The amount of heat exchange in a heating or refrigeration system can be expressed in British Thermal Units (BTU) per hour. This unit of measurement is valid when considering either the amount of thermal energy absorbed in a heating process or the amount of energy rejected in a cooling process. The BTU/Hour measurement of a device is related to the gallons per minute of liquid flow in the device, and the two units of measurement can be derived from one another with some basic arithmetic.
Things You'll Need
BTU/Hour rating of your device
Measure the difference in temperature between the liquid inside and outside of the heat exchanger.
Multiply the difference by 500 if the liquid flowing through the device is water, or by 485 if it is antifreeze.
Determine the BTU/Hour rating of your device. It should be posted either directly on the device or in the owner's manual.
Divide the BTU/Hour rating determined in Step 3 by your result from Step 2 in order to calculate the gallons per minute of flow in your device.