Do Recirculation Pumps Save Energy?
At two field test sites, we installed different types of recirculation pumps along with a return line back to the tank inlet. The pumps used slightly different control methods to keep the main supply trunk primed with hot water to reduce wait times and hot water waste. At both sites the pumps reduced hot water waste but had an even greater impact on standby losses. Hot water waste was reduced by about 4 gallons per day at Site 1 due to pump operation, but standby losses were increased by more than the savings from eliminating this waste. At Site 1 we calculated a net increase in energy use of 1 kWh per day. Recirculating water clearly increases thermal losses from the supply and return piping near the tank; so while water use is lower, energy use increases. Therefore, in regions like the Northeast where energy savings are of more concern than water conservation, recirculation pumps do not seem to be justified.