Heat pumps can operate with microbore pipework, but there are limitations. Because heat pumps run at lower flow temperatures (35–55 °C versus 70–82 °C for boilers), they require higher flow rates to deliver the same heat output. In microbore systems, this increases resistance and can reduce efficiency.
Where possible, replacing microbore with larger pipework is the best option, improving efficiency, lowering running costs, and enhancing reliability. If replacement isn’t feasible, careful hydraulic design is essential—flow rates should generally remain below 1 m/s and pressure drops below 350 Pa/m.
When retaining microbore pipework, the system should be designed to mirror original operating conditions. This may involve slightly higher flow temperatures or a wider temperature differential (ΔT) to limit flow rates. If necessary, hydraulic separation (e.g. a low-loss header) can allow the heat pump to run at low resistance while a secondary pump serves the microbore circuit.
Installers should note:
-
Balancing is crucial for even radiator performance.
-
Flushing prevents blockages.
-
Larger or additional emitters may be required at lower flow temperatures.
A hybrid system is another option, using the boiler to provide higher-temperature water in colder weather, keeping the heat pump within its optimal efficiency range.
Back to FAQs