Why ASHP Pipework Matters
Heat pumps are flow-rate sensitive. If the primary flow and return pipework is undersized, too restrictive, poorly insulated or over-fitted, the system can struggle to deliver the required heat transfer.
The pipework is not a minor accessory. It affects:
- pump duty
- flow rate
- pressure drop
- heat loss
- installation time
- external routing
- long-term reliability
How To Choose The Pipe Size
Start with the heat-pump manufacturer's required design flow and available external pump head. Heat output alone does not establish a pipe size. Include the complete flow-and-return route, fittings, valves, strainers, heat exchangers and the specified fluid.
Compare candidate Ridgeline sizes using their own pressure-loss data. R-32 HP is designed for heat-pump primary pipework, but it is not an automatic selection for every heat pump or route. A larger size may be needed on a longer or more restrictive circuit.
Use the heat-pump pressure-loss calculator to compare the route, then check the complete result against the chosen heat pump's instructions.
Published Tube-Loss Reference
These selected values come from the Ridgeline + P1 datasheet, Rev 2, July 2026, page 4. They are published manufacturer tube data, not an independent route test or a complete system calculation.
Use the exact tube column. At 20 L/min, the published R-32 HP value is 373 Pa/m and the R-35 value is 128 Pa/m. Substituting the R-35 column would understate R-32 HP tube loss. R-28 is shown for reference comparison, not as a heat-pump size recommendation.
The source table does not state the fluid, temperature or test/calculation conditions alongside these values. Confirm applicability with the technical team before using them for design, particularly for glycol. Include fittings, bends and other components separately. No interpolation or extrapolation is supplied here.
| Flow, L/min | R-28 | R-32 HP | R-35 |
|---|---|---|---|
| 10 | 225 / 0.40 | 95 / 0.29 | 33 / 0.19 |
| 15 | 500 / 0.60 | 211 / 0.44 | 73 / 0.29 |
| 20 | 885 / 0.80 | 373 / 0.58 | 128 / 0.39 |
| 25 | 1,378 / 1.00 | 580 / 0.73 | 199 / 0.49 |
| 30 | 1,981 / 1.20 | 833 / 0.87 | 285 / 0.58 |
Download the reference data (JSON). The same source file supplies this table and includes its units, PDF revision, source page and scope.
Using and citing this reference
This is a selected manufacturer-data reference, published by Ridgeline Tubes Limited on 27 September 2026. Reference version 1.0. The source remains the P1 Technical Data Sheet, Rev 2, July 2026, page 4.
Keep the source revision, units and applicability note with any project record. Confirm the fluid, temperature and test or calculation conditions before design use. The table excludes fittings, valves, equipment and other circuit losses.
Reference: Ridgeline Tubes Limited. Ridgeline P1 selected tube pressure-loss reference, version 1.0 (2026-09-27). Permanent link to this reference.
For the rest of the project record, use the route comparison worksheet and current approval documents.
Worked Route Example: A 12 m Flow And Return
This example shows how to prepare the route inputs; it does not prescribe a pipe size or claim a tested performance result.
Assume the measured route from the outdoor unit to the plant room is 12 m, and the return follows a separate 12 m run. The circulating water travels through 24 m of tube in total. If a calculator asks for total circuit length, enter 24 m. If it asks for one-way length and explicitly doubles it, enter 12 m. Do not count the return twice.
| Input | What to enter or check |
|---|---|
| Design flow | The required flow from the selected heat pump's design, not an assumed flow for its nominal heat output |
| Flow and return | 12 m + 12 m = 24 m of measured tube in this example |
| Fluid | Actual water or antifreeze type, concentration and design temperature; use data valid for that fluid |
| Fittings and components | Count both legs and include the selected valves, strainer, connections and other components |
| Available external pump head | Use the manufacturer's available head at the required flow; avoid subtracting internal losses twice |
| Candidate tube size | Compare the documented pressure loss of each suitable Ridgeline size at the required flow |
The complete circuit loss is the tube loss over both legs plus the losses of fittings and other components at the same flow. Compare that total with the available external pump head in matching units. Static building height is not simply added as circulation loss in a filled closed loop; filling pressure, expansion and air removal are separate design checks.
For a project check, send the heat-pump make and model, required flow, available head, route drawing, component list and fluid details to the Ridgeline technical team. Use the current technical data sheets and manufacturer's installation instructions before final selection.
What Good Heat-Pump Pipework Needs
Good ASHP pipework should:
- match the hydraulic design
- minimise unnecessary elbows and fittings
- route cleanly through walls and tight spaces
- be insulated appropriately, especially outdoors
- tolerate antifreeze and heating-system conditions
- avoid avoidable pressure drop
- be quick to install without compromising flow
Why Flexible Stainless Steel Helps
Rigid pipework can make ASHP installs slower, especially where the external unit is away from the plant room or where the route passes through awkward building fabric.
Ridgeline lets the installer create long continuous runs, route around obstacles and reduce fitting count. That is especially valuable outdoors and through walls, where every joint adds labour and future maintenance concern.
Insulation Still Matters
Ridgeline does not remove the need for correct insulation. Flow and return pipework should be insulated to suit the system design, outdoor exposure, temperature, condensation risk and manufacturer guidance.
The pipe solves routing and material issues. The insulation still solves heat loss and environmental exposure.
Select The Tube, Fittings And Support
- Compare the Ridgeline tube and P1 fitting range against the project duty.
- Check current data sheets and approval schedules for the exact products.
- Use the heat-pump calculator for the route comparison.
- Read the flexible stainless routing guide for awkward external-to-internal runs.
- Ask the technical team to review the project inputs and selected configuration.
FAQs
Select the size using required flow, full flow-and-return length, fluid conditions, component losses and available external pump head. Compare the actual Ridgeline pressure-loss data; R-32 HP is an option for heat-pump primary pipework, not an automatic choice for every installation.
Ridgeline can be used for ASHP flow and return where correctly specified and insulated. External runs must be protected and insulated according to the system design and installation guidance.
Yes, if it is correctly sized, rated and installed. Flexibility can reduce fittings and simplify awkward routes, but hydraulic sizing still matters.
Corrugation affects per-metre friction, so sizing matters. At system level, fewer elbows and fittings can offset route losses. Always use the Ridgeline data sheet for pressure-drop design.