The circulating hot water pump is designed to decrease the amount of water wasted in the home as well as improve the overall energy efficiency of the hot water heater. Aside from the actual pump, a separate set of pipes are connected to the waste water drains of the home via solenoid-powered valves. Specially designed fluid-heat sensors called thermistors are installed in each of the drain mouths, all of which connects back to a central circuit board.
The circulating pump itself is an all-purpose design called a centrifugal pump. It is located at the end of the separate pipelines where they all connect, just prior to leading back into the home's water filtration system. If the home does not have a filtration system, such as with homes that are on city water supplies, a filtration system is installed, which then leads back into the hot water heater.
The pump, and indeed the entire system, works when the thermistor is activated. A strip of semi-conductive ceramic or polymer is suspended in the pathway of the waste water drains for each of the home's taps. A small electrical current passes through it, but does not return to complete the circuit because the strip acts like a resistor, stopping the flow of electricity. When the strip heats up due to hot water passing over it, the electrical resistance dissipates, and the circuit back to the circuit board is closed. When this happens, the circuit board sends an impulse to the solenoid valve corresponding to that particular thermistor, which shunts the water away from the home's exit drains to the circulation pipes. The water flows mostly under its own pressure, but this is helped along by the centrifugal pump. Inside the round cylindrical pump is a turbine which spins. This turbine creates suction, pulling water in through one port and pushing it out through the other. The water is pushed into the filtration system to ensure it is clean enough to be used for the home's needs, and then goes back into the hot water heater until it's called on. Because the hot water heater is not heating water from room temperature, it wastes less electricity.