Home / For Installers / Hydraulic Design Service
FOR INSTALLERS · HYDRAULIC DESIGN
Heat Pump Hydraulic Design Service for Installers
Turn the heat-pump design into a working hydraulic system.
- Last updated: September 2026
- Heat Loss Hub · For Installers
Once the core heat-pump design is known, the next question is how the water side of the system should actually work.
Heat Loss Hub can design the hydraulic arrangement around the selected equipment, emitters and system constraints. The service can cover:
- Required system flow
- Minimum system volume
- Direct vs separated layout
- Buffers and volumisers
- Low-loss headers
- Internal and secondary pumps
- Zoning
- Bypass strategy
- Radiators and UFH
- Domestic hot-water integration
- Hydraulic schematic
KEY TAKEAWAY
We turn the heat-pump design into a hydraulic arrangement the installer can actually build.
GET IN TOUCH
Send us your core design information and we’ll return a clear, buildable hydraulic arrangement.
Hydraulic Design Only, if That Is All You Need
You do not have to outsource the entire heat-pump design. You may already have room-by-room heat-loss calculations, emitter sizing, heat-pump selection, cylinder selection, pipe sizes and your own MCS workflow.
You may simply need the water-side arrangement designed properly. Heat Loss Hub can take the completed design inputs and work out how the system should be connected and operated hydraulically. This can suit:
- MCS installers with their own design process
- Internal designers needing specialist hydraulic support
- Installers dealing with complex retrofit systems
- Businesses handling mixed radiator and UFH projects
- Companies needing an independent schematic
- Teams experiencing temporary technical backlog
You do not need to outsource the whole MCS design to outsource the hydraulics.
What Hydraulic Design Actually Decides
Hydraulic design should answer practical installation questions. For example:
- How should the heat pump connect to the heating system?
- What flow rate is required?
- Is hydraulic separation needed?
- Does the system need additional water volume?
- Is the internal heat-pump pump sufficient?
- Are secondary pumps required?
- How should heating zones behave?
- How should radiators and UFH work together?
- What happens when valves or zones close?
- How should the cylinder circuit be connected?
- What components are actually necessary?
The purpose is to turn the heat-pump design into a coherent water-side system.
Direct System or Hydraulic Separation?
One of the first hydraulic decisions is whether the heat pump can operate directly into the heating system.
Direct System
In a direct arrangement, the heat pump circulates through the heating distribution without a separate hydraulically isolated circuit. This can reduce components, pumping, complexity and heat losses. Where the system can maintain the required flow and volume reliably, a direct arrangement may be the simplest solution.
Hydraulically Separated System
In some projects, the heat-pump circuit and heating distribution may need to operate more independently. Hydraulic separation can be introduced using an appropriate arrangement where there is a defined reason to do so. Possible reasons may include different circuit flow requirements, multiple distribution pumps, complex zoning, high-resistance circuits and mixed emitter systems.
KEY TAKEAWAY
Hydraulic separation should be justified by the system, not added by default.
Buffer, Volumiser or Neither?
These components are often treated as though they all perform the same job. They do not.
Volumiser
A volumiser is used primarily to add water volume to the system. It may be required where the available connected system volume is lower than the heat pump needs under certain operating conditions.
Buffer
A buffer adds water volume and, depending on how it is connected, may also affect the hydraulic relationship between the heat pump and the heating circuit.
Neither
If the system already provides sufficient water volume, flow, open circuit and hydraulic stability, there may be no reason to add either component.
KEY TAKEAWAY
Buffers and volumisers should solve a defined problem, not appear automatically on every schematic. The design should identify the requirement first and choose the component second.
Minimum System Volume
Some heat pumps require a minimum amount of accessible water volume. That requirement can become particularly important during low-load operation, defrost, zoning and partial system closure.
The design should consider not just the total theoretical water content, but how much of that volume remains available to the heat pump during actual operation. Questions may include: how much water volume is connected? What happens when TRVs close? What happens when zone valves close? Does the heat pump still have access to sufficient volume? Is additional volume required?
KEY TAKEAWAY
The important figure is the usable water volume the heat pump can actually see. If additional volume is required, the design should explain why and how it is being provided.
Minimum Flow Rate
The heat pump also needs sufficient water flow. That flow needs to be protected through different operating conditions. The hydraulic design should consider a fully open heating system, a partially closed system, zone valves, TRVs, UFH actuators, DHW operation and multiple circuits.
A system that works when every valve is open may behave very differently once only one small zone remains active.
KEY TAKEAWAY
Minimum flow has to be protected by the system architecture, not assumed. The design should make clear how this is achieved.
Pump Selection and Available Head
Water flow is only useful if the pump can overcome the resistance of the circuit. The design may need to consider required flow rate, pipework resistance, valves, fittings, heat exchangers, manifolds, emitters and the available head from the heat pump’s internal pump.
In some systems, the heat pump’s internal circulator may be sufficient. In others, it may not be.
KEY TAKEAWAY
A pump should be selected against the circuit it serves, not by habit. The aim is not to fit the largest pump available. It is to select the right pumping arrangement for the actual system.
When Is a Secondary Pump Required?
A secondary pump may be required where the heating distribution has a hydraulic requirement that cannot be served properly by the heat-pump circuit alone. Examples may include hydraulic separation, high-resistance distribution, long circuits, UFH manifolds, multiple heating circuits and mixed emitters.
The hydraulic design should establish what circuit the pump serves, required flow, required head and how it interacts with other pumps.
KEY TAKEAWAY
Adding another pump without understanding its purpose can create a different hydraulic problem.
Pump Interaction
Multiple pumps do not automatically improve a system. Poorly arranged pumps can compete with each other, distort flow, create unwanted mixing, reduce heat-pump flow, increase electricity use and make commissioning difficult.
The schematic should make each pump’s role clear.
KEY TAKEAWAY
More pumps do not automatically create better hydraulics. Where multiple pumps are required, their interaction should be part of the design.
Zoning and Closing Circuits
Zoning can create significant hydraulic changes. The system may include motorised zone valves, TRVs, UFH actuators, separate floors and different room groups.
The design needs to ask: what happens hydraulically when most of the system closes? The remaining open circuit still needs to maintain the conditions required by the heat pump. This may affect minimum flow, minimum system volume, pump operation, bypass strategy and control strategy.
KEY TAKEAWAY
Zoning should therefore be treated as part of the hydraulic design rather than simply an electrical control decision.
Bypass Strategy
A bypass may be appropriate in some systems. It should have a clear purpose — that may include maintaining a defined flow path under certain operating conditions.
The design should establish whether a bypass is required, where it should be located, what condition it protects against and how it interacts with zoning and pumps.
KEY TAKEAWAY
A bypass should not simply be added because one existed on the old boiler system.
Radiators and UFH Together
Mixed emitter systems need particular care. A property may include radiators, underfloor heating, fan convectors and towel rails. These circuits may have different flow requirements, pressure losses, operating temperatures and control requirements.
The design may therefore need to consider UFH manifold flow, mixing, separate pumping, zoning and interaction with radiator circuits.
KEY TAKEAWAY
Mixed emitters should be designed as one hydraulic system, not two disconnected ideas. The final arrangement should work as a complete system.
Where the underfloor heating pipework itself also requires design, we offer a dedicated UFH CAD drawing and calculation service. This can be combined with our hydraulic design service or commissioned separately. Explore Underfloor Heating Design →
Domestic Hot-Water Integration
The cylinder circuit is part of the hydraulic design. It should not be added after the heating side has already been decided. The design may need to show cylinder connection, diverter valve, DHW priority, pumping arrangement, flow and return path, control intent and interaction with space heating.
KEY TAKEAWAY
The cylinder circuit is part of the hydraulic design, not an add-on after the heating circuit is finished. The schematic should make the change between space heating and hot-water operation clear.
Existing System Components
Existing properties may already contain pumps, buffers, low-loss headers, bypass valves, zone valves, manifolds and controls. Those components should not automatically be retained. They should be assessed against the new heat-pump design. Possible outcomes include:
Retain
The existing component still serves a useful, defined purpose.
Remove
The component is unnecessary in the new arrangement.
Replace
The component is unsuitable for the new flow or duty.
Reconfigure
The component can remain but needs to be connected differently.
KEY TAKEAWAY
Existing components should be justified by the new system, not retained because they are already there.
Why Is Each Component There?
A good hydraulic design should be able to explain the role of every major component.
| Component | Typical Purpose |
|---|---|
| Volumiser | Adds system water volume |
| Buffer | Adds volume and may affect hydraulic interaction |
| Low-loss header | Provides hydraulic separation |
| Secondary pump | Serves a defined distribution circuit |
| Bypass | Maintains a defined flow path where required |
| Diverter valve | Switches between heating and DHW |
| Zone valve | Opens or closes a defined heating zone |
The exact purpose depends on the project.
KEY TAKEAWAY
Every hydraulic component should solve a defined system requirement. If nobody can explain why a component is there, it is worth questioning whether it belongs in the design.
What You Need to Send Us
Typical project inputs include:
- Selected heat pump
- Whole-property design load
- Design flow temperature
- Design return temperature
- Required system flow
- Emitter schedule
- Pipe layout
- Pipe sizes
- Approximate pipe lengths
- Cylinder details
- UFH details
- Zoning
- Existing pumps
- Existing valves
- Existing buffer or low-loss header
- Plant-room constraints
- Manufacturer hydraulic requirements
- Relevant drawings, sketches and photos
The more complete the information, the easier it is to produce a clear hydraulic solution. Where something critical is missing, a query can be raised before the system arrangement is finalised.
What You Receive
The exact output depends on the agreed design scope. A hydraulic design package may include hydraulic schematic, required heat-pump flow, minimum system-volume assessment, direct or separated system decision, buffer or volumiser requirement, pump requirements, secondary pump duty where applicable, hydraulic separation strategy, zoning strategy, bypass strategy, DHW arrangement, component schedule, design notes, assumptions and revision reference.
The output should show not only what components are required, but why they are there. The aim is to give the installer something that can be understood and built from.
Example Hydraulic Design Decisions
Different projects can lead to very different outcomes.
Example A — Direct System
The existing heating circuit can provide required flow, sufficient volume and acceptable resistance. The internal heat-pump pump is suitable.
Result: Direct arrangement with no buffer or hydraulic separation.
Example B — Additional Volume Required
The distribution works hydraulically but does not provide enough usable water volume under the expected operating conditions.
Result: Volumiser added for a defined minimum-volume requirement.
Example C — Hydraulic Separation Required
The heat pump and distribution circuits cannot reliably operate at the same flow conditions.
Result: Hydraulic separation introduced with clearly defined primary and secondary circuits.
Example D — UFH Circuit Requires Secondary Pumping
The main radiator circuit can operate directly, but the UFH manifold has a different flow/resistance requirement.
Result: Dedicated UFH pumping arrangement incorporated into the schematic.
The correct answer depends on the project. Not on a standard template.
The Hydraulic Schematic
The hydraulic schematic is one of the main outputs of the service. Depending on the project, it may show heat pump, cylinder, primary flow and return, pumps, motorised valves, diverter valve, buffer, volumiser, low-loss header, radiator circuits, UFH manifold, bypass, sensors, controls intent and zone arrangement.
The purpose is not to make the drawing unnecessarily complicated. It is to make the intended system operation clear.
KEY TAKEAWAY
The schematic should make the intended water-side operation understandable before installation starts. A good installer should be able to look at the drawing and understand how water is expected to move through the system in the main operating modes.
What Is Not Included in Hydraulic-Design-Only?
Hydraulic design is one part of the complete heat-pump design process. Unless separately agreed, it does not automatically include:
- Room-by-room heat-loss calculation
- Radiator sizing
- Heat-pump model selection
- Cylinder sizing
- Electrical design
- DNO application
- Full MCS administration
- Complete project handover pack
You can retain those stages internally. Or Heat Loss Hub can provide a wider design service where required.
Explore: Outsourced MCS Heat Pump Design
Revisions and Design Changes
Hydraulic design depends on the equipment and layout it was based on. If the system changes, the hydraulic design may also need to change. Examples include a different heat pump selected, emitter schedule changed, pipe sizes altered, additional heating zone added, UFH introduced, cylinder changed, buffer added or removed, different plant-room layout or control strategy changed.
A small physical change can sometimes have a larger hydraulic effect.
KEY TAKEAWAY
If the system architecture changes, the hydraulic design should change with it. Revised schematics should be clearly identified so the installer knows which issue is current.
One Project, Complex Jobs or Ongoing Support
You can use the service for:
One Difficult Project
A system is technically awkward and you want a dedicated hydraulic solution.
Occasional Specialist Support
Your team handles normal systems internally but needs help on more complex arrangements.
Internal Design-Team Overflow
Your own technical team is at capacity.
Ongoing Hydraulic Support
Heat Loss Hub becomes the external hydraulic-design resource behind your business.
You remain in control of how much of the wider design process is outsourced.
White-Label Hydraulic Design
Hydraulic design can also sit behind your own customer relationship. Depending on the agreed arrangement, Heat Loss Hub completes the technical work, your business remains customer-facing, your customer remains your customer, schematics can sit within your wider design pack and branding can follow the agreed delivery model.
This can add specialist hydraulic capability without changing the way your customer experiences your business.
Hydraulic Design Quality Checklist
A useful hydraulic design should let you answer:
- What flow does the heat pump require?
- Is minimum flow protected?
- Is minimum system volume satisfied?
- Is the system direct or hydraulically separated?
- Why is any buffer present?
- Why is any volumiser present?
- Why is any low-loss header present?
- Is the heat pump’s internal pump sufficient?
- Are secondary pumps required?
- What circuit does each pump serve?
- What happens when zones close?
- How is DHW integrated?
- How do mixed emitters operate?
- What assumptions were made?
- Which schematic revision is current?
If those questions cannot be answered, the hydraulic design may not be complete enough to install from.
Frequently Asked Questions
Yes. If the building, emitter and equipment design is already established, Heat Loss Hub can complete the hydraulic stage and return the schematic and design notes to your team.
Depending on the agreed scope, this can include flow requirements, system volume, direct vs separated arrangement, pumps, buffers or volumisers, zoning, DHW integration and hydraulic schematic.
Not automatically. A buffer should be used where it solves a defined system requirement. The design should identify that requirement rather than assume every heat pump needs one.
Possibly. A volumiser may be useful where the system needs additional accessible water volume without necessarily requiring hydraulic separation. The actual requirement should be calculated for the project.
A volumiser primarily adds water volume. A buffer also adds volume but, depending on its connection arrangement, can affect the hydraulic relationship between the heat-pump circuit and distribution system.
A low-loss header may be useful where hydraulic separation is required between circuits with different flow characteristics. It should not be treated as a default component.
A direct system can be simpler and may reduce unnecessary components where the system can maintain the required flow, volume and hydraulic conditions. However, some systems have genuine reasons for separation. The correct choice depends on the project.
Not necessarily. The design should first establish whether the heat-pump and distribution circuits can operate together reliably. If they can, separation may not be required.
The connected water volume is assessed against the heat pump’s requirements and the way the system will operate. Zoning and closing valves can affect how much usable volume remains available.
Sometimes. The available pump head needs to be compared with the resistance of the actual circuit at the required flow.
A secondary pump may be needed where a distribution circuit has its own flow or resistance requirement, or where hydraulic separation is used.
The hydraulic design needs to consider the different flow, temperature and control requirements of each circuit. This may involve separate pumping, manifolds or mixing depending on the system.
The design should ensure that minimum flow and usable water volume remain acceptable under the expected operating conditions. This may affect the zoning and bypass strategy.
Yes, where the schematic is included in the agreed hydraulic-design scope.
Pipe sizing can be included or provided separately. If you already have a completed pipe schedule, the hydraulic design can use those figures as an input. Explore Heat Pump Pipe Sizing Service for Installers.
Need the Hydraulic Arrangement Without Outsourcing the Whole Heat-Pump Design?
Send us the core design information. We turn it into a clear water-side arrangement covering flow, system volume, pumps, separation, zoning and domestic hot-water integration.
SUBMIT A PROJECT
Send us your core design information and we’ll return a clear, buildable hydraulic arrangement.
Explore: Heat Pump Design for Installers