Btu

Part of speech: noun

Definitions

1. A unit measuring the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit ; a standard scale for quantifying thermal energy transfer in heating and cooling systems ; a measure used to evaluate the energy output or consumption of appliances and fuel sources
2. A thermal measurement unit representing the heat needed to increase one pound of water's temperature by one degree Fahrenheit ; commonly used to gauge the energy content of fuels and the capacity of heating and cooling devices ; a standard metric for heat energy used in energy efficiency ratings
3. An energy unit defined by the heat needed to raise one pound of water one degree Fahrenheit ; extensively applied to quantify the power of heating and air conditioning systems ; a conventional measurement for expressing thermal output or fuel energy content

Etymology: BTU stands for "British thermal unit," a unit of heat energy. The name is a plain description rather than a coined term: "British" because the unit was used in the British imperial system, and "thermal" from Greek "thermē," meaning heat, the same root that gives "thermometer" and "thermos." A British thermal unit is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. The lowercase "btu" is simply the same abbreviation written without capitals, which is common for unit symbols in informal writing. Because the unit belongs to the imperial system, it remains most familiar in the United States, where it is used for heating, cooling and fuel ratings, while much of the rest of the world measures energy in joules.