A Flowmeter measures the actual flow of water through your recirculation system. These meters are calibrated to the size of your piping - e.g. if you have 1 1/2 pipng you would purchace a 1 1/2 inch Flowmeter; for 2" piping, a 2 inch Flowmeter etc. This 1 1/2" Flowmeter will measure between 20-75 Gallons Per Minute (GPM). This guide shows you how to install a Flowmeter on the discharge side of a 1 1/2" pipe system.