Definition
A unit of heat energy. One Btu is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
Plain English
A way of measuring how much heat something contains or produces. The bigger the Btu number, the more heat involved.
Context Anchor
Seen in aircraft heating and air-conditioning information, fuel energy discussions, and maintenance data for systems that produce or remove heat.
Derivation
Called 'British' because the unit was developed using the pound and the Fahrenheit scale, both standard in older British measurement. 'Thermal' comes from the Greek therme, meaning heat. So a Btu is literally a 'British heat unit.'
Why Pilots Care
Aviation fuels are often rated by their energy content in Btu per pound. Higher Btu per pound means more energy released when burned, which directly affects engine power and range.
Grounding Statement
If a heater has a higher Btu rating, it can add more heat in a given time than a lower-rated heater.
Intuition Check
A Btu is not a temperature. It is an amount of heat energy that can raise temperature, lower temperature when removed, or be released by fuel.
Example Sentence 1
Aviation gasoline produces roughly 20,000 Btu of heat energy per pound when burned.
Example Sentence 2
Technicians check the air conditioning system's Btu rating during preflight inspections.