A recirculating pump works with conventional water heater basically like this. There is a small pump that is place near the water heater along with a check valve. You have to have a return line connected to the hot water supply line close to the furthest point in the house. The return line connects to the pump and then into the water heater. Hot water is circulated through the system as long as the pump is operating. Some pumps have a timer so that it only operates during the times hot water is normally used, others, like mine, operate 24/7. There is no wasted water or time waiting for cold water to purge from the hot water line, so you have truly instant hot water. I use a Lange brand pump, but there are other brands out there.