How many BTU's does it take to freeze 1 gallon of water?

To freeze 1 gallon of water, it requires approximately 144 BTUs. This is based on the latent heat of fusion, which is the energy needed to change water from liquid to solid at 32°F (0°C). Since 1 gallon of water weighs about 8.34 pounds, the total energy required includes the cooling of the water to its freezing point as well as the phase change.