How to choose the right plastic pipe clamp – single vs. double

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How to choose the right plastic pipe clamp – single vs. double

At first glance, a pipe clamp seems to be a trivial matter. And yet, customers often underestimate it more than any other component of the installation. When a technician arrives at a service call and sees a pipe hanging on four clamps instead of twelve, or sees a pipe secured with single clamps where double ones should have been used, they know complications are ahead. The pipe bends, makes noises when expanding, and sometimes mechanical stress on the joints occurs. And when you then ask the investor why he allowed it to be done this way, he will reply: "Well, I bought what the store told me." But the store only told him the required diameter, and that was it.

This article aims to provide a comprehensive overview of the topic – from the basic difference between a single and a double clamp, through dimensions and materials, to specific practical situations when to choose which variant. We will be talking about plastic clamps for the Hepworth system, i.e., clamps intended for plastic (PE-X, PP-R, PE-RT) and multi-layer pipes, which are used in heating and hot water distribution systems in large numbers today.

What is a pipe clamp (anchor) and what do we expect from it

A pipe clamp – in the terminology of the Hepworth system called an anchor – performs several tasks at once, even though it looks like a simple plastic clip from the outside. First, it holds the pipe in place and prevents it from moving on its own. Second, it absorbs or controls thermal expansion – i.e., the stretching and shrinking of the pipe with temperature changes. Third, it protects the pipe from vibrations and mechanical stress from the surrounding environment. And fourth, which is often underestimated, it contributes to the visual order of the installation – proper routing of the pipes is often a mandatory requirement in commercial spaces and technical rooms.

With plastic pipes, thermal expansion is significantly greater than with metal. A PP-R pipe will stretch by approximately 0.15 mm per meter of length when the temperature rises by 50 °C – on a 10-meter section, this is 1.5 mm. PE-X is similar. That sounds little, but on long straight sections without properly designed fixed and sliding points, expansion can cause deformation of the entire system. A clamp is therefore not just "a clip that holds the pipe" – it is an important element in the system for controlling pipe movement.

Therefore, the basic rule applies: clamps are always designed within the system, not as random anchoring. Every straight section of pipe requires fixed points (where the pipe must not move) and sliding points (where the pipe can move along the axis). For detailed instructions on how to correctly place clamps, see the article Spacing of pipe clamps – how to correctly place the anchoring.

Single anchor – when is it the right choice

A single anchor is a clamp that secures one pipe. The shape is typically a U-clip or a saddle with a crossbar, which closes after inserting the pipe – either with a spring-loaded catch or by a simple snap. It is mounted with one screw (or with a punch pin into a wall, ceiling or load-bearing structure).

In practice, you reach for it whenever:

the route carries only one pipe (e.g., a branch to one radiator, a supply to a water heater, a drain pipe)
there is enough space for each pipe separately and it does not matter to minimize the number of anchoring points
the pipes go in different directions and there is no reason to bundle them
it is a mounting on a structure where individual anchoring is suitable (e.g., lathing, wooden board, drywall with a punch pin)
you want to be able to dismantle or replace one pipe without affecting the other

A typical example from practice is a distribution in an apartment building, where each bathroom has its own cold and hot pipe, but each runs separately along the wall. Here, a single anchor makes full sense – each pipe is held by its own clamp, the installation is clean and symmetrical.

For the Hepworth system, for example, there are Single anchor 601004H, Single anchor 601005H and Single anchor 601006H available, each corresponding to a different pipe diameter. Choosing the correct size is critical – a clamp that is too loose cannot properly control expansion, and a clamp that is too tight cannot be properly closed and may damage the pipe surface.

Dual Clamp – When and Why to Prefer It

A dual clamp is structurally designed to secure two parallel pipes at one anchoring point (one screw or wall anchor) at the same time. Both pipes are firmly placed side by side in one body of the clamp, maintaining a defined axial distance between them and making the whole system more stable and compact.

A dual clamp is the right choice in situations where:

you are running two parallel pipes of the same or similar diameter (typically heating supply and return, or cold and hot water)
you want to minimize the number of anchoring points and thus save time during installation as well as materials (anchors, screws)
the uniform and aesthetically clean appearance of the installation is important (technical room, visible installation in an administrative building)
the pipes run in the same direction for a long section without branches
you are working in a confined installation shaft or pipe channel where space is limited

From an economic perspective, a dual clamp is particularly interesting for larger projects. For example, if you have a 30-meter heating supply and return line that requires anchoring points every 1.2 meters, you are talking about 25 anchoring points. Individual single clamps would mean 50 holes in the wall, 50 anchors and 50 screws. Dual clamps reduce this to 25 holes, 25 anchors and 25 screws – with the same technical effect. And the installation is 40 percent faster.

The Hepworth system offers, for example, Dual Clamp 601007H and Dual Clamp 601008H for these situations – both are designed to securely hold both pipes and maintain a constant axial distance between them when the correct size is used.

Size Overview – Why Diameter Matters More Than You Think

This is where amateurs most often make a mistake. A clamp for a 16 mm pipe does not look dramatically different from a clamp for a 20 mm pipe at first glance. But functionally, the difference is crucial. The pipe must fit into the clamp with a defined clearance – at a sliding point, it must be able to move axially, but must not be free to move radially. At a fixed point, it must be properly secured. A clamp that is too large will not secure either, and a clamp that is too small cannot be closed or may press against the pipe.

Common diameters of plastic pipes in heating and water supply systems:

15 mm – typically PE-X or multi-layer pipes for underfloor heating and thin pipe runs
18 mm – a less common size, but used by some manufacturers
20 mm – a very common diameter for PP-R and PE-X lines for hot and cold water
25 mm – vertical pipe, connection between boiler and storage tank, main line
32 mm – primary circuit, connections in the technical room

Important: the outer diameter of a plastic pipe is not the same as the nominal dimension in inches, which you are used to working with in copper or steel pipe systems. A PP-R pipe DN 20 has an outer diameter of 20 mm, but a copper pipe with a nominal size of 3/4" has an outer diameter of 22 mm. This confusion is a source of many incompatibilities. If you are unsure, read the article What Size Clamp Do I Need – Size Overview for 15 mm, 18 mm and Other Pipes, where you will find a detailed table.

Material and Long-Term Durability of Plastic Clamps

Clamps for the Hepworth system are made of high-quality polypropylene or polyamide, depending on the specific model. Both materials have long-term resistance to hot water, moisture and common chemicals. A disadvantage of plastic clamps compared to metal ones is lower strength at extreme temperatures and after long-term exposure to UV radiation (which is usually not a problem in internal pipe systems).

Plastic clamps are also electrically non-conductive, which is an advantage wherever galvanic corrosion may occur due to the combination of different metal materials. When transitioning from plastic pipe to metal pipe (e.g., a steel radiator, a copper manifold), a plastic clamp does not create an electrical contact between the materials and therefore does not contribute to accelerated corrosion. More about the comparison with metal clamps can be found in the article Plastic vs. Metal Clamps for Pipes – Advantages, Disadvantages and Appropriate Use.

Regarding thermal limits: standard plastic clamps for heating are dimensioned for a continuous operating temperature up to 95 °C and short-term temperature peaks up to 110 °C. In underfloor heating, where the temperature in the heating circuit does not exceed 45–55 °C, plastic clamps are absolutely sufficient and in practice will last for decades without any problems.

Installation Procedures and Common Installation Mistakes

Correct installation of a clamp is a quick operation, but mistakes can still be made here, which may only become apparent after years. Basic rules:

Do not tighten screws to maximum at sliding points. A sliding clamp must allow axial movement of the pipe. If you over-tighten the screw and the clamp clamps the pipe too tightly, expansion has nowhere to go – the pipe will bulge or the joint will crack. At a sliding point, tighten the screw just enough to keep the clamp stable, but allow the pipe to move freely within it.
On the other hand, tighten the screw properly at fixed points. A fixed point must secure the pipe so that it does not move either axially or radially. If the fixed point is loose, expansion will shift elsewhere and the system will operate in an uncontrolled manner.
Observe the spacing. For horizontal plastic pipe runs, a general rule is that the spacing between clamps should not be greater than 10–12 times the outer diameter of the pipe. For a 20 mm pipe, this means a clamp every 20–24 cm when the medium is hot (plastic pipes soften at high temperatures and may bend).
Never anchor the pipe directly to the surface without a distance profile in places where it crosses a divided structure (e.g., ceiling penetration). The pipe must have room to move in this location as well.
Install a dual clamp always perpendicular to the axis of the pipe. If the clamp is tilted, one pipe is extended forward and the other backward – the clamp then holds the pipes asymmetrically and during expansion, uneven stress occurs.

A detailed step-by-step procedure can be found in the article Installation of plastic pipe clamps step by step, where the entire process is illustrated, including the selection of the correct anchor for different types of substrates.

Compatibility of clamps with the Hepworth pipe system

Anchors of the 601xxxH series are specifically designed for the Hepworth pipe system, but in practice, they are compatible with most plastic pipes of the same outer diameter from various manufacturers. What matters is the outer diameter – not the brand of the pipe.

Important note for multi-layer pipes (PE-AL-PE or PE-AL-PE-X): multi-layer pipes have the same outer diameter as PP-R or PE-X pipes of the same nominal size, so the clamps are interchangeable. The difference is in stiffness – multi-layer pipes are stiffer and bend less, so you can slightly increase the spacing between clamps (but only by 10–15 %, not more).

The Hepworth system is designed as a complete solution from clamps through fittings to anchoring at structural transitions. For more information on the compatibility of the entire system, you can read the article Clamps for the Hepworth system – compatibility with plastic piping.

Practical scenarios from installation practice

Scenario 1: Single-family house, bathroom and WC on the upper floor

On the upper floor, two parallel lines – cold water and hot water from a central tank – run along the wall. Both lines are made of 20 mm PE-X pipe. The route is 8 meters long, straight, without branches. Solution: double clamps every 25–30 cm along the entire route. One anchoring point secures both pipes at once, installation takes less time, the wall has fewer holes, and the result is visually clean. Fixed points are placed at both ends of the bend/connection (fittings) and once in the middle of the section. The remaining clamps are sliding.

Scenario 2: Technical room, heating distribution

In the technical room, three heating circuits run from the boiler – each has a supply and return. That is six PP-R 25 mm pipes in total. Each circuit runs in a different direction. Here, a double clamp makes sense for each pair of supply-return, but each pair has a different route, so they cannot be combined. Result: three pairs of double clamps on three different routes. In addition to saving drilling, this also has an operational benefit – in the case of a fault in one circuit, the technician clearly sees which pipes belong together.

Scenario 3: Floor heating, manifold

Five PE-X 16 mm circuits run out from the floor manifold (collector), each heading in a different direction. Here, the pipes diverge and curve in different directions – a double clamp does not make sense, because the pipes diverge after a few centimeters. Here, the right choice is simple clamps for each pipe separately, or a special manifold bracket. The distance between clamps on the straight section should be no more than 15 cm for PE-X 16 mm at a medium temperature of 45 °C in horizontal routing.

Scenario 4: Installation shaft in an apartment building

A narrow installation shaft where apartment supply lines for hot water, cold water, circulation, and heating return are squeezed together – four pipes of different diameters (20 and 25 mm). Space is limited and access to the wall is difficult. The solution is a combination: a pair of hot/cold water in a double clamp, circulation and heating separately with simple clamps screwed into the adjacent wall of the shaft. Each clamp is selected so that it can be installed without the need to access adjacent pipes.

What to pay attention to when purchasing – most common mistakes

The following mistakes repeatedly occur in practice when ordering clamps:

Mixing up internal and external diameter: the customer orders a clamp based on the internal diameter of the pipe, but the clamp is dimensioned according to the external diameter. Result: the clamp is too large.
Clamp for copper pipe instead of plastic: copper 22 mm vs. plastic 20 mm – the dimensions are similar, but not the same. A clamp for 22 mm copper pipe will be loose on a 20 mm plastic pipe.
Ordering only single clamps instead of double ones: the customer sees a cheaper single clamp in the catalog, orders twice as many pieces – but forgets that they also have to drill and anchor twice as many. The total time and cost are higher.
Ignoring spacing requirements: the customer buys fewer clamps than needed, the pipe sags between clamps, and at high medium temperatures, visible deformation occurs.
Inappropriate clamp for a sliding point: the customer uses a fixed clamp (with a securing bracket) at a sliding point, the pipe has no room to expand.

For more information on typical mistakes and their consequences, you can read the article Common problems with plastic clamps – cracking, loosening, inappropriate size.

Price and economics – is it worth saving on clamps?

Clamps are a cheap item compared to pipes, fittings, and labor. Precisely because of this, people tend to save money in the wrong way – not by choosing a cheaper manufacturer, but by buying fewer pieces than needed. This is a mistake. The price of one clamp is in single-digit euros. Repairing a broken connection due to insufficiently supported piping can cost hundreds of euros, plus the cost of shutting down the system, draining it, and drying the walls. The ratio is clear.

On the other hand, it is possible to save money sensibly by choosing double clamps where it makes sense – reducing the number of anchoring points and thus the number of anchors, screws, and wall holes. And the technician's time is an important factor in long-term rental or contract work.

Maintenance and long-term inspection of pipe clamps

Plastic clamps do not require regular maintenance in the sense of greasing or galvanizing. Nevertheless, during each inspection of the heating system (ideally every 2–3 years), the technician should visually inspect the condition of the clamps. What to look for:

cracks or white spots on the plastic body of the clamp (a sign of fatigue stress or incorrect size)
loose screws (a common occurrence after several expansion seasons – simply tighten the screw)
clamps where the pipe slips out of the groove (either incorrect size or the sliding point was forcibly moved sideways)
pipe deformation at the clamp location (the clamp was too small and pressed against the pipe)

For more information on proper maintenance and inspection of pipe runs, read the article Maintenance and inspection of pipe clamps – what to watch out for.

Summary – decision criteria at a glance

If you are unsure which clamp to choose, go through this simplified decision tree:

Are you running a single pipe? → Simple clamp.
Are you running two pipes in parallel, in the same direction, over a long section? → Double clamp.
Are you running two pipes, but they diverge after a while? → Simple clamps for each one separately.
Do you want to minimize drilling in the wall and speed up installation? → Double clamp whenever the route geometry allows.
Is it a sliding or fixed point? → Sliding: clamp loosely tightened; fixed: clamp tightly tightened or a special solution for a fixed point.

A complete comparison of both types is also available in the separate article Simple clamp vs. double clamp – when to use which, where both types are compared in a table according to various criteria.

Frequently asked questions (FAQ)

Can I use a double clamp for two pipes of different diameters?

Most double clamps in the Hepworth system are designed for two pipes of the same diameter. If you have two pipes of different diameters (e.g., 20 mm and 25 mm) running in parallel, use two simple clamps side by side. There are also special adjustable solutions, but with the Hepworth system, it is simpler and more reliable to stick to one diameter for the double clamp.

What is the recommended spacing of clamps for horizontal installation of plastic pipe DN 20?

For hot media (45–80 °C), the recommended spacing of clamps is a maximum of 20–25 cm for PE-X and PP-R pipes DN 20 in horizontal installation. For cold water, you can go up to 30–35 cm. In vertical installation, you can increase the spacing by 20–30 %, as a pipe hanging vertically has less tendency to bend under its own weight.

What is the difference between clamps 601007H and 601008H?

Both are double clamps in the Hepworth system; the difference is in the dimensions – each is intended for a different pipe outer diameter. Double clamp 601007H and Double clamp 601008H differ in the size of the seat. Always verify the outer diameter of your pipe and compare it with the technical data of the respective clamp model before ordering.

Is it possible to reuse a plastic clamp after pipe disassembly?

Yes, plastic clamps in the Hepworth system are designed to be opened, the pipe removed, and the clamp reused – provided there is no mechanical damage or cracking of the plastic body. In practice, clamps are commonly reused during renovations if they are visually in good condition and no cracking sounds are heard when opening. If there is any suspicion of material fatigue, it is better to replace the clamp – the cost of a clamp is negligible compared to the risk.

Can I use Hepworth clamps on copper or steel pipes?

Technically yes – if the outer diameter of the copper or steel pipe matches the clamp size. However, you should consider that plastic clamps are dimensioned for temperatures up to 95 °C and do not account for the weight of water-filled metal pipes as metal clamps do. For heavy metal pipe runs (e.g., thick-walled steel DN 32 and larger), metal clamps with higher load capacity are more suitable.

What happens if I install a clamp one size larger than needed?

The clamp will be loose in the radial direction on the pipe. This means the pipe can move sideways, will not be able to perform the function of a fixed point, and during expansion will also shift where it should remain fixed. In the case of a sliding point, this may be acceptable, but only if the pipe at least stays in the seat and does not slip out. In general: do not use a larger clamp as a substitute for the correct size; always choose the size corresponding to the outer diameter of the pipe.

Conclusion

Choosing between a simple and a double clamp is neither complicated nor trivial – it is a matter of the specific situation in a specific installation. A simple clamp makes sense wherever a single pipe is running or where pipe routes diverge. A double clamp is more efficient and practical wherever two pipes run parallel for a long distance. Combining both types in one installation is common and correct. The decisive factors are always the outer diameter of the pipe, the correct distinction between fixed and sliding points, and compliance with recommended spacing.

Products of plastic clamps and fasteners for the Hepworth system are available in the full range at atria.sk, where you can compare individual models by dimension and type (simple / double).

Do you have a question about this topic?

Are you unsure or dealing with a specific situation in your home? Write to us – we are happy to help.