P15 was originally a Grundfos Alpha 15-55. The plumbing between this circulator and storage is almost all 2” copper, presenting a very low head loss. At full fixed speed, the circulator delivered a flow rate of about 10gpm.
P15 was replaced with a Grundfos 15-58FRC. This is a fixed-speed pump,with three switch-selectable speeds. It was installed with the highest speed selected, but connected to a variable-speed control unit that can vary the speed continuously from 0% to 100%. At 100%, the 15-58 has a flow rate nearly the same as the 15-55.