What is the difference between these systems and tankless water heaters?
These systems do not heat the water, they simply take the water that has cooled in the hot water lines and send it back to the water heater instead of letting it go down the drain. Tankless water heaters heat the water just before it is used. They are usually located near the point of use. If the tankless heater is located far away from where you need to use the hot water, then you can save water by installing a point of use pump system.