Short for British thermal unit, an British standard unit of energy. One Btu is equal to the amount of heat required to raise the temperature of one pound of liquid water by 1 degree Fahrenheit at its maximum density, which occurs at a temperature of 39.1 degrees Fahrenheit. One Btu is equal to approximately 251.9 calories or 1055 joules.
The heat output of computer devices is often expressed in Btus.
