British thermal unit

noun

: the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a specified temperature (such as 39°F)

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Despite its name, the British thermal unit, or BTU, may be more widely used in North America than in Britain. Air conditioners, furnaces, and stoves are generally rated by BTUs. (Though "BTUs" is often short for "BTUs per hour;" in air-conditioner ratings, for instance, "BTUs" really means "BTUs of cooling capacity per hour".) Fuels such as natural gas and propane are also compared using BTUs. The BTU first appeared in 1865 and isn't part of the metric system—the metric unit of energy is the much smaller joule—so it isn't much used by scientists, but its practicality keeps it popular for consumer goods and fuels. A better-known heat unit is the calorie; a BTU is equal to about 252 calories. (Since the familiar food calorie is actually a kilocalorie, a BTU equals only about a quarter of a food calorie.)

Examples of British thermal unit in a Sentence

Recent Examples on the Web

These are best for large areas or for placing in a central spot and heating multiple rooms. BTUs BTUs are British thermal units or the amount of energy required to raise one pound of water one degree Fahrenheit. —John Sass, Field & Stream, 3 Aug. 2023

That’s because a barrel of oil contains 5.8 million British thermal units’ worth of energy. —Bill McKibben, The New Yorker, 5 July 2023

At the Waha trading hub in West Texas, spot prices Wednesday hit $2.36 per million British thermal units, 54% more than the daily average over the previous three months. —David Uberti, WSJ, 23 June 2023

Using radiant infrared heat, this Duraflame pumps out some serious Btu (British thermal units). —Gabriel Morgan, Better Homes & Gardens, 9 June 2023

Natural-gas futures shed 6.7% to close at $2.011 per million British thermal units after weekly inventory data showed a small withdrawal from storage. —Ryan Dezember, WSJ, 6 Apr. 2023

Cost of a British thermal unit on the futures market hovered at just over $2 on Tuesday — down from $9.65 last August. —Ron Hurtibise, Sun Sentinel, 4 Apr. 2023

Front-month futures for Henry Hub U.S. benchmark natural gas fell 4.1% on Thursday to $2.09 per million British thermal units, the lowest since 2020. —Jinjoo Lee, WSJ, 30 Mar. 2023

That’s a ratio of cooling capacity, measured in British thermal units per hour (Btu/h), to the power input in watts (W). —Justine Calma, The Verge, 24 Mar. 2023

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Word History

First Known Use

1865, in the meaning defined above

Kids Definition

British thermal unit

noun

: the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a specified temperature (as 39°F or 60°F) and equal to about 1055 joules

—called also Btu

Medical Definition

British thermal unit

noun

: the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a specified temperature (as 39°F)

—abbreviation Btu