Btu
One BTU is the energy required to heat 1 avoirdupois pound of liquid water by 1 degree Fahrenheit, at a pressure of one atmosphere.
One BTU is the energy required to heat 1 avoirdupois pound of liquid water by 1 degree Fahrenheit, at a pressure of one atmosphere.
The National Bureau of Standards (NBS, now known as The National Institute of Standards and Technology) defined the cal15 as being the ammount of energy needed to warm 1g of water from 14.5°C to 15.5°C