Secondary circuit

A secondary circuit is a heating-water circuit that carries heat from a primary heat-source circuit towards radiators, underfloor heating, fan coils or other heat emitters. In heat pump and boiler schematics it is often the load side of a low-loss header, buffer tank, plate heat exchanger or closely spaced connection, with its own pump, valves and controls. CIBSE (Chartered Institution of Building Services Engineers) Journal, Hamworthy and FlexEJ describe low-loss headers as separating primary and secondary circuits so pumps can operate with less interaction. The term is not an electrical circuit, a separate heat pump, a heat loss calculation or proof that the system is correctly designed.