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N°5 – Constant or variable flow boiler room systems training (A to HND level)

As a general rule, when the condensing boiler feeds several heating circuits, on condition that the manufacturer does not impose a minimum through flow, systems are ideally of « variable flow boiler room» type.

Variable flow boiler room – – – – – – – – – – – – – – – – Constant flow boiler

In fact, in “constant flow” type boiler rooms (with a decoupling cylinder), the recirculation of water by the cylinder leads to re-heating of the returns which increases when the 3WV’s close and reduces boiler efficiency.


Symbolize on the system below, a regulating scheme:
– To regulate the temperature of each circuit from an exterior temperature measurement for each circuit.
– To regulate the temperature of boiler production subject to the requirements of the 2 circuits by modulating the burner power.