Hepworth System Clamps - Compatibility with Plastic Piping

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Clips for the Hepworth system – compatibility with plastic pipe

The Hepworth system belongs to proven technologies in the field of installation of heating and distribution systems. The plastic pipes of this system have since their introduction to the market gained a solid place in Slovak and Czech installation projects – both in new buildings and in the reconstruction of older pipe systems. However, good pipe alone is not enough. Equally important, although at first glance less visible part of the entire installation are the clips and anchors, by which the pipe is attached to the wall, ceiling or structure.

In practice, I regularly encounter the situation where installers or handy homeowners pay maximum attention to the selection of pipes, but reach for anything that is just at hand when it comes to clips. The result? The pipe bends, makes noises when expanding, the clips crack or loosen after a few years. The aim of this article is therefore to thoroughly explain why the correct choice of clips for the Hepworth system is important, how compatibility with plastic pipe works and what to pay attention to during the actual installation.

Why system compatibility of clips matters

Hepworth plastic pipes are characterized by precisely defined outer diameters. Unlike metal pipes (copper, steel), where different manufacturers mostly maintain the same dimensions according to European standards, plastic systems are more specific – each manufacturer has its own series of dimensions, wall thickness and tolerances. Therefore, it is not true that any plastic clip for 15 mm will fit any 15 mm plastic pipe.

The Hepworth system uses pipes with outer diameters corresponding to the metric scale – typically 15 mm, 18 mm, 22 mm and larger dimensions according to the application. Clips specifically designed for the Hepworth system are designed so that their internal sleeve exactly matches the outer diameter of the pipe used. A seemingly small deviation of 0.5 mm can mean that the clip is either too loose (the pipe moves, vibrates, makes knocking sounds) or too tight (causing local stress in the pipe wall, premature damage).

In addition to the dimensions, the material of the clip also plays a role. Plastic anchors for the Hepworth system are typically made of polyamide (PA) or polypropylene (PP), or ABS – materials that are chemically compatible with plastic pipes and do not damage their surface. Metal clips without a plastic lining can cause surface abrasion or galvanic corrosion when in contact with plastic pipes, especially if there is a metal component in the system.

Overview of specific products – anchors for the Hepworth system

In the category of clips for the Hepworth system on the atria.sk website, you will find several types that cover the most commonly used pipe dimensions. Let's look at the individual products and their specific use in practice.

Simple anchors

Simple anchor 601004H is intended for smaller pipe dimensions – typically for an outer diameter of 15 mm, which is the most commonly used dimension in apartment heating installations. This is the clip I reach for most often in pipe runs to individual heating units, radiators or in wall-mounted floor heating runs before embedding.

Simple anchor 601005H covers a medium dimension – standard outer diameter of 18 mm. This size appears in horizontal pipe runs in the distribution loop, when connecting to manifolds or in vertical pipe runs in smaller apartment buildings. The difference from 601004H is not only in the diameter of the sleeve, but also in the overall construction of the anchor, which must support the greater weight of the pipe (filled with water) for the same length of section.

Simple anchor 601006H is intended for larger dimensions – typically an outer diameter of 22 mm. In practice, you will use it for the main distribution pipe, for example, when running from the boiler to the distributor/collector or for vertical pipes in two-storey houses. At this dimension, the weight of the full pipe is significantly higher, so the correct choice of anchor spacing is even more important.

Dual anchors

Dual anchors are structurally different from simple ones – instead of one sleeve, they contain two, thus securing two pipes side by side with a single anchor fixed to the wall. This makes practical sense wherever two parallel pipes (typically supply and return of the heating system) run at the same height and in the same direction.

Dual anchor 601007H is a version for smaller dimensions of parallel pipes – standard two pieces of 15 mm outer diameter. Compared to the use of two separate simple anchors, you not only save material and time (one anchor screw instead of two), but you also achieve a visually cleaner and more symmetrical installation. In practice, this is a big advantage for visible pipe runs in technical rooms or boiler rooms, where order matters.

Dual anchor 601008H is intended for larger dimensions – usually for two pipes of 18 mm or a combination of different diameters. This anchor is used in main pipe runs in boiler rooms and technical rooms, where the supply and return have the same or similar dimensions and run in parallel.

Compatibility of clamps with plastic piping – technical aspects

When discussing the compatibility of Hepworth plastic clamps with plastic piping, it is important to distinguish between several levels: dimensional compatibility, material compatibility, and functional compatibility (i.e., whether the clamp allows the pipe to function properly in terms of thermal expansion).

Dimensional compatibility

Hepworth plastic pipes are available in a range of outer diameters: 15 mm, 18 mm, 22 mm, and 28 mm (and larger in some applications). A corresponding clamp is available for each of these diameters. The inner diameter of the clamp must be larger than the outer diameter of the pipe – but not by much. Typically, the clearance between the pipe and the clamp is 0.2 to 0.5 mm, which allows the pipe to move axially (along its length) during thermal expansion, while at the same time preventing radial movement (swaying, vibrations).

If you were to use a clamp of a larger size (e.g., an 18 mm clamp on a 15 mm pipe), the pipe would "float" in it with a clearance of more than 1.5 mm on each side – which can be the source of problems with sagging of the pipe between clamps and with noise generation on long horizontal sections. On the other hand, a clamp of a smaller size would constrict the pipe and create local stress in the pipe wall at the point of fixation, which can lead to crack formation, especially under cyclic heating and cooling.

For more information on how to correctly determine the clamp size according to the outer diameter of the pipe, see the separate article What clamp size do I need – dimensional overview for 15 mm, 18 mm and other pipes in this Knowledge Centre.

Material compatibility

Plastic clamps for the Hepworth system are typically made of technical polyamide or polypropylene – materials that are:

chemically neutral towards common plastic pipes (PE-X, PE-RT, PPR, PB – materials used in the Hepworth system)
resistant to moisture and condensation (important in technical rooms and boiler rooms)
resistant to temperatures commonly encountered in heating systems (up to 90 °C continuously, up to 110 °C short-term)
able to maintain mechanical strength throughout the entire lifetime of the installation (10–30 years)

Metal clamps without a plastic lining in direct contact with plastic piping can cause surface abrasion of the pipe – especially during temperature changes, when the pipe moves. Surface damage to the plastic pipe usually does not mean immediate failure, but it reduces the lifespan and can be the source of later cracking. Further information on material comparisons can be found in the article Plastic vs. metal clamps for piping – advantages, disadvantages and suitable use.

Functional compatibility – thermal expansion

This is an aspect that many installers underestimate. Plastic piping has a significantly higher coefficient of thermal expansion than metal piping. For example, PE-X piping expands by approximately 0.9–1.2 mm per meter of length when heated from 20 °C to 70 °C. This means that a 10-meter section of pipe will extend by 9–12 mm when the heating system is turned on.

Clamps for the Hepworth system are designed as free supports – the pipe can slide axially within the clamp. This is a crucial difference from fixed supports, where the expansion would be released in the form of unpleasant curves (the snake effect), noise during movement, and in extreme cases, even damage to the joints. Clamps in the Hepworth system are primarily used for:

Radial (lateral) support of the pipe – they prevent lateral movement and vibrations
Supporting the weight of the pipe + medium (water) – they prevent sagging and bending
Guiding the pipe during thermal expansion – they allow axial movement, but control it

Fixed anchoring points (so-called fixpoints) in the Hepworth system are implemented in a different way – for example, through special clamps with a locking mechanism, or by embedding the pipe in a poured layer (e.g., in floor heating). The standard clamps/fixings discussed in this article are free (sliding) supports.

Clamp Spacings – Practical Values for the Hepworth System

Correct placement of clamps is just as important as choosing the right size. Too long spacing between clamps leads to pipe sagging (so-called sag effect), which is more visible in plastic pipes than in metal ones – plastic is less rigid. On the other hand, too dense clamping is unnecessarily costly and slows down installation.

For the Hepworth system, the following recommended clamp spacings apply for horizontal pipe runs:

Pipe Outer Diameter	Cold Water / No Medium	Hot Water / Heating
15 mm	800–1000 mm	600–800 mm
18 mm	900–1100 mm	700–900 mm
22 mm	1000–1200 mm	800–1000 mm
28 mm and above	1200–1500 mm	900–1100 mm

For vertical pipe runs (rising pipes), the spacings can be up to 50% greater compared to horizontal runs, since the pipe itself does not have to carry its own weight over the distance between clamps. However, for rising pipes, it is important to install a clamp at every change of direction and at the entry/exit of each floor level.

A more detailed guide on proper clamp placement can also be found in the article Clamp Spacings on Pipes – How to Properly Place Clamps.

Practical Scenarios from Installation Practice

Scenario 1: Pipe Distribution to Radiators in an Apartment Building

In a typical job – reconstruction of heating in a three-room apartment in a panel building – a horizontal pipe run leads from the manifold to six radiators. A 15 mm outer diameter pipe runs under the ceiling in long sections of 3–6 meters. In this case, I reach for the clamp 601004H with spacings of approximately 700 mm. On a 5-meter section, this means 7 clamps including a clamp at each branch and at the pipe entry into the wall.

In this project, the customer asked whether it would be sufficient to use clamps with a 1-meter spacing. In a building where heating is used seasonally, this might be acceptable – but on a 5-meter section with a medium temperature of 70 °C and ambient temperature of 20 °C, the pipe would expand by about 4.5–5 mm. With eight seasonal cycles (on/off), this is a real movement that with larger clamp spacing leads to visible sagging of the pipe. The customer would likely complain after the first season.

Scenario 2: Boiler Room with Parallel Supply and Return Lines

In a family house boiler room, both the supply and return lines run in parallel from the boiler to the manifold/collector – typically 18 mm or 22 mm outer diameter. The mutual distance between the pipes is 50–70 mm. Here, the double clamp 601008H is an ideal solution – one screw into the wall secures both pipes at once. Result: half as many wall holes, half as many wall anchors, faster installation, and a clean, aesthetic result.

In practice, for this scenario, I recommend combining: most of the spacings should be handled with a double clamp, but at branches and direction changes, use a single clamp for only one of the pipes (the one that branches off). This combination is completely standard and the manufacturers account for it.

Scenario 3: Pipe Run with Problematic Base Structure

In an older job – reconstruction of a boiler room in a house from the 1930s – we encountered a problem: the walls are made of soft brick with porous plaster, into which standard wall anchors do not fix reliably. In this case, it is important to use the correct type of anchor (anchors for hollow materials, chemical anchors) – clamps 601004H and 601005H have a mounting hole designed for standard plastic anchors with a 6 mm diameter, which is compatible with commonly available anchoring systems. The clamps themselves do not cause the problem – the weakness is always in the base, not in the clamp.

Installation of Plastic Clamps for the Hepworth System – Step by Step

The installation process is not complicated, but a few details determine the outcome:

Step 1 – Marking the route: Before drilling, mark the entire pipe route with a pencil (or a spirit level and marker), including clamp positions. Check the slope – horizontal pipes must have a minimum slope of 3–5 mm/m towards the drain point to allow for draining.
Step 2 – Drilling and anchors: Drill holes with a diameter of 6 mm and insert plastic anchors. The depth of the hole depends on the wall material – 40 mm is sufficient for concrete, 50 mm for brick.
Step 3 – Mounting the clamp: Place the clamp against the wall and screw it into the anchor with a screw. Do not overtighten – plastic clamps have a certain torque limit, and excessive tightening increases the risk of cracking the clamp body.
Step 4 – Inserting the pipe: Insert the pipe into the open clamp. Plastic clamps in the Hepworth system are mostly one-piece with elastic snap-in – simply push the pipe into the clamp and snap it in place.
Step 5 – Checking for freedom of movement: After securing the pipe, you should be able to manually move the pipe axially (along its length) by a few millimeters. If the pipe cannot be moved at all – the clamp is either undersized (wrongly selected) or was installed at an angle and is gripping the pipe too tightly.

The entire installation process is described in more detail in the article Installation of Plastic Clamps on Pipes – Step by Step.

Most common mistakes when selecting and installing clamps for the Hepworth system

Over the years of working with heating systems, I have seen a number of recurring mistakes. Here are the most common ones, along with their consequences:

Mixing up clamps for different systems: Using a clamp designed for copper or steel pipe on a Hepworth plastic pipe. Result – the clamp holds, but either with too much play (the pipe vibrates), or it damages the plastic pipe surface with a rigid inner surface.
Wrong size – too large: Common during improvised repairs or when the plumber doesn't have the correct size on hand. The pipe "moves" in the clamp and over time abrasion accumulates at the contact point and tilting occurs during temperature changes.
Too dense or too sparse fixing: Too dense – the sliding effect of the clamp is lost, the pipe cannot expand freely. Too sparse – the pipe bends, makes noise, and at long sections excessive stress on the joints occurs.
Over-tightening the screw in soft material: During installation into cheap plastic anchors in porous brick, over-tightening the screw causes the anchor to rotate instead of the clamp. Result – the clamp is not secure and eventually falls out.
Ignoring slope in horizontal routing: Clamps installed in a horizontal line without slope do not allow for drainage and in case of failure do not allow complete emptying of the pipe. This is not a direct clamp error, but an installation mistake that fixes the clamps in a permanently unsuitable position.

More on solutions to typical problems can be found in the article Common problems with plastic clamps – cracking, loosening, incorrect size.

Maintenance and lifespan of clamps in the Hepworth system

Plastic clamps in the Hepworth system do not require regular maintenance during normal operation if installed correctly. Nevertheless, I recommend checking visible clamps during each major heating system inspection (typically during boiler replacement or during the summer shutdown) to verify:

Whether the clamp body is not cracked or broken (visible cracks)
Whether the screw is still tight and the clamp does not sit "on the edge" of the anchor
Whether the position of the pipe between clamps corresponds to the original installation – i.e., whether the pipe has not bent (which would indicate an insufficient number of clamps)
Whether the clamp sleeve shows visible signs of abrasion (which would indicate excessive pipe movement or an unsuitable clamp type)

The lifespan of plastic clamps under normal conditions (indoor environment, temperatures up to 80 °C) is 20–30 years, matching the lifespan of the plastic pipe itself. In more aggressive environments (condensing humidity, chemical vapors), I recommend inspection every 5 years.

Further tips on what to look for during regular inspections can be found in the article Maintenance and inspection of pipe clamps – what to watch for.

Simple vs. double clamp – summary for the Hepworth system

The decision between a simple and a double clamp mainly depends on the installation configuration. As a general rule:

If the pipe runs separately (only one distribution loop, one pipe) – always use a simple clamp (601004H, 601005H or 601006H depending on the size)
If two pipes run parallel in the same plane with an axial distance matching a double clamp – a double clamp (601007H or 601008H) is faster, more economical, and aesthetically cleaner
At direction changes, branches, and at wall entries, always use a simple clamp for each pipe individually – a double clamp is not applicable here

A deeper comparison of both types and a decision-making process can be found in the article Simple clamp vs. double clamp – when to use which and also in How to choose the right plastic clamp for pipe – simple vs. double.

Frequently asked questions (FAQ)

Can I use Hepworth plastic clamps on other types of plastic pipes (e.g. PPR or PE-RT)?

In most cases yes, if the outer diameter of the pipe matches the clamp size. Plastic clamps 601004H, 601005H and 601006H are designed for specific outer diameters – if your PPR or PE-RT material has the same outer diameter (which is common for 15 mm, 18 mm and 22 mm), the clamps are functionally compatible. Always verify the outer diameter of your specific pipe according to the manufacturer's technical sheet – in plastic systems, it can sometimes differ even with nominally the same dimensions.

What is the distance between two pipes in the double clamp 601007H and 601008H?

The axial distance between two pipes in a double clamp is determined by the manufacturer – it is typically 50 mm (sometimes 60 mm) between the axes of the pipes. Before purchasing a double clamp, measure the actual distance between the axes of your parallel pipes and compare it with the technical parameters of the clamp. If the distance does not match, it is better to use two separate simple clamps.

Is it possible to fix a Hepworth pipe rigidly (without axial movement) using a standard clamp?

No, this is not a function of standard plastic clamps 601004H–601008H. These clamps are sliding – they allow axial movement due to thermal expansion. Fixed anchor points (fixpoints) in the Hepworth system are realized by other means – special blocking sleeves, or by embedding the pipe in the structure. Attempting to fix the pipe rigidly with a standard clamp (e.g. by tightening the sleeve with a screw) leads to pipe damage and excessive stress on the joints during temperature changes.

I have a 22 mm Hepworth pipe, but only a 20 mm clamp was available in the store. Can I use it?

No, under no circumstances. A clamp with an internal diameter of 20 mm for a pipe with an external diameter of 22 mm simply does not fit – it cannot be mounted on the pipe, and if forced on, it would cause local mechanical damage to the pipe surface and excessive stress on the wall. Always use clamps designed for the specific external diameter of the pipe. For a 22 mm pipe, the correct choice is simple clamp 601006H.

How can I determine which clamp is suitable for my pipe if I don't know the external diameter?

The easiest way is to measure the external diameter with a caliper. If you don't have one, you can measure the pipe circumference with a string and calculate the diameter (D = circumference / π). Another option is to look for markings on the pipe – plastic Hepworth pipes have the dimension printed on the surface, for example "15×1,5" or "18×2,0", where the first number is the external diameter in millimeters. A more detailed dimensional overview can be found in the article What clamp diameter do I need – dimensional overview for 15 mm, 18 mm and other pipes.

Can clamps for the Hepworth system crack? How to prevent it?

Yes, plastic clamps can crack – most commonly due to excessive tightening of the mounting screw, installation at low temperatures (plastic materials are more brittle below 5 °C), or mechanical impact. To prevent cracking: follow the appropriate torque when tightening (the clamp should be secure, not overly compressed), install at room temperature, and do not place clamps in positions exposed to mechanical impacts. More on causes and solutions can be found in the article Common problems with plastic clamps – cracking, loosening, incorrect size.

Conclusion – why the correct selection of clamps is not a minor issue

Clamps and clamps in the Hepworth system are small components with relatively low cost compared to the overall value of the installation. Nevertheless, their correct selection and installation determine whether the heating system will be quiet, reliable, and low-maintenance for the entire 20–30 years of its lifespan, or whether you will be dealing with cracking, vibrations, and pipe loosening after the first season.

The key principles are simple: always verify the external diameter of the pipe and choose the corresponding clamp size, consider using double clamps for parallel runs, follow recommended spacing, and remember that plastic clamps are sliding fastenings designed to work with the thermal expansion of plastic pipes – not rigid fixings.

The complete range of Hepworth system fittings including all five types of brackets can be found on the plastic fittings page. If you are unsure about the selection, compare the outer diameter of your pipe with the parameters of individual brackets – and if you need advice, product descriptions and technical specifications are always listed directly with the product.

Do you have a question about this topic?

Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.