A heating circuit refers to the piping system that carries hot water from the boiler to radiators or underfloor heating and back. This is also commonly called a heating zone. Heating circuits are used to improve the efficiency of heating systems.
By splitting a heating system into multiple circuits, heat can be distributed separately for different areas of a house. This means that heating can be turned down in any one area when it is not needed.
Furthermore, different flow temperatures can be achieved on each separate heating circuit. This can be an advantage when both radiators and underfloor heating are used in one house. As radiators require higher flow temperatures than underfloor heating systems, they can be controlled using separate heating circuits with different flow temperatures.