Btu (3.9°C)
The Btu (3.9°C) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at the temperature where water reaches its maximum density which occurs at approximately 3.9°C (39°F).
Therm (US)
The Therm (US) is a unit of heat energy commonly used in the United States, particularly in the context of natural gas consumption. It is the amount of energy equivalent to burning 100 cubic feet of natural gas and is equivalent to about 105,480,400 joules.