Circulator Pumps

A circulator moves water around a closed loop rather than lifting it from a source, so it is sized for flow and head loss through the piping, not for pressure. Get the sizing wrong in either direction and the symptoms show up as noise and short-cycling when oversized, or as cold zones at the end of the run when undersized.

Fixed-speed circulators run at one curve and are matched to the loop at installation. Variable-speed and ECM circulators sense pressure differential and throttle themselves, which matters most on systems with zone valves where the flow demand changes as zones open and close — and they draw a fraction of the wattage of a comparable fixed-speed unit.

Cast iron bodies are for closed hydronic loops only; the oxygen in fresh water will corrode them. Any open loop or potable application — domestic hot water recirculation, for instance — needs a stainless steel or bronze body.

Most residential circulators use the standard flange bolt pattern, so replacing one is usually a matter of matching the flange spacing and the electrical supply.