Hide Central Heating Pipes on Walls (Trunking)
The cleanest way to conceal exposed heating pipes is to build a removable trunking box sized around the insulated pipes, fittings and required movement. Keep valves and joints accessible, retain continuous insulation, and avoid blocking room or appliance ventilation. Before work begins, check the wall, pipe route and local code requirements, especially where the route crosses a fire-rated wall or floor.
As homes move toward cleaner, simpler finishes, surface-mounted heating pipes can stand out against a carefully planned wall. Trunking, also called a pipe box or enclosure, can make the route neater without cutting into the wall. The key is to treat it as a serviceable enclosure, not a sealed decorative cover.
I start by tracing the full pipe run and noting every bend, support, valve and joint. That simple survey often changes the design: a narrow box may hide a straight run, but not a valve that needs a hand and tool to reach. The aim is to conceal the pipes while preserving safe operation and future repair access.
Plan the Route and Check the Wall
A route survey is a check of the pipes, wall and services before you size or fix the enclosure. It helps you spot joints, valves, pipe movement, insulation and possible clashes with wiring or other plumbing. It also shows whether the wall or floor is fire-rated, which affects how any opening must be treated.
First identify the pipe material and the system’s expected operating temperature. Check where pipes enter or leave the wall, where supports hold them, and whether valves, unions or air vents sit along the route. A union is a joint designed to be disconnected for service. Do not plan to bury one behind a fixed cover.
Measure the outside of the insulation, not just the bare pipe. Include the widest fittings and bends, then add room for movement and access. Check the wall construction and look for electrical cables or other services before drilling or fixing a frame. If you cannot confirm what lies behind the wall, get suitable advice before making holes.
There is no universal code-mandated trunking size or pipe-to-box clearance. Follow the locally adopted plumbing, mechanical and building codes, along with the instructions for the pipe, insulation and enclosure materials. Requirements vary by location and code edition.
Illustrative retrofit scenario: A pair of pipes runs along a hallway wall, with a valve near one end. A narrow cover may look tidy, but if it hides the valve, a future repair could mean removing the whole enclosure. I would mark the valve location first, then plan a removable panel there and size the box around the insulated pipes.
Preserve Clearances, Movement and Service Access
Clearance is the open space between the insulated pipe and the inside of the enclosure. It gives the pipe room to move and helps prevent the cover from pressing on insulation or fittings. Access means having enough space to reach a valve or joint with the hand and tools needed for inspection or repair.
As a design recommendation, aim for at least 25 mm of clear space between the insulation and the trunking interior where practicable. Treat this as a starting point, not a code minimum. Increase it around bends, larger fittings, moving sections and service points. Do not clamp pipes in place with the box frame.
Copper expands as it heats. Its approximate expansion rate is 16.5 × 10⁻⁶ metres per metre per kelvin. For example, a 10-metre copper run heated through 50 K lengthens by about 8.3 mm. The actual pipe route and support layout affect how that movement occurs, so allow space at bends, supports and enclosure ends rather than assuming the pipe will move in one direction.
Keep insulation continuous along the pipe and over fittings where practicable. Choose insulation rated for the system’s maximum operating temperature, and use a thickness that meets the locally adopted energy code. There is no single thickness that suits every system, climate or location.
| Detail to plan | Design check | Why it matters |
|---|---|---|
| Pipe clearance | Aim for at least 25 mm from insulation to enclosure, where practicable | Allows room for movement and avoids pressure on insulation |
| Access opening | Consider a removable opening of at least 300 × 300 mm at service points | Provides a useful starting size; enlarge for the actual hand and tool access needed |
| Copper movement | A 10 m run heated through 50 K expands about 8.3 mm | Helps prevent a rigid enclosure from trapping the pipe |
| Insulation | Keep it continuous and rated for system temperature | Supports the intended insulation performance |
| Airflow | Do not treat trunking as a supply or return-air duct | No generic airflow rate applies to a pipe enclosure |
The 300 × 300 mm opening is a design recommendation, not a code minimum. Some valves need a larger opening, while a small service point may need a different layout. Test the access plan before closing the box: confirm you can reach and operate the item with the tools it requires.
Frame, Insulate and Finish the Trunking
The frame supports the enclosure panels without using the pipes as structural supports. It should leave the pipework free to move and keep insulation intact. Removable sections at service points make future checks easier, while a neat finish helps the box sit comfortably with the wall.
- Set out the box. Mark the route, panel edges, support points and access openings. Use the measured insulation and fittings to set the internal size. Allow more room where movement or servicing calls for it.
- Choose suitable fixings. Fix the frame to the wall with materials and fixings suited to the wall construction. Use suitable, non-corroding fixings. Avoid drilling where electrical or plumbing services may be present.
- Keep the pipe independent. Do not screw through, squeeze or clamp the pipes. Keep existing pipe supports in place unless a qualified professional determines they need adjustment. Do not use the enclosure frame to carry pipe weight.
- Fit insulation carefully. Keep or reinstate insulation along the full run, including fittings where practicable. Do not tightly pack insulation around a section that needs to move.
- Make service panels removable. Use a panel or access door at valves, unions, air vents and other service points. A screw-fixed removable panel can work where it can be opened without damaging the finish. Mark hidden valves on a plan or with a discreet label.
- Finish the surface. Match the cover to the wall, skirting or trim as appropriate. Before final fixing, check that panels can still be removed and that no edge presses against the pipes.
Trunking does not usually need vents simply because it encloses heating pipes. It is not a supply or return-air duct, and there is no generic airflow rate for it. Vent the enclosure only if the heating system design or product instructions require it. In all cases, do not block required room ventilation or an appliance’s combustion-air openings.
Verify Operation, Firestopping and Future Access
Verification is the final check before the enclosure is closed. It confirms that the pipes are sound, supports remain secure, insulation is continuous, and service points are reachable. If the route crosses fire-rated construction, the penetration must be dealt with using an appropriate listed firestop system for that specific wall or floor arrangement.
Before closing the panels, check the full run for leaks and confirm that supports are secure. Make sure the pipe can move without rubbing on the frame, and check that insulation has not been crushed or left with gaps. Open each access panel and confirm you can reach the valve or joint with the needed tool.
A fire-rated wall or floor is designed to resist fire for a stated period as part of an assembly. A pipe opening can affect that performance. Ordinary foam, caulk, or an improvised timber-and-gypsum box does not automatically preserve the rating. Use a firestop system listed for the specific wall or floor, pipe material and opening configuration, and follow its installation instructions and local code.
Illustrative fire-rated route: If heating pipes pass through a rated wall and then enter a surface enclosure, the box does not replace the need to protect the wall opening. The penetration needs the correct listed firestop treatment. If the assembly or pipe details are unclear, pause and ask a qualified professional or the local building authority before closing it.
I also check that future access will be obvious to someone who did not install the cover. A discreet label, a note on the home’s service plan, or a clearly removable panel can prevent unnecessary damage during a repair. Keep the enclosure removable at likely service points; do not permanently seal over valves, unions or likely leak points.
Conclusion and FAQs
A successful pipe enclosure hides the route without making the heating system harder to inspect or repair. Survey first, size from the insulated pipe and fittings, allow for movement, preserve service access, and follow local rules for the wall construction. The final check should happen before the last panel goes on.
Can I cover central-heating pipes with trunking?
Yes, if the enclosure leaves the pipes insulated, allows for movement, and keeps valves and joints accessible. Follow local codes and product instructions.
How much clearance should I leave inside a pipe box?
As a design guide, aim for at least 25 mm between the insulation and the enclosure where practicable. Add more around bends, fittings and service points.
How large should an access panel be?
A 300 × 300 mm opening is a useful design starting point at serviceable items, not a code minimum. Make it larger if the valve or fitting needs more hand or tool access.
Do heating-pipe enclosures need ventilation holes?
Not by default. The enclosure is not an air duct. Vent it only if the system design or manufacturer’s instructions call for it, and never block required room or appliance ventilation.
Can I hide a valve behind a fixed panel?
No. Keep valves, unions, air vents and other service items reachable through a removable panel or opening sized for the work required.
Will copper pipes move when they heat up?
Yes. A 10 m copper run heated through 50 K lengthens by about 8.3 mm. Allow movement at bends, supports and enclosure ends.
Should I keep insulation under the trunking?
Yes. Keep insulation continuous along the pipe and over fittings where practicable. Select material for the system’s maximum operating temperature and local energy-code needs.
Can I use ordinary foam around a pipe passing through a fire-rated wall?
Not as a substitute for an approved firestop system. Use a listed system suited to the wall or floor, pipe and opening, and follow its instructions.
Can trunking be fixed directly against the pipes?
No. The frame should support the enclosure, not clamp the pipework. Keep the pipes free to move and avoid crushing insulation.
Is there one code size for heating-pipe trunking?
No. There is no universal code-mandated trunking size or pipe-to-box clearance. Check the locally adopted codes and the manufacturers’ instructions.
(This article was written by one of our staff writers, Michael Donovan. Visit our Meet the Team page.)
