The British thermal unit (BTU or Btu) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit (Physical analogue: one four inch wooden kitchen match consumed completely generates 1 BTU). In science, the joule, the SI unit of energy, has largely replaced the BTU.
The BTU/h is most often used as a measure of power in the power, steam generation, heating, and air conditioning industries, and also as a measure of agricultural energy production (BTU/kg).[verification needed] It is still used in metric English-speaking countries (such as Canada), 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 heat value (energy content) of fuels is expressed in BTUs.