Quick answer: Measure between the centre-lines of the connections or pipes being compared, not between their outside edges. Record body width separately. Cheap Radiator towel rails in this range have connection centres 50mm less than body width, but the selected valve arrangement still needs checking.
Part of our small-bathroom towel radiator buying guide. This article focuses on matching the radiator connections to the pipework.
Pipe centres and body width are not the same
Body width is the overall side-to-side dimension of the radiator. Connection centres describe the distance between the centre-lines of its inlet and outlet connections. People also use “pipe centres” for the spacing of existing pipework, so make sure both people are discussing the same points on the installation.
A radiator can match the old body width while having different connection positions. It can also have matching radiator connections but require a different pipe route because the valves are different.
Examples from our towel radiator range
| Radiator body width | Listed connection centres |
|---|---|
| 200mm | 150mm |
| 300mm | 250mm |
| 400mm | 350mm |
| 550mm | 500mm |
| 650mm | 600mm |
These examples reflect the Cheap Radiator towel rail range discussed here. They are not a universal rule for radiators from other ranges or manufacturers. Check the exact product details and drawing before committing to the pipework.
How to record an existing installation
- Identify which two centre-lines you are measuring: radiator connections, valve connections or the existing pipes.
- Measure centre-to-centre and write the result in millimetres. Outside-edge spacing is a different number.
- Record where the pipes emerge: through the floor, from the wall or from another direction.
- Record the pipe diameter and the existing valve arrangement.
- Take a straight-on photograph and a side photograph that show the valves and wall position.
If the centres are difficult to identify, ask an installer to measure them. A few millimetres can matter when pipework is fixed through a finished tiled floor or wall. Do not force or bend connections to make a radiator fit.
Why the valves change the comparison
A straight valve keeps its main connection path in line; an angled valve changes direction. Valve body and tail dimensions can therefore change where the finished pipes need to meet the radiator. Check the actual valve drawing and dimensions alongside the radiator connections.
Use our valve selection guide to identify the questions to ask. When preserving existing pipework, compare the complete radiator-and-valve arrangement rather than subtracting 50mm from a new body width and assuming the job is settled.
Pipe diameter is a separate check
An 8mm, 10mm or 15mm pipe-size option describes a different part of the connection from the radiator’s inlet thread. Matching the finish, or seeing a familiar nominal thread size, does not by itself prove that the valve fits the pipework. Check the product specification and any required reduction fittings.
For replacement work, also confirm the mounting positions, projection and wall condition. Use the fitting information supplied for the exact model rather than an installation drawing for a different product.
Use the measurements to shop
A 150mm connection-centre requirement may lead you to compare our 200mm-wide black rails and 200mm-wide chrome rails. A 500mm requirement corresponds to listed centres on our 550mm-wide chrome range. In each case, confirm the valve arrangement, height and heat output before ordering.
For an electric or dual-fuel proposal, Electrical Safety First’s bathroom guidance provides independent safety advice. Have a registered electrician confirm the electrical installation separately from the pipe measurements.
What should I send for help?
Send the centre-to-centre measurement with the exact measuring points identified, pipe diameter, photographs and the proposed radiator. Include whether moving the pipework is an option. This makes a compatibility discussion much more useful than a photograph of the radiator front alone.
Questions about pipe centres
Practical answers to help with the choices covered in this guide.
Should I measure between pipe edges or centre-lines?
Measure between the relevant centre-lines and state which points you measured. Outside-edge spacing is a different dimension. Keep body width, radiator connection centres and existing pipe spacing separate.
Does subtracting 50mm from width guarantee my old pipes will fit?
No. That difference describes the radiator connection centres in our ranges. Valve dimensions, pipe route and projection still determine the assembled fit; other radiator designs may use different spacing.
Is pipe diameter the same as the radiator connection thread?
No. The pipe-side diameter and radiator-side thread are separate specifications. Check both, including any required reduction fittings, rather than choosing from finish or nominal width.
For the full fitting checklist, see the towel radiator valves and fittings guide. Browse narrow towel radiators once you have confirmed the measurements and fittings for your installation.
For the full checklist, see our guide to replacing a bathroom radiator with a heated towel rail.