The water delivery system in the house was installed as a large loop. Water supplies each bathroom and all the sinks through a 3/4″ pex pipe that rises through the slab from a protected 4″ pipe shell and returns under the slab to move on to the next outlet. The entire hot water supply is insulated with R-7 pipe insulation. At the furthest bathroom which is in the crawlspace area of the house, the original owner had installed a hot water return pipe so that water could circulate and stay hot in the pipes. We use this return but only run the pump by remote control when we need hot water in the loop.
There are a few commercial systems for returning hot water to the heater before the water turns on. These don’t need the return water loop but can feed the hot water into the cold water pipes.
We use a Skylink remote control system that has a countdown timer which runs the pump for about 15 minutes and then shuts off. The pump itself has an aquastat that shuts itself off when the water reaches 120 degrees and on when the water is at 100 degrees but it only has power to it when the remote control turns it on.