Evaluation of Residential Recirculation Pumps

Project Summary

SoCalGas ETP has conducted a series of home tests for residential hot water recirculator “comfort systems.” The results show water savings for all products, but gas savings will depend on user’s behavior.  Results should be applicable to electric water heaters, too. DIY home owners may benefit from lessons learned.

In a typical home without recirculating pump, user may have to wait for a long time for the hot water to arrive. One has to drain the warm water slug in the pipe for a few minutes before the temperature rised from warm to hot.  The waiting time and water wasted becomes a problem. Without installing an expensive and dedicated hot water return line, an easy solution is to install a circulator under the sink farthest from the water heater.  This circulator will pull the warm slug and dispose into the cold water line.  Demand control can be done with several options, such as switches with motion detectors, on-off switches, timer, or remote control transmitter.  The test results of five homes are summarized in this report (Link 1 below).  A condensed flyer is also available (Link 2 below).  Comparing energy use before and after the installation, some users may actually experience a higher heating energy bill, since hot water is more abundant and convenient, or, the circulating pump was let run for longer than necessary. The true value is in fast delivery of comfort - hot water.