Btu (15°C)
The Btu (15°C) is a specific variant of Btu to reflect the energy needed to raise the temperature of water at 15 degrees Celsius by one degree.
Btu (mean)
Btu (mean) is a unit of energy used primarily in the United States defined as the heat required to raise the temperature of one pound of water from 59°F to 60°F under standard atmospheric pressure.