Water circulation pumps recirculate round a closed system; a system that operates in a loop where the liquid being transferred never comes into contact with atmospheric pressure. For this reason, they are sometimes referred to as a closed loop circulating pump.
Common applications where a circulating water pump is used include cooling systems, water heaters, swimming pools, HVAC and boilers. Due to their ability to handle water efficiently at reasonable flow rates and pressures, recirculating water pumps are usually of centrifugal design. Although this is not always the case, close loop circulating systems are often continuously operated for example in boiler or engine cooling. For these applications, large, heavy duty water recirculation pumps are required to bear the strain.