Determine the heat to transfer, choose the design ΔT, calculate required flow, size the pipework, check velocity, calculate pressure drop, check available pump head, check minimum flow in every operating condition, check permanently available system volume, then commission and verify. Pipe diameter should be an output from the hydraulic design, not the starting assumption.

Higher heat output, or a smaller flow/return temperature difference, means more water flow is required. That flow requirement is what the pipework then needs to support.

A system designed around a 5°C ΔT needs roughly twice the flow of a 10°C ΔT system delivering the same kW. It is an important part of the hydraulic design rather than simply a temperature reading.

28 mm is a pipe size, not a heat-pump design method. The correct size should come from the hydraulic calculation — required flow, internal bore, material, length, fittings, velocity and pressure drop.

Pump performance is a curve, not a promise. The real question is not whether a single pipe diameter can carry the flow, but whether the complete circuit can deliver that flow within the available pump head. A proper design considers the whole system.

Yes, in some systems. Microbore should not automatically be condemned — it should be assessed circuit by circuit, based on branch length, room load and required flow.

You can have plenty of water volume but inadequate flow, or excellent flow but insufficient volume. A buffer tank does not automatically fix a flow-rate problem. This is why the design should consider permanently available system volume, particularly where extensive zoning exists.

No. A buffer tank should solve a defined design problem — insufficient volume, variable flow, hydraulic separation, cycling mitigation, or defrost support. What problem is this buffer solving? If the answer cannot be clearly explained, question the need for it. Buffer tanks can also introduce additional heat loss, pipework, pumps and complexity.

Room heat loss → emitter output → required circuit flow → pipework and hydraulic requirement. Radiator design and pipework design should not be carried out independently. Pipe insulation and the correct system fluid (e.g. glycol) also matter to the design.

A hydraulic design predicts how the system should work. Commissioning confirms whether it actually does — measuring actual flow, temperatures, ΔT and behaviour with different zones open and closed.

Microbore Pipework and Heat Pumps

Radiators & Heat Emitters

Flow Temperature & Controls