BRITISH THERMAL UNIT (BTU)

A unit of heat energy equal to the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. More precisely, the quantity of heat required to raise the temperature of one pound of water from 60F to 61F at a constant pressure of one atmosphere. Also, the quantity of heat equal to 1/180 of the heat required to raise the temperature of one pound of water from 32F (its freezing point) to 212F (its boiling point) at a constant pressure of one atmosphere. The British Thermal Unit is used when the measurement is in degrees Fahrenheit (F) on the Fahrenheit Scale and the Calorie is used when temperature is measured in degrees Celsius (C) on the Centigrade Scale.