Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly, so they can be two to three times more energy efficient than conventional combustion water heaters. The plumbing system is designed so that the main hot water line is routed as closely as possible to all the hot water fixtures. This means that there is little water in the small pipes running from the main line to the fixture so that hot water arrives quickly at every fixture. This water-saving measure is also much more convenient for the occupant.
To save energy, the circulation pump required for the hot water line is fitted with a sensor located immediately after the last fixture so that the pump can shut off once hot water has been circulated. The pump will only resume when the water has decreased in temperature by about 20 degrees. As a result, the recirculation pump might run for two minutes per hour rather than continuously.