A circulator pump is a specific type of pump used to circulate liquids, gases or slurries in a closed circuit. A common use is in hydronic HVAC systems (defined as those which use water as the heat exchange medium), circulating hot or chilled water for heating or cooling. 

Circulator pumps used in hydronic systems are usually centrifugal, driven by an integral electric motor. Alternatively, the motor may be mounted externally to the pump body, with a mechanical coupling. 

In HVAC systems, variable speed circulator pumps can help to reduce overall system energy consumption when compared to fixed speed circulators. As variable volume hydronic systems have become more common, there has been a tendency to use inverter-control for the circulator motors. This enables rapid response to system changes.