How to Size a Circulator Pump

Selecting the right circulator pump may be the most important step in designing a hydronic heating system. Unnecessarily large pumps can cause velocity noise, while pumps that are too small may not allow proper heat transmission. Unfortunately, sizing a circulator is not as easy as many people assume. A circulator must be able to handle the flow rate (GPM) and head pressure of the area that it controls. GPM measures the number of gallons that pass a given point in the distribution piping in one minute. Head pressure is a slightly more complicated calculation that has more to do with friction in the pipes than it does with the height of the pipes. There is an inverse relationship between GPM and head pressure (as can be seen on the “pump curve” for each circulator). With increasing head pressure, circulators can handle fewer GPM (and vice versa).

Taco provides a guide that describes how to calculate these figures and select the right circulator for every job. It includes the pump curves for all their 00-Series circulators, which can handle a wide variety of applications. PexSupply.com carries circulator pumps from Taco, Grundfos, Bell & Gossett, and Wilo.