Step-by-step installation of PEX and multilayer piping

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Why proper installation of PEX and multilayer pipe is key

The pipe itself is only half of the success of any heating or plumbing installation. Even the highest quality PEX or multilayer (PEX-AL-PEX) pipe can cause serious problems if installed using the wrong procedure, inappropriate tools, or without following the manufacturer's technological instructions. Over twenty years of experience in the field has repeatedly confirmed one rule - the vast majority of leak complaints do not arise from material defects, but from installation errors. Improperly insulated cut, forgotten calibration, exceeded bending radius, insufficiently tightened nut, or a poorly performed pressure test - these are the causes of nine out of ten cases where a leaking joint appears in the floor or wall after years of operation.

This article is a practical guide to installation, following up on theoretical topics such as PEX vs multilayer pipe - differences and usage or What pressure and temperature can PEX pipe withstand (PN6, PN10). If you are still choosing the right type and diameter of pipe, we recommend first reading the articles How to choose pipe for heating, water or floor heating and What pipe diameter do I need according to the type of layout. Here we will focus exclusively on how to physically install the pipe so that it lasts for decades without a single drop.

Difference between PEX and multilayer pipe from the installation point of view

Before moving on to the actual procedure, it is important to understand that PEX (cross-linked polyethylene, most commonly type PEX-A produced by the Engel method) and multilayer PEX-AL-PEX pipe are installed using similar tools and the same types of fittings, but they behave differently mechanically.

PEX pipe is flexible, has so-called shape memory (after bending, it tries to return to its original state) and can be expanded - this means that the end of the pipe can be temporarily stretched using an expander and a fitting can be pushed on without the need for crimping. Thanks to this, it is well suited for long straight sections and slight curves directly from the reel.
Multilayer PEX-AL-PEX pipe has an aluminum layer in the middle, which gives it the ability to hold the shape after bending (similar to copper pipe) and at the same time prevents oxygen diffusion through the pipe wall. It is not suitable for expansion, it is installed exclusively with crimping or screwing (Euroconus) fittings with an additional sleeve or ring.

This difference directly affects the choice of tools and the work procedure, so in the following chapters we distinguish where the procedure applies to both types and where it is specific.

Tools and accessories that must not be missing

Before the first cut, prepare a complete set of tools. Improvisation (cutting with a knife, calibration with a screwdriver) is the most common cause of leaky joints among DIY enthusiasts and inexperienced installers.

Plastic pipe cutters - special ones, with a sharp blade without teeth, to ensure a perpendicular and smooth cut. Common pliers or a saw will cause deformation and jamming of the fitting.
Calibration and chamfering tool (reamer) - a tool used to round the inner diameter of the pipe after cutting and slightly chamfer the outer edge (facing), so that the fitting or sleeve can be pushed on without scratching the sealing surfaces.
Expander (expanding head) - for systems with expanded PEX-A pipe. There are manual and battery-powered versions. The head must exactly match the pipe dimension (16, 17, 20, 25 mm...).
Crimping pliers with appropriate jaws - for press systems (crimp fittings with O-ring). The jaws must match the profile (TH, U, H according to the manufacturer) and the pipe dimension.
Torque wrench or standard box wrench - for screwing (Euroconus/compression) joints, where tightening is performed mechanically without crimping.
Bending spring (internal and external) - for bending the pipe without a fitting at the point of direction change, prevents kinking and flattening of the diameter.
Tape measure, marker, protractor for accurate placement of loops, especially in floor heating.
Pressure testing pump (manometer set) for pressure testing after installation is completed.

For larger projects (multiple apartments, a single-family house with floor heating on the entire area), it is worth investing in a battery-powered expander or crimping pliers - they save dozens of hours of work and ensure repeatable joint quality without dependence on the installer's strength and fatigue.

Preparation of the pipe before installation

Inspection and acclimatization

Always inspect the reel or rod of pipe before installation - the surface must not have longitudinal cracks, bubbles, or flattened areas. If the pipe was stored outside at low temperatures (below 5 °C), let it acclimatize for at least 2-3 hours in a warm room before processing. Cold PEX pipe is harder, harder to bend, and when forcibly straightened from the reel, there is a risk of microcracks forming, which may appear only after years of operation under pressure.

Unwinding from the reel

Always unwind the pipe by rotating the entire reel (placed flat or on an unwinding stand), never pull the pipe directly over the edge of a standing reel - this creates twisting loops that are difficult to straighten later and may break. For long sections (e.g., 200 m reel), it is reasonable to work in a pair or use an unwinding stand with a freely rotating axis.

Cutting to length

The cut must always be perpendicular to the pipe axis. A slanted cut will cause uneven seating of the sealing O-ring or incomplete contact with the fitting stem, which is a direct path to a leak. Use only cutters intended for this purpose, regularly check the blade and replace it if it becomes dull - a dull blade crushes the pipe rather than cuts it, which changes the diameter at the cut location.

Step-by-step installation procedure

The following procedure generally applies to both expansion and crimping systems, with noted differences where they differ.

Step 1 - measuring and cutting

Measure the required length with a 5-10 cm reserve for possible correction. Cut straight, in one smooth stroke without sawing.

Step 2 - calibration and chamfering

Insert the end of the pipe into the calibration/chamfering head and turn it several times to align the inner diameter and chamfer the outer edge. This step must not be skipped even in the case of a "quick fix" - it is precisely here that the most rushed mistakes occur.

Step 3a - expansion (PEX-A systems)

Insert the expansion head into the end of the pipe and press and rotate it several times (typically 6-10 times depending on the dimension and temperature) until the diameter is sufficiently stretched to push on the fitting with a ring. Immediately after expansion (while the material is still stretched), push the fitting all the way to the stop - PEX-A will, thanks to its shape memory, begin to contract back within a few seconds to minutes and tightly surround the fitting. At low ambient temperatures, the contraction takes longer, so leave the joint to "tighten" for at least 5-10 minutes before handling.

Step 3b - Pressing (press systems)

Slide a ring/casing onto the end of the pipe, then insert the fitting until it reaches the stop of the pipe, finally slide the ring into position above the sealing O-ring and crimp it using pliers with the appropriate jaws. Always check the inspection window on the fitting (if the type includes it) - it indicates whether the fitting has actually been pushed to the stop before pressing.

Step 3c - Screwing (Euroconus) connection

Slide a nut and a support sleeve (metal or plastic casing inserted inside the pipe) onto the pipe, then insert the pipe onto the conical neck of the fitting and tighten the nut with a wrench. This type of connection is removable, so it is suitable especially for manifolds and valves, where future maintenance is expected.

Step 4 - Visual and mechanical inspection

After connecting, check that the connection is coaxial, without lateral loading, and gently pull to verify that the fitting cannot be pulled out. For larger projects, it is advisable to photograph the connections before embedding them in the screed or before covering them in the groove - in case of a future complaint, photographic documentation is invaluable.

Bending the pipe and minimum bending radii

One of the advantages of PEX and multilayer pipe compared to copper is the possibility to bend it directly without a fitting at the place of direction change, which saves joints (and thus also potential leakage points). However, it is necessary to observe the minimum bending radius specified by the manufacturer in the technical data sheet - typically:

by hand (freehand): approximately 5 times the outer diameter of the pipe,
with a bending spring: approximately 3.5-4 times the outer diameter of the pipe.

For example, with the pipe PEX 20x2 mm, the minimum bending radius without a spring is about 100 mm, with an internal spring it can be reduced to approximately 70-80 mm. With a smaller dimension, such as PEX 17x2 mm, the minimum radius ranges from about 60-85 mm depending on whether a spring is used.

With multilayer pipe with an aluminum layer, the situation is different - the pipe is harder to bend, kinking (collapse) is a risk when the radius is exceeded, and since aluminum loses strength and tightness against diffusion after kinking, the kinked section must always be cut out and replaced with a new piece, it must never be "straightened back".

Installation of the pipe according to the type of distribution

Floor heating

With floor heating, the pipe is laid in a system board (foam board with thermal insulation) in one of two basic patterns - spiral (snail) or meander (snake). The spiral pattern ensures a more even temperature distribution across the surface, as the supply and return pipes alternate next to each other; the meander pattern is easier to lay, but with longer loops, a larger temperature difference between the inlet and outlet of the room occurs. The spacing of the pipe laying typically ranges between 10-30 cm depending on the room's heat loss and the required performance - in the peripheral zones near windows, it is laid more densely (10-15 cm), and in the center of the room more sparsely (20-30 cm).

The length of one loop should not usually exceed 100-120 m at a dimension of 17x2 mm, or slightly more at 20x2 mm from the perspective of pressure loss and uniformity - however, an exact calculation always belongs to the heating project, not to an estimate on the construction site.

Wall and ceiling distribution of heating and water

With distribution in grooves of masonry partitions or in cavity walls, the pipe is laid in a protective sleeve (corrugated or smooth tube), which allows expansion of the pipe due to temperature changes without the pipe rubbing against the plaster or concrete. The sleeve also serves as protection against mechanical damage during later construction work (e.g., drilling into the wall).

Distribution in the screed (floor supply to manifolds)

The supply pipe to manifolds, which runs across the floor outside the heating loops, is always laid in a sleeve to thermally and mechanically separate it from the surrounding screed and to allow replacement in case of failure without demolition.

Connectors, fittings and transitions to other materials

The choice of fitting is closely related to the type of pipe and the place of use. A detailed overview can be found in the article "Which connectors and fittings to use for PEX pipe", here we only summarize the most important practical points:

Press fittings - the most reliable and fastest for series installation, the connection is non-removable, suitable under the screed and in grooves.
Expansion fittings - exclusively for PEX-A pipe, the connection is created by shrinking the material, without the need for an O-ring in some systems (sealing is ensured by the material itself), extremely reliable when the correct procedure is followed.
Screwing (Euroconus) - removable, ideal for manifolds, valves, boilers - everywhere where future service intervention is expected.
Transition fittings to metal (brass, steel) - when connecting to existing steel or copper distribution, boiler, pump unit.

When selecting the size of the fitting, it must always exactly match the outer diameter and wall thickness of the pipe - for example, a fitting for 20x2 mm is not interchangeable with a fitting for 20x2.8 mm, even though the outer diameter is the same, because the inner diameter (and thus also the diameter after expansion or pressing) is different.

Pressure test - an essential step before covering

Regardless of how careful the installation procedure was, no installation should be covered (poured into the screed, embedded, or covered with drywall) without performing and documenting a pressure test. A common practice for water and heating distribution is as follows:

The system is filled with water and vented.
The pressure is increased to 1.3-1.5 times the maximum operating pressure (typically tested at 6 or 10 bar depending on the type of piping system).
The test usually lasts at least 30 minutes to check for pressure drop caused by leakage, and it is recommended to keep the system under pressure for several hours up to 24 hours to detect slow micro-leaks.
The result (pressure behavior over time) is recorded in a pressure test protocol, which is part of the handover documentation for the building.

With underfloor heating, it is also recommended to perform a so-called "hot" test just before pouring the screed (the system is heated to approximately 40-50 °C under pressure for several hours), because thermal expansion can reveal a joint that was tight during the cold test but slightly shifted when heated.

Common installation errors from practice

A detailed analysis can be found in the separate article "Common errors and problems during pipe installation." Here we list those that we encounter most frequently during the installation of PEX and multilayer piping:

Skipping calibration - the fitting slides on, but does not seat properly. The joint appears tight during the cold test, but after heating and pressure cycling, it starts to leak.
Insufficient time for contraction after expansion - the installer handles the pipe too soon, and the joint slightly loosens when bent or pulled before the material fully contracts.
Exceeded bend radius - causes a reduction in diameter (crease), increased hydraulic resistance, and in the worst case, pipe wall rupture, especially in multilayer pipes with an aluminum layer.
Missing protective sleeve in the partition or in the screed - leads to mechanical damage to the pipe during later work (drilling, anchoring) and prevents expansion.
Mixing incompatible fittings from different manufacturers - even if they fit dimensionally, sealing elements (O-rings, stem geometry) may differ enough that the joint is not reliable in the long term.
Installation without pressure testing before covering - the most expensive error, which only becomes apparent after the screed is poured or the pipe is embedded in the wall, when repairs require demolition.

Storage and handling before installation

The quality of installation starts with proper handling of the pipe on the construction site. Coils are stored horizontally, protected from direct sunlight (UV degradation of the surface) and from freezing below -5 °C during long-term storage. Rods are stored horizontally on a flat base to prevent warping. More detailed recommendations can be found in the article "Storage and handling of pipes in rods and coils" - here we just remind you that even short-term improper storage (e.g., a coil placed on an edge outside during winter) can degrade otherwise flawless material even before the first cut.

Practical examples

Example 1 - underfloor heating in an apartment of 75 m²

In an apartment with five rooms, a pipe of 17x2 mm diameter is commonly used, for example from the coil PEX 17x2 mm - 240 m, which with an average spacing of 15-20 cm covers most of a standard apartment without the need to purchase an additional coil. When implementing multiple apartments at once (e.g., in a developer's construction), it is cost-effective to order a larger coil such as PEX 17x2 mm - 600 m, which reduces the number of joints between coils and simplifies logistics on site.

Example 2 - risers and main piping in a single-family house

For main piping between the boiler room and distributors on individual floors, where higher flow capacity is required, a 25x2.3 mm diameter is commonly used, for example PEX 25x2.3 mm - 200 m. These lines are usually run in protective sleeves through the ceiling or in an installation shaft and are connected using crimp fittings with a transition to brass threaded connections to the distributor.

Example 3 - repair after drilling through a wall

A common scenario from service interventions: during the installation of a shelf in the bathroom, the pipe running in a groove without a protective sleeve was accidentally drilled through. Since the pipe was not protected, the PEX pipe was directly perforated and water leaked into the wall structure. The repair required cutting out a larger section of the tiling, replacing the damaged pipe section using two crimped joints, and performing a new pressure test before re-tiling. This case is a classic example of why a protective sleeve in a groove should never be skipped, even if it seems like an unnecessary additional cost at first glance.

When to call a professional and when you can manage on your own

Simpler sections (extension of the piping, replacement of a damaged section, connecting a new radiator to an existing system) can be handled by a skilled DIYer with the tools and procedures described above. However, for the complete design and implementation of underfloor heating in an entire house, hydraulic balancing of multiple circuits, or connecting to a heat pump, we strongly recommend entrusting the project and implementation to a professional company - an error in circuit dimensioning or hydraulic balancing is much harder to fix than an error in the pipe joint itself.

Frequently asked questions about PEX and multilayer pipe installation

Can PEX pipe be joined without special tools, using only threaded fittings?

Yes, threaded (Euroconus) fittings do not require a crimper or expander, only suitable wrenches to tighten the nut. They are slightly more expensive per joint and larger in size, so they are mainly used for connecting to distributors and valves, not as a widespread solution for dozens of joints in the floor.

How long after expansion must I wait before handling the pipe?

At room temperature (around 20 °C), the PEX-A material contracts back to its original diameter within a few minutes, usually within 5-10 minutes the joint is fully functional. At lower ambient temperatures (e.g., a winter construction site without heating), the time is extended, so it is recommended to wait at least 15-20 minutes before handling the joint, and in case of doubts, gently check the fitting by pulling.

Can I combine fittings from one manufacturer with pipe from another manufacturer?

Generally, this is not recommended. Although the nominal dimensions (e.g., 20x2 mm) appear to be compatible, the exact tolerances of the outer and inner diameters, material hardness, and sealing surface geometry vary slightly between manufacturers. Safe and guaranteed installation is always achieved with system components from the same manufacturer.

What is the difference between installation in a screed and in a wall groove in terms of pipe protection?

Heating circuits are usually laid directly in the system board without a protective sleeve in the screed (as the screed does not contain metal parts that could later damage the pipe), whereas all supply lines to distributors and all piping in masonry partitions or behind plaster are always run in protective sleeves due to the risk of future drilling or anchoring in the wall.

Is it necessary to let the pipe "breathe" after installation before pouring the screed?

Yes, it is recommended to keep the system filled and under pressure during the screed pouring (so that any damage during construction work is immediately indicated by a pressure drop) and to perform a hot test just before laying the final floor layer, as described in the section on pressure tests.

What to do if you are unsure whether the joint is still tight after years of operation?

If symptoms such as a damp spot on the ceiling, pressure drop in the system, or increased consumption of make-up water appear, it is usually a leak in the joint or pipe damage - a detailed diagnostic and solution procedure can be found in the article "Cracked or Leaking Pipes - Causes and Solutions."

Summary at the end

The installation of PEX and multilayer piping is not a complicated technology, but it is sensitive to thoroughness. A perpendicular cut, careful calibration, the correct choice of fitting type and size, adherence to the minimum bend radius, the use of protective sleeves wherever required, and finally a properly performed and documented pressure test - these are the five pillars on which a trouble-free installation stands for the next few decades. It is worth investing time in preparation and the right tools instead of later breaking up a finished floor or tiling due to a joint that should have been done properly the first time. When choosing the pipe itself, it is worth reaching for proven dimensions, such as PEX 20x2 mm for main lines, or smaller diameters for floor heating, and the full range of piping can be found in the category Pipes - Heating, Water, Floor.

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.