Hot Water Circulator:

A hot water circulation system / closed-loop system use a dedicated hot water pipe which loops throughout the home beginning and ending at the water heater. With this type of system the temperature of the hot water which is instantly available out of the tap can quite high. The initial cost of these systems is much higher due to the amount of piping needed to complete the dedicated loop in the home.
A hot water circulator, whose primary component is a water pump, is a system that allows for the constant circulation of hot water in the plumbing of a house or other structure.

Benefits of Hot Water Circulator
The key benefit of hot water circulation is the immediate availability of hot water. Many hot water circulators are advertised as water-savers, as they are thought to help minimize the water waste associated with letting a faucet run until it reaches the desired temperature.
Hot water circulation systems generally fall into two categories: open-loop systems and closed-loop systems. Open-loop systems return water to the water heater via the cold-water line; closed-loop systems use a dedicated hot-water line to cycle water back to the water heater.