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How to Survey Existing Pipework for a Heat Pump
A practical guide to tracing, measuring and recording existing heating pipework.
- Last updated: September 2026
- Heat Loss Hub · For Installers
A heat-pump pipework survey should establish main heating flow and return, pipe diameters, pipe materials, pipe routes, size transitions, branches, manifolds, what each section serves, visible circuit lengths, existing pumps and valves, hidden sections, potential connection points, photographic and video evidence, and any uncertainty.
The aim is not to decide immediately whether the existing pipework is suitable. The aim is to create a reliable map of what is already there so the hydraulic design can assess it properly.
KEY TAKEAWAY
The survey records the pipework that exists. The hydraulic calculation determines whether it can carry the required flow.
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Send us the completed pipework survey and we’ll assess whether the existing system can carry the required flow.
What Information Should Be Recorded?
| Information | Why It Matters |
|---|---|
| Pipe reference | Keeps the section traceable |
| Function | Shows what the section does |
| Diameter | Supports hydraulic assessment |
| Material | Helps establish pipe characteristics |
| From / to | Defines the route |
| What it serves | Shows downstream load |
| Size transitions | Identifies changes in capacity |
| Visible length | Useful for later pressure-loss assessment |
| Hidden length | Shows uncertainty |
| Manifold connection | Important in branch systems |
| Pumps/valves | Describes the existing arrangement |
| Photos/video | Provides evidence |
| Confidence | Distinguishes confirmed from inferred |
A pipe measurement becomes useful when the designer knows where it is, where it goes and what it serves.
Start at the Plant and Follow the Heat
The most useful way to survey existing heating pipework is to start at the plant area and work outward. Follow the system in this order:
Heat source / plant area → Main flow and return → Zones or manifolds → Distribution branches → Final radiator connections
This is much more useful than measuring isolated sections of pipe around the property.
KEY TAKEAWAY
Start at the plant and follow the heat through the building. The aim is to understand the structure of the system, not just collect random pipe sizes.
Give Every Pipe Section a Reference
A simple reference system keeps the survey organised. For example: PIPE-01, PIPE-02, PIPE-03.
Each record should ideally include reference, location, function, diameter, material, from, to, what it serves and confidence.
Example: PIPE-01 — 22mm copper — Main heating flow — Plant room → hallway floor void — Serves ground-floor distribution.
This allows photographs, notes and later calculations to stay linked to the correct section.
Identify the Main Flow and Return
Where possible, identify and record main heating flow, main heating return, diameter, material, direction and accessible route.
If the function of a pipe cannot be confidently established, record the pipe accurately but leave its function uncertain. For example: “22mm copper — function uncertain”. That is more useful than a confident but incorrect assumption.
KEY TAKEAWAY
If the function cannot be confirmed, record the pipe accurately and leave the function uncertain.
Measure Pipe Diameter
Record the actual accessible pipe diameter where possible. Common external pipe sizes found in UK domestic heating systems include 8mm, 10mm, 12mm, 15mm, 22mm and 28mm.
The important point is to record what is genuinely visible or measurable. Do not assume the entire system is the same size because one pipe beside a radiator is 10mm or 15mm.
KEY TAKEAWAY
The pipe visible beside the radiator does not necessarily tell you the size of the distribution pipe under the floor. If the pipe size cannot be confirmed, record the uncertainty.
Record Pipe Material
Where identifiable, record the pipe material. Common examples include copper, plastic, steel and mixed systems.
For plastic pipework, photograph any visible manufacturer or product markings where possible. This can be useful because outside diameter alone may not establish the exact internal bore or pipe construction.
KEY TAKEAWAY
Outside diameter alone may not tell you the internal bore of a plastic pipe. Do not guess the product if the markings are not visible.
Trace the Route
For each identifiable section, try to establish where it starts, where it goes, where it becomes hidden, where it reappears and what it appears to serve.
22mm copper visible leaving plant room → Enters floor beside doorway → Reappears in hallway cupboard → Reduces to 15mm
This creates a much more useful record than simply writing “22mm pipework present.”
Do not survey pipe size without surveying where that pipe sits in the system.
Record Pipe-Size Transitions
Pipework often changes diameter as it moves through the property. Common examples might include 28mm → 22mm, 22mm → 15mm, or 15mm → 10mm.
Record where each transition occurs and what remains downstream. For each transition, note location, upstream size, downstream size and what the smaller section serves.
This matters because a small section close to one radiator has a very different role from a small section feeding several rooms.
KEY TAKEAWAY
A pipe measurement without its position in the system tells only half the story.
Distinguish Mains, Branches and Final Connections
It is useful to separate the pipework into broad categories.
Main Distribution
Carries combined system flow to larger parts of the property.
Branch Pipework
Feeds a group of radiators, a zone or another circuit.
Final Emitter Connection
Feeds one radiator or terminal unit.
The same pipe diameter can mean very different things depending on what it is required to carry.
KEY TAKEAWAY
The same pipe diameter can have a very different significance depending on what it is required to carry. A 10mm final radiator tail is not the same survey finding as a 10mm section feeding several radiators.
Record What Each Pipe Section Serves
Where possible, record whether each section serves the whole heating system, one heating zone, several radiators, one radiator, the cylinder coil, a UFH manifold, or another hydraulic component.
For example: PIPE-04 — 15mm copper — Serves Living Room RAD-01 and Dining Room RAD-01.
This gives the designer useful context later. The designer needs to know not only the pipe size, but the load sitting downstream of it.
How to Survey Microbore
If you find microbore or other small-bore heating pipework, record it carefully. Useful information includes diameter, material, where it starts, where it ends, what it serves, approximate visible length, whether it originates from a manifold, hidden route, number of emitters served, photos and confidence.
Do not automatically recommend that it is replaced. A short small-bore section serving one radiator is very different from a long small-bore distribution circuit serving several emitters.
KEY TAKEAWAY
Microbore should be surveyed, not automatically condemned. The hydraulic calculation should determine whether the pipework is suitable.
Explore: Microbore Pipework and Heat Pumps
Survey Manifolds Carefully
A manifold can reveal a large amount about the existing heating distribution. If one is present, record location, main flow size, main return size, number of branches, branch sizes, which rooms or circuits they serve where known, photographs and accessibility.
Do not assume the destination of every branch unless it can be confirmed. If the branches disappear into floors or walls, use Confirmed, Inferred or Unknown as appropriate.
KEY TAKEAWAY
A manifold can explain the whole distribution strategy, so it should never be treated as just another fitting.
Survey the Plant Area
The plant area is often the best place to understand how the system is arranged. Record where present main heating flow, main heating return, circulation pumps, zone valves, bypass, manifolds, buffer vessel, low-loss header, cylinder branch, UFH branch and heating zones.
Take one wide photograph showing how the plant area fits together, then add close-up photographs where detail is needed.
KEY TAKEAWAY
A collection of pipe close-ups is less useful than one image showing how the system fits together.
Record Pumps, Valves and Existing Hydraulic Components
The pipework survey should describe the existing system rather than redesign it. Where present, record items such as circulation pump, two-port valve, three-port valve, automatic bypass, buffer vessel, low-loss header, mixing valve and manifold.
The survey does not need to decide whether those components should remain.
KEY TAKEAWAY
The survey describes the existing system. The design decides what the new system requires.
Record Visible Pipe Lengths
Where useful, record approximate visible lengths of important sections. This may be particularly useful for microbore, long branches, main distribution sections and sections with multiple bends.
Do not create false precision where much of the route is hidden. For example, “Approx. 2.5m visible” is better than inventing a total circuit length that cannot be confirmed.
In existing properties, significant parts of the heating system may be hidden below floorboards, behind plasterboard, chased into walls, beneath solid floors, above ceilings, or inside boxing.
The survey should distinguish between what is known and what is assumed. A useful system is:
Confirmed
The pipe is visible and measured.
Inferred
The route is strongly indicated but cannot be seen continuously.
Unknown
The route cannot be established from the available evidence.
For example: “22mm copper confirmed leaving plant room. Route beneath hallway floor inferred. Exact upstairs branch arrangement unknown.”
KEY TAKEAWAY
Hidden pipework should remain hidden information — not become a confident assumption.
Should Floorboards Be Lifted?
Not every heat-pump survey requires intrusive investigation. Where important pipework is concealed: check accessible inspection points, review existing drawings where available, use photographs or video, record where pipes disappear and reappear, flag uncertainty, and arrange further investigation where genuinely required.
A homeowner completing a remote survey should not be asked to lift floors unnecessarily, remove fixed building fabric, open sealed equipment, expose unsafe pipework, or carry out work beyond their competence.
The aim is to collect useful evidence without creating unnecessary damage or risk.
Record a Potential Connection Point for the Heat Pump
Where possible, the survey should identify where the existing heating distribution could potentially be intercepted. Useful information includes accessible main flow, accessible main return, relationship to the proposed plant area, distance from the outdoor unit route, structural restrictions, wall or floor penetrations, and installation access.
The survey does not need to design the final connection.
KEY TAKEAWAY
The survey should show where connection may be possible. The design should determine how it is actually done. This information can reduce avoidable questions later in the design process.
Photos and Video
Use photographs to support the pipework record. Useful photographs may include plant overview, main flow and return, pipe diameter evidence, size transitions, manifolds, branches, radiator tails, existing pumps and valves, unusual components and potential connection area.
Video can be especially useful where the route matters. For example: “This pipe leaves the plant room, crosses the utility, enters the floor here and appears again in the hallway cupboard.”
KEY TAKEAWAY
Use photographs to show the pipe. Use video to show where the pipe goes.
For a full photo guide:
Example Pipework Survey Record
A useful pipework record might look like this:
| Field | Example |
|---|---|
| Reference | PIPE-01 |
| Area | Utility room |
| Function | Main heating flow |
| Material | Copper |
| External diameter | 22mm |
| From | Existing boiler |
| To | Ground-floor distribution |
| Visible length | Approx. 2.5m |
| Size transition | Reduces to 15mm |
| Serves | Multiple ground-floor radiators |
| Route confidence | Partially confirmed |
| Photo | Yes |
| Video | Yes |
| Notes | Continues below floor |
A second section might be:
| Field | Example |
|---|---|
| Reference | PIPE-07 |
| Area | Bedroom 1 |
| Function | Radiator branch |
| Material | Copper |
| External diameter | 10mm |
| Origin | Upstairs manifold |
| Serves | Bedroom 1 RAD-01 |
| Visible length | Approx. 1.2m |
| Hidden section | Yes |
| Confidence | Partially confirmed |
A useful pipework survey creates a map, not a list of diameters.
What Happens After the Pipework Survey?
The survey itself does not determine whether the pipework is hydraulically suitable. The process normally looks like this:
Survey records what pipework exists → System design establishes the required heat transfer → Required design flow is calculated → Pipe internal diameter is assessed → Velocity is checked → Pressure loss and circuit resistance are considered → Available pump head is checked → Design determines: retain / alter / replace / investigate further
KEY TAKEAWAY
The survey records the route and evidence. The hydraulic calculation decides whether the pipework is adequate.
Common Pipework Survey Mistakes
Measuring Only Radiator Tails
Problem: The final radiator connection may be much smaller than the main distribution pipework.
Better: Trace the system back toward the branch or main distribution where possible.
Assuming All Pipework Is the Same Size
Problem: Heating systems commonly change diameter throughout the property.
Better: Record each size transition.
Recording Diameter Without Route
Problem: A note saying “15mm pipe” does not explain what that pipe does.
Better: Record where it starts, where it goes and what it serves.
Missing Size Transitions
Problem: A restriction may exist upstream or downstream from the point being measured.
Better: Follow the pipe as far as reasonably practical.
Seeing Microbore and Immediately Recommending a Re-Pipe
Problem: Small-bore pipework should not be condemned from diameter alone.
Better: Record the route, length and downstream load for later hydraulic assessment.
Missing a Manifold
Problem: A manifold may explain how several apparently separate small-bore circuits are supplied.
Better: Check cupboards, plant areas and accessible distribution points.
Not Recording What Each Branch Serves
Problem: The designer cannot understand the duty of the section.
Better: Link branches to rooms, zones or emitters where possible.
Guessing Concealed Pipework
Problem: An assumed route can quickly become treated as fact.
Better: Use confirmed, inferred and unknown classifications.
Taking Only Close-Up Photographs
Problem: The designer sees individual pipes but not how the system connects.
Better: Take a wide overview as well as detailed photographs.
Ignoring Plastic Pipe Markings
Problem: Two visually similar plastic pipes may not have identical internal dimensions.
Better: Record product markings where visible.
Missing Existing Pumps and Zone Valves
Problem: The existing system architecture remains unclear.
Better: Record the components as part of the plant survey.
Not Recording a Potential Connection Point
Problem: This can create avoidable follow-up work later.
Better: Record accessible main flow and return sections near the proposed heat-pump route where possible.
A pipe measurement without context is evidence, but it is not yet a usable system map.
Pipework Survey Completeness Check
Before leaving the property, confirm: plant area recorded, main flow identified where possible, main return identified where possible, main pipe sizes recorded, pipe material recorded, size transitions recorded, main routes traced, branches identified, manifolds recorded, what each branch serves recorded where possible, microbore sections recorded, existing pumps and valves recorded, hidden routes marked appropriately, potential connection area recorded, photos taken, video taken where useful, confidence recorded, and critical unknowns flagged.
The result should then be: Pipework survey complete, or Further information required.
Frequently Asked Questions
Start at the existing heat source or plant area and trace the heating system outward. Record main flow and return, pipe sizes, materials, routes, size transitions, branches, manifolds, what each section serves, hidden sections, existing components, photos and video, and any uncertainty.
Record the actual accessible sizes you can confirm. Typical domestic systems may contain several different diameters rather than one pipe size throughout. The position of each section is as important as its diameter.
Where the pipe is safely accessible, measure or identify the outside diameter. If you cannot confirm the size, record it as uncertain rather than guessing.
Sometimes. Its suitability depends on more than diameter alone. Important factors include required flow, what the pipe serves, length, internal bore, pressure loss and wider circuit design. The survey should record the evidence and leave the decision to the hydraulic assessment.
No. Some microbore sections may be suitable while others may need alteration. The correct decision depends on the duty and hydraulic characteristics of the actual circuit.
Not necessarily. A radiator may have 10mm or 15mm tails while being supplied from larger distribution pipework elsewhere. That is why the survey should trace the system rather than relying on the radiator connection alone.
Record where the pipe is visible, where it disappears and where it reappears. Use Confirmed, Inferred and Unknown. Do not invent a route that cannot be established.
Not necessarily. Use accessible evidence first. Further investigation may be justified if a critical part of the design depends on information that cannot otherwise be established.
Record location, main flow and return sizes, number of branches, branch sizes, which circuits they serve where known, photos and accessibility.
It is a point where the pipe changes diameter, for example 22mm to 15mm or 15mm to 10mm. These transitions should be recorded because they help the designer understand how the distribution system is arranged.
Yes, where they are visible. Manufacturer and product markings can help identify the pipe more accurately.
Yes. They help describe the existing hydraulic arrangement. The survey does not decide whether they remain in the final design.
Useful pipework photos include plant overview, main flow and return, pipe sizes, size transitions, manifolds, branches, existing pumps and valves, and potential connection points. Video is particularly useful for showing routes.
A homeowner can usually provide photographs, video and measurements of safely accessible pipework. They should not be asked to dismantle building fabric, open sealed equipment or investigate anything unsafe. Technical interpretation should remain with the installer or designer.
The designer considers factors including required heat transfer, design flow rate, pipe internal diameter, velocity, pressure loss, circuit resistance and available pump head. The decision should come from the hydraulic calculation rather than pipe diameter alone.
No. Some existing pipework may be suitable. Other sections may require targeted alteration. A complete re-pipe should not be assumed without assessing the actual system.
Map the Existing System Before Deciding What Needs to Change
A useful pipework survey should establish pipe sizes, pipe materials, routes, size transitions, branches, manifolds, what each section serves, existing hydraulic components, hidden sections, potential connection points, confidence, and photographic and video evidence.
It should not guess whether a pipe is adequate simply because of its diameter.
The survey records the pipework that exists. The hydraulic calculation determines whether it can carry the required flow.
HEAT PUMP PIPE SIZING SERVICE
Send us the completed pipework survey and we’ll assess whether the existing system can carry the required flow.
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