BTU divided by hour) is understood, though this is often confusingly abbreviated to just "BTU".
Definitions[]
A BTU is defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree from 60° to 61°Fahrenheit at a constant pressure of one atmosphere. As is the case with the calorie, several different definitions of the BTU exist, which are based on different water temperatures and therefore vary by up to 0.5%
Conversions[]
One BTU is approximately:
- 1 054 – 1 060 J (joules)
- 2.931 ×10-4 kWh (kilowatt hours)
- 252 – 253 cal (calories, or "little calories")
- 0.25 kcal (kilocalories, "large calories", or "food calories")
- 25 031 – 25 160 ft·pdl (foot-poundal)
- 778 – 782 ft·lbf (foot-pounds-force)
Other conversions:
- In natural gas, by convention 1 MMBtu (1 million BTU, sometimes written "mmBTU") = 1.054615 GJ. Conversely, 1 gigajoule is equivalent to 26.8 m3 of natural gas at defined temperature and pressure. So, 1 MMBtu = 28.263682 m3 of natural gas at defined temperature and pressure.
- 1 standard cubic foot of natural gas yields ≈ 1030 BTU (between 1010 BTU and 1070 BTU, depending on quality, when burned)
Associated units[]
The BTU per hour (BTU/h) is the unit of power most commonly associated with the BTU. The term is sometimes shortened to BTU hour (BTU.h) but both have the same meaning.
- 1 watt is approximately 3.413 BTU/h
- 1000 BTU/h is approximately 293 W
- 1 horsepower is approximately 2,544 BTU/h
- 1 therm is defined in the United States and European Union as 100,000 BTU—but the U.S. uses the BTU59 °F whilst the EU 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 (1 kW·h, or about 3412 BTU).
See also[]
- Glossary Index
- Conversion of units
- Latent heat
- Metrication
References[]
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