BTU is short for British Thermal Units.
BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
Formula to calculate BTU.
The flow rate is measured in gallons per minute.
Suppose the rate of flow of water i your household is 6 GPM, calculate the BTU if the leaving process temperature is 27 degree Fahrenheit and the entering process temperature is 25 degree Fahrenheit.
Therefore, your BTU is 6,004.8.