A circulation pump is a type of pump used to circulate gases, liquids, or slurries in a closed off pipeline. Circulation pumps are usually found circulating water in heating or cooling systems. Because these pumps only circulate liquid in a closed circuit, they only need to overcome the friction of a piping system (compared to lifting a liquid from a lower point to a higher point).
Circulation pumps are usually electrically powered centrifugal pumps. In homes, they are often small, sealed, and rated a fraction of a horsepower, but in commercial usage they can range up to many horsepower and the electric motor is usually kept apart from the pump body by some form of coupling. The sealed units used in home applications often have the motor rotor, pump impeller, and support bearings combined and sealed within the water circuit. This avoids one of the principal challenges faced by the larger, two-part pumps: maintaining a water-tight seal at the point where the pump drive shaft enters the pump body.
Small- to medium-sized circulator pumps are usually supported entirely by the pipe flanges that join them to the rest of the hydronic plumbing. Large pumps are usually pad-mounted.
Pumps that are used solely for closed hydronic systems can be made with cast iron components as the water in the loop will either become de-oxygenated or be treated with chemicals to inhibit corrosion. But pumps that have a steady stream of oxygenated, potable water flowing through them must be made of more expensive materials such as bronze.
Circulating pumps are often used to circulate domestic hot water so that a faucet will provide hot water instantly upon demand, local water authorities offer rebates to homeowners and builders that install a circulator pump to save water.