Installing PEX-AL-PEX pipe: bending, pressing and proper joints step by step

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Installing PEX-AL-PEX pipe: bending, pressing and proper joints step by step

PEX-AL-PEX pipe is today one of the most widely used materials for heating, underfloor heating and drinking water installations. The reason is the combination of the strength of the aluminium layer, the chemical resistance of polyethylene and relatively simple installation – if you know what you're doing. That second part is key. From on-the-job experience, I know that most water leaks or pressure loss problems don't arise from poor material, but from installation errors: an insufficiently or incorrectly pressed joint, pipe bent below the minimum radius, use of incompatible fittings, or simply skipping deburring. This article is a practical manual – not theory, but a real procedure you can use on every job.

If you're still considering the right diameter or comparing PEX-AL-PEX with other materials, we recommend first reading the related articles in our Knowledge Center: How to choose PEX-AL-PEX pipe: diameter, wall thickness and pressure parameters and PEX-AL-PEX vs. other pipe types: comparison with copper, plastic and PEX-B. Here we will focus exclusively on the installation itself.

What you'll need before starting installation

Good preparation saves time and material. Before every installation, prepare the following tools and aids:

Pipe cutter – exclusively for PEX-AL-PEX, not a regular plastic cutter. The blade must be sharp so the cut is perpendicular and clean without compressing the wall.
Deburring tool – for internal deburring, also calibrated for circular cross-section. Separate for each diameter.
Pressing tongs with jaws for the specific fitting series (Henco, PERT, Giacomini, etc.) and specific diameter – 16, 20, 26 or 32 mm. Note: jaws are not universal between manufacturers.
Bender – manual spring type (for smaller diameters up to 20 mm) or mechanical / hand-operated with a mandrel (for 20–32 mm).
Calibrating tool – used after every cut to check roundness.
Measuring tape and marker to mark the pressing position.
Pressure test pump – a hydrostatic test after installation is essential.

Important: the tools must be compatible with the fitting system you are using. For example, "press" series fittings with a TH profile or "M" contour require different jaws. Always check this before making the first press on the job – not after twenty joints.

Cutting the pipe: the foundation of everything

Every joint begins with a cut. And this is exactly where the first mistakes happen in practice. PEX-AL-PEX pipe must always be cut perpendicular to its axis – any deviation causes the seal in the fitting to press unevenly around the whole circumference, and the joint may eventually start to leak.

Never use regular plastic scissors or a hand saw for cutting. A proper PEX-AL-PEX cutter works on the principle of compression and cutting with a wheel – the result is a clean, straight cut without shavings. The blade needs to be replaced regularly: a dull blade compresses the edges, deforms the aluminium layer, and the resulting cut shape becomes elliptical instead of round.

Deburring and calibration must follow immediately after every cut. The deburring tool removes metal microchips from the aluminium layer, which could otherwise cause erosion during flow. Calibration returns the pipe to the correct round cross-section if slight compression occurred during cutting. For 16 and 20 mm diameters, this deformation is easy to overlook, but it will show up during pressure testing as seal displacement.

Bending PEX-AL-PEX pipe without kinking

The aluminium layer in PEX-AL-PEX is what allows the pipe to hold its shape after bending – a huge advantage over pure PEX. At the same time, it is also its weak point: if you bend too quickly, under too small a radius, or without the correct tool, the aluminium layer "breaks" – creating a so-called kink, which narrows the cross-section, increases hydraulic resistance, and can lead to cracking in the long term.

Minimum bending radius by diameter

As reference values for standard installation, the following applies (the topic is covered in more detail in a separate article Minimum bending radius of PEX-AL-PEX pipe and proper shaping technique without kinking):

DN 16 (16 × 2 mm): minimum bending radius ≥ 80 mm (5× outer diameter)
DN 20 (20 × 2 mm): minimum bending radius ≥ 100 mm (5× outer diameter)
DN 26 (26 × 3 mm): minimum bending radius ≥ 130 mm (5× outer diameter)
DN 32 (32 × 3 mm): minimum bending radius ≥ 160 mm (5× outer diameter)

In practice, these values are considered an absolute minimum – for standard installations, it's wise to work with a larger radius whenever space allows. Sealing of piping where the pipe is bent right at the limit is always riskier, and if a fitting needs to be removed later, the bent section is much harder to handle.

Manual bending with a spring bender

For 16 and 20 mm diameters, a manual spring bender (the so-called spring) is sufficient. The spring is slipped over the pipe – not into it – and the tool prevents flattening during bending. Procedure: slide the spring onto the bending point, bend the pipe with a slow, smooth motion, not a jerky one. After removing the spring, check the bend by looking along the axis – there must be no visible flattening or kink on the inner side of the bend.

Mechanical bender with mandrel

For 26 and 32 mm diameters, a spring is not sufficient. Here a mechanical bender with a mandrel is needed, which supports the pipe from the inside during bending. Some models are lever-operated (manual), others are designed to be mounted on a stand. Without this tool, bending larger diameters is almost always associated with the risk of kinking, so it's better not to rely on it.

Joint systems: press-fit and screw-type compression fittings

There are two main systems for joining PEX-AL-PEX pipe, each with its own application and advantages:

1. Press-fit system

The press-fit system is currently the standard for professional installation of heating systems and water piping. Basically, it works so that a fitting with an olive (ring) is inserted into the pipe and the outer sleeve is compressed with pressing tongs – plastically deformed – into a precisely defined shape, creating a permanent, immovable joint with no possibility of disassembly without cutting.

Advantages of the press-fit system:

Speed – with a bit of practice, one joint takes less than 30 seconds
Repeatability – if the procedure is correct, the joints are identical
Pressure resistance – reaching 16 bar at 20 °C, 10 bar at 60 °C
No sealing compound, no thread – minimal maintenance

Disadvantages: you need pressing tongs (an investment or rental), the joint is permanent, and every fitting manufacturer requires its own specific jaws. Never mix jaws from different manufacturers with fittings from another manufacturer – the pressing profile differs, and the resulting joint will not seal correctly, even if it looks fine at first glance.

2. Compression (screw) system

The compression system uses a mechanical nut that is tightened with a wrench. The inner olive is pressed into the pipe wall, and the outer nut presses and seals the joint. The advantage is that it can be disassembled and requires no special tools. The disadvantage is that the joint requires tightness checks – especially in the first year of operation, temperature changes can cause slight loosening of the nuts. Compression joints are also generally more susceptible to vibration.

Compression fittings are suitable, for example, for inspection points requiring access, or for simpler cold water piping. For heating pipework with temperature cycling, we recommend the press-fit system whenever possible.

Step by step: how to correctly make a press-fit joint

Below is a detailed description of the entire procedure, the kind you would get from an experienced installer on your first job. Each step has its purpose, and skipping even one of them can lead to problems:

Step 1: Measuring and cutting

Measure the required pipe length, taking into account the insertion depth into the fitting (each fitting manufacturer states this in the technical documentation, typically 15–25 mm depending on diameter). Mark the length with a marker, firmly secure the pipe, and cut it with the cutter using one smooth rotating motion. Gradually close the blade without excessive pressure – pressure causes cross-section deformation.

Step 2: Deburring and calibration

Insert the deburring tool into the pipe and rotate it 2–3 times. The goal is: 1) to remove metal shavings from the aluminium layer, 2) to chamfer the inner edge so the fitting slides in more easily, 3) at the same time the outer jaw of the deburring tool chamfers the outer edge. After deburring, use the calibrating tool (a cylindrical tool matching the outer diameter), press it into the end of the pipe and rotate – this restores the cross-section to a round shape.

Step 3: Sliding on the sleeve

Slide the press sleeve (ring) onto the pipe – before anything else. This is the most common beginner's mistake: forgetting to slide on the sleeve before inserting the fitting, requiring the whole procedure to be repeated. The sleeve is always slid on towards the cut end (open side facing the cut).

Step 4: Inserting the fitting to the stop

Insert the fitting into the pipe with even pressure all the way to the stop – you must feel, or in the case of larger diameters hear, a "click" or firm resistance. Most fittings have an inspection window or visual marking to check the correct insertion depth. Do not skip this check before pressing – the pressing tongs cannot on their own fix a fitting that has not been fully inserted.

Step 5: Sliding the sleeve and pressing

Slide the sleeve onto the fitting (up to the stop ring) and fit the pressing tongs with the correct jaws. Squeeze the tongs to a full stroke – most quality tongs have a mechanism that prevents opening before the stroke is fully completed. This is a safeguard against an insufficiently pressed joint. After pressing, visually inspect the pressed area – it must be evenly shaped around the entire circumference, without flattening on one side.

Choosing the right diameter and product for your application

For choosing the right diameter, we also recommend reading the article in our Knowledge Center What diameter of PEX-AL-PEX pipe do I need for underfloor heating, radiators or water piping. Here we'll just briefly summarize which products cover common situations:

For underfloor heating, the absolute standard is PEX-AL-PEX pipe 16 × 2 for heating, underfloor heating and water. This diameter allows sufficient flow for typical circuit lengths (up to 100 m) and bends well into the underfloor heating spacing. The aluminium layer also significantly reduces oxygen diffusion into the medium, which is important for protecting the boiler's steel components.

For connecting radiators or a manifold branch where higher flow is needed, PEX-AL-PEX pipe 20 × 2 for heating, underfloor heating and water is suitable. The 16 mm internal diameter allows multiple radiators to be fed from a single circuit without excessive pressure drop.

For main horizontal piping or connecting a larger number of branches, the standard is PEX-AL-PEX pipe 26 × 3 for heating, underfloor heating and water – the 3 mm wall thickness guarantees significantly better mechanical properties and wear resistance in places where the pipe passes through structural elements.

For riser pipes or larger-diameter storage tank circuits, PEX-AL-PEX pipe 32 × 3 for heating, underfloor heating and water is intended. Here, a mechanical bender with a mandrel is already essential.

For jobs where an established brand and long history in Slovak installations matters, we also recommend VERME PE-AL-PEX pipe 16 × 2 for heating, underfloor heating and water – this product has identical dimensions and the same installation process, plus a long warranty period and good availability of replacement fittings.

Pipe routing, thermal expansion compensation and support

PEX-AL-PEX has a thermal expansion coefficient of approximately 0.025 mm/(m·K). For a 10 m long run with a temperature change of 50 °C (typical for a heating system), this means an expansion of about 12.5 mm. At first glance negligible, but with rigid anchoring in both directions and no compensation, this force can cause clamps to crack, the pipe to deform, or joints to loosen.

Practical guidance for routing pipe in shafts or under plaster:

Use a clamp every 0.5 m – for 16 and 20 mm diameters
For larger diameters, every 0.8–1.0 m
Never fix the pipe rigidly at both ends without a "moving point" – at least one clamp must be sliding
For long straight sections (over 6–8 m), install an expansion loop or make use of natural changes in the direction of the run
Where the pipe passes through walls and ceilings, use a protective sleeve (conduit) with loose fit

For pipes routed in a concrete screed (typically underfloor heating), the expansion is compensated by the free positioning within the screed itself – the pipe must not be laid directly on the thermal insulation without the ability to move. The edges of every room and floor expansion joints must be separated with an expansion strip, through which the pipe passes inside a protective sleeve.

Pressure test (hydrostatic): when, how and what to test

No PEX-AL-PEX installation may be covered, plastered, or embedded in screed without a preceding successful pressure test. This is a mandatory procedure according to standards and manufacturers' instructions, but also just common sense – finding a leak under a solid floor is many times more costly than performing a test before laying the flooring.

Pressure test procedure for PEX-AL-PEX heating pipework:

Fill the system with water and bleed the air – every highest point must be vented before the test.
Test pressure = 1.5 times the maximum operating pressure, but at least 6 bar. For standard low-temperature heating, this means testing at 6–9 bar.
Maintain the pressure for at least 30 minutes (according to EN 806-4, up to 2 hours for cold water).
A pressure drop of up to 0.2 bar over 30 minutes is considered acceptable (a slight expansion of the hoses occurs).
A larger drop or visible leak = the test failed, and the joint needs to be repaired.

Important: for press-fit joints, visual inspection after the pressure test is easier – a wet or damp spot will reveal the problem. For compression joints, also check that the nuts are properly tightened.

Most common mistakes when installing PEX-AL-PEX in practice

Based on service experience, we've compiled a list of mistakes encountered during complaints or inspections of existing installations. They are described in more detail in a separate article Common mistakes when installing PEX-AL-PEX pipe and how to avoid them; here is just a brief summary:

Skipping deburring and calibration – shavings damage the seal, a non-circular cross-section causes leaks.
Fitting not inserted to the stop – the seal is not in the correct position, the joint can fail under pressure or heat.
Incompatible jaws – the resulting pressing profile is incorrect, the joint appears tight but leaks under load.
Mixing different systems (fitting manufacturers) – each system has different tolerances, olives from other manufacturers do not press predictably.
Kinking the pipe when bending – narrowed cross-section, localized material fatigue, risk of cracking in the aluminium.
Pressure test skipped or insufficient – problems only appear after the screed is poured or plastering is done.
Missing expansion compensation – after a season, joints start loosening, clamps break, or plasterboard structures deform.

Special situations: installation in the floor, in chases and behind furniture

Underfloor heating: the pipe must lie freely on the thermal insulation (not under tension), fastened with clips or rails at the planned spacing (typically 10–20 cm depending on the circuit – more in the article PEX-AL-PEX pipe for underfloor heating: spacing, circuit length and maximum temperature). Joints must NEVER be under the screed – the entire circuit must always be a single continuous piece, without any joint in the heated zone. Fittings are only permitted at the manifold, which is accessible.

Routing in chases (wall channels): the chase must be wide enough for free movement of the pipe (internal chase width min. 1.5× the outer pipe diameter). The pipe must not be under tension inside the chase. Before plastering, a foam insulation sleeve is applied, which reduces heat loss and allows movement.

Behind furniture or in pre-wall installations: for these locations, a system with a long connecting pipe without joints is suitable, with fittings only at visible and accessible points. Combining PE-AL-PEX pipe with swivel or ball fittings also allows installation in tight spaces without cutting on site.

Frequently Asked Questions (FAQ)

Can I connect PEX-AL-PEX pipe directly to copper pipe?

Yes, a copper–PEX-AL-PEX joint is possible using transition fittings (reducers), which have a press or compression system on one side for PEX-AL-PEX, and a thread or press profile for copper on the other. Watch the flow direction: according to installation association guidelines, galvanized material should always be upstream of copper in the flow direction – for PEX-AL-PEX this is not a critical condition, but it is recommended that the aluminium material not be in galvanic contact with copper in the presence of moisture without a protective element.

How many times can I bend PEX-AL-PEX pipe at the same spot?

Technically more than once, but in practice you should carefully plan each bend right away. Repeated bending and straightening at the same spot fatigues the aluminium layer – after 3–5 bends at the same spot, microcracks form that are not visible but significantly weaken the pipe at that point. If you need to change the angle, cut the section and use a fitting – this is a better solution than "shaping on the fly".

Is it possible to repair cracked or damaged PEX-AL-PEX pipe without replacing the entire section?

Yes, the damaged section is cut out and replaced with a coupling fitting or a short inserted section with two fittings. For a patch on a pipe under screed, the repair must be visually accessible – meaning you have to cut an access opening in the floor, repair the joint, perform a pressure test, and then re-embed the patch in the screed. The procedure is described in more detail in the article Common faults and leaks in PEX-AL-PEX pipe: causes and repair.

How long does PEX-AL-PEX pipe last under normal operation?

Correctly installed and operated PEX-AL-PEX pipe has a manufacturer-guaranteed service life of typically 50 years at pressures up to 6 bar and temperatures up to 60 °C. Under temperature cycling (heating systems) and maximum values of 95 °C / 10 bar, the guaranteed horizon is 25–30 years. In practice, installations from the 1990s are still functional without replacement if they were properly laid and the joints were correctly pressed. Fittings or valves are usually replaced much sooner – the pipe itself, when well installed, is the most durable part of the system.

Can I use pressing tongs from another manufacturer if the jaw diameter is the same?

No. This is one of the most common mistakes. Every fitting manufacturer has a specific pressing contour profile – TH profile (the most widespread), M profile, U profile, and others. Even if the jaws physically fit onto the sleeve, the resulting shape and depth of pressing may differ, causing incorrect sealing. Always use the jaws recommended by the fitting manufacturer for the given system and diameter. Many fitting manufacturers even mark jaws with serial numbers that match the joint certification number.

Do I need to tighten the nuts on compression fittings after the first heating season?

It is recommended. After the first heating season, PEX-AL-PEX pipe goes through a heat–cool cycle, which causes a slight change in the dimensions of the sealing elements. For compression (screw) fittings, it is good practice to check the nut tightness after the first season – typically requiring a tightening of 1/8 to 1/4 turn. This step does not apply to pressed joints, which are permanent and do not change geometry after pressing.

Conclusion: installation is not the place to save time

PEX-AL-PEX is a great material that can last for decades without problems – but only when every joint is made according to the rules. Cutting, deburring, calibration, insertion to the stop, pressing with the correct jaws, and a final pressure test – these are not optional steps but a necessary sequence, where each step depends on the previous one. From experience, we know that an installer who has automated these steps works just as fast as one who skips some of them – but the result of their work lasts many times longer without needing a service callout.

If you're dealing with specific situations – special dimensions, non-standard applications, or compatibility questions – we also recommend checking out another article in our Knowledge Center: Frequently asked questions about PEX-AL-PEX pipe, which collects answers to technical questions from practice, as well as Maintenance and inspection of PEX-AL-PEX piping: what to regularly monitor for those who want to ensure the long service life of an existing installation.

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