British Thermal Unit

**Semantic type:** Quantitative Concept

**Definition:** A non-SI unit of energy equal to the amount of heat required to raise the temperature of one pound avoirdupois of air-free water by one degree Fahrenheit at a constant pressure of one atmosphere. The value of the unit depends on the initial temperature of the water and varies in the range of approximately 1.054 - 1.060 joules.

**Synonyms:** - B.T.U. - B.Th.U. - BTU - British thermal unit - British thermal unit - Btu - Btu (usual) - [Btu] - [Btu] - [Btu]