How to Choose the Right Heating Pipe: Copper, Multilayer or Plastic?

How to Choose the Right Heating Pipe: Copper, Multilayer or Plastic?

Choosing heating pipes is a decision that will affect the reliability, lifespan and maintenance demands of the entire heating system for decades to come. When a customer asks "what should I buy?", the answer is never simple – it depends on the heat source they have, the temperatures and pressures expected in the system, who will install it, what budget they have, and where the pipework will run. In practice, in Slovakia today we encounter three main categories: copper pipe, multilayer (PE-AL-PE / PE-RT-AL-PE-RT) pipe and pure plastic pipe (polybutylene, PPR or PE-RT). Each of these groups has its clear strengths, but also limitations that sellers and installers do not always talk about openly.

This article will help you understand the technical parameters, choose the right material for a specific application, and avoid mistakes we see repeatedly on jobs – from incorrectly chosen diameters, through unsuitable connections, to using plastic in places where a different material should have been used.

Three main material groups and their basic properties

Copper pipe

Copper is a classic in plumbing practice with more than a century of tradition. Copper pipes are manufactured in hard state (marked R250, so-called straight lengths) and in half-hard state (R220, wound into coils). For heating, the most commonly used diameters are 12×1, 15×1, 18×1, 22×1 and 28×1 mm (outer diameter × wall thickness). Copper has exceptional thermal conductivity (385 W/m·K), which makes it suitable for applications where heat passes directly through the pipe wall – typically with copper radiators, convectors, or installations in boiler rooms with short, high-temperature pipework.

The operating temperature for copper pipe in heating is usually up to 110 °C, and even higher with special alloys. The maximum working pressure for common wall thicknesses and 15×1 mm diameter is around 60 bar (for cold water), which in heating practice is never a limiting factor. Copper pipe is bacteriostatic – bacteria do not persist on its surface, which is important for sanitary pipework, but in closed heating systems this property is more of a bonus.

Disadvantages of copper: higher material cost (roughly 2 to 4 times more expensive than multilayer pipe of the same diameter), the need for skilled installation (soldering or pressing requires tools and experience), rigidity (harder to route through walls, cannot be wound into long coils), and electrochemical corrosion when combined with galvanized pipes or aluminium radiators without inhibitors. It is also worth mentioning that copper is sensitive to aggressive water with low pH – below pH 7.0, slow corrosion can occur.

Multilayer (composite) pipe

Multilayer pipe – also referred to in technical terminology as PE-AL-PE or PE-RT-AL-PE-RT depending on the polymers used – is today clearly the most widespread material for new builds and renovations of family houses in Slovakia. The principle is simple: the plastic inner layer (PE-RT or PE-X) ensures chemical resistance and a smooth surface, the aluminium foil in the middle provides a load-bearing/barrier function (prevents oxygen diffusion, reduces thermal expansion, holds shape after bending), and the outer plastic layer protects against mechanical damage.

For heating, two parameters are decisive: PN10 at T=70 °C and PN10 at T=95 °C. The first parameter describes continuous use at temperatures up to 70 °C (low-temperature underfloor heating, heat pumps), the second describes the ability to withstand higher temperatures with condensing boilers in combined systems. For example, multilayer pipe Ivar Turatec 16×2 mm or Ivar Turatec 18×2 mm are designed exactly for these conditions, making them a universal solution for most common installations.

Flexibility is a key advantage over copper: multilayer pipe can be bent by hand (with a bending tool or spring), wound into coils, and laid over long runs without joints. This significantly reduces the risk of leaks – every joint is a potential weak point. In underfloor heating, where the pipe lies in screed or concrete, the absence of joints under the floor is very important both technically and in terms of warranty.

Pure plastic pipe (polybutylene, PPR, PE-RT)

This category includes pipes made purely of plastic, without an aluminium layer. The best-known representative is polybutylene (PB) – a flexible plastic with good thermal resistance (up to 95 °C), which has been used in heating for decades, especially in Germany and Scandinavia. There are also PPR pipes (random copolymer polypropylene), which are welded using heat and are commonly used in boiler rooms and utility floors. And finally PE-RT (polyethylene with raised temperature resistance) – a pure version without aluminium, suitable for underfloor heating with lower temperatures.

Pure plastic has two main disadvantages compared to multilayer pipe: higher thermal expansion (up to 15× more than steel, meaning visible "pulsing" of pipes when heated) and oxygen permeability through the wall by diffusion. Oxygen in a closed heating system is insidious – it oxidizes pumps, valves, the boiler, and causes corrosion of steel components. That is why most boiler and component manufacturers require the use of a deaerator and inhibitors with pure plastic, or otherwise void the warranty.

Comparison of parameters: overview table

Where each material is really suitable: practical scenarios

Family house with a gas condensing boiler and underfloor heating

This is currently the most common case in Slovakia. Underfloor loops are almost always made of multilayer pipe – the most popular size is 16×2 mm for loops up to 80–100 m long, or 20×2 mm for larger rooms or higher heat losses. Multilayer pipe Ivar Turatec 20×2 mm in 100 m coils is suitable precisely for long loops or for horizontal distribution from the manifold to more distant circuits. Pipework from the boiler to the manifolds (the so-called primary circuit) can be copper or press-fit copper, or multilayer 26×3 or 32×3 mm depending on output. Important: a condensing boiler works with a return temperature of 30–45 °C and outlet temperatures of 50–70 °C, which is a comfortable range for multilayer PN10/95 °C pipe.

Boiler room with a cast-iron boiler and temperatures of 80/60 °C

Here, copper still holds firm. Short runs in the boiler room, direct connections of the boiler, circulation pumps, expansion vessel and safety valves – all of this is typically a copper installation joined by hard or soft soldering, or press fittings. Cast-iron boilers run at higher temperatures; at 80 °C multilayer pipe is still within a safe range, but in the immediate vicinity of the boiler, where temperature can briefly reach 90–100 °C, copper is the safer choice. Additionally, in older houses with existing copper pipework, it makes sense to stick with the same material to avoid problematic transitions between metal and plastic (which require special transition fittings).

Apartment renovation – radiator heating, pipework behind plasterboard

Multilayer pipe 16×2 or 18×2 mm is the clear choice here. It can be routed flexibly, direction can be changed without shaping fittings if needed, and press fittings or compression fittings are now standard for joints behind plasterboard, being reliable and inspectable. Compression fittings are the solution for places where you don't want to use a press tool – for example when connecting to a radiator, fitting or valve. Compression fitting for copper pipe 15×1 EK is used where the pipe is copper and you are connecting a threaded fitting or radiator valve to it. For multilayer pipe, combinations are available – EK adapter for PB pipes with 15 mm diameter allows connecting polybutylene or other 15 mm plastic pipe directly to an EK (eurocone) thread, which is the standard size for radiator valves on the Slovak market.

Heat pump – low-temperature system with underfloor and ceiling heating

Heat pumps operate with an output temperature of 35–55 °C, which is comfortable for any common plastic. Here the decisive factor is not temperature resistance but the oxygen barrier (the Al layer in multilayer pipe protects the heat pump's metal components from corrosion) and low hydraulic resistance (the smooth inner surface of plastic is more advantageous than the rougher surface of steel pipes). For horizontal distribution from the heat pump to individual circuits, sizes of 20×2 or 26×3 mm have proven effective, and 16×2 mm for underfloor heating loops.

Sizing: diameters, flow velocity and hydraulic losses

Choosing the correct diameter is just as important as choosing the material. Too small a diameter means high flow velocity, noise, erosion, and a high pressure difference that the pump must overcome. Too large a diameter means overspending on material and increased heat losses (a larger volume of water in the pipes means a slower system response). Practical recommendations for common family houses:

• Primary circuit boiler–manifold: 22×2 or 26×3 mm (multilayer), or 22×1 mm (copper) for output up to 15 kW
• Horizontal distribution to manifolds (secondary circuit): 18×2 or 20×2 mm
• Underfloor heating loops: 16×2 mm (standard size, maximum loop length 80–100 m at 70 mm spacing)
• Radiator connections (two-pipe system): 16×2 mm for series connection, 14×2 mm for star (home-run) connection (each radiator connected directly from the manifold)

A detailed calculation of the required number of metres of pipe, loop sizing and pipework planning can be found in the article How many metres of pipe do I need for a heating circuit: calculation and pipework planning, which is part of this Knowledge Centre. The explanation of the parameters PN10, T=70 °C and T=95 °C is discussed in more detail in the article Pipe temperature and pressure: what do PN10, T=70 °C and T=95 °C mean in practice?

Joining pipes: fittings, compression fittings and press connectors

Choosing the right connecting elements is just as critical as choosing the pipe itself. In practice, these are the main joining methods:

Compression fittings

A compression fitting works on the principle of mechanically clamping an olive onto the pipe using a tightening nut. It requires no special tools – just wrenches. The disadvantage is that the joint requires occasional retightening and is not suitable for concealed or embedded runs. For copper pipe, a compression fitting 15×1 EK is used – the olive clamps onto the soft copper and forms a tight joint. For polybutylene or plastic pipe, the procedure is slightly different – a correctly sized fitting with an insert must be used, for example the EK adapter for PB pipes with 15 mm diameter (Hepworth), where an internal insert prevents deformation of the soft plastic when tightening.

Press fittings

Press fittings are a professional method – the joint is formed by a pressing tool (hydraulic or electric) within seconds. The result is strong, permanent and suitable for concealed pipework. They are available for copper, multilayer and stainless steel pipes. Their disadvantage is the higher cost of fittings and the need to own or rent a pressing tool.

Soldering (copper)

Hard brazing (with or without argon, at 650–900 °C) and soft soldering (tin-silver, up to 400 °C) are classic methods for copper pipework. They require a gas torch, correct filler rods, flux and experience. An incorrectly soldered joint can last for years and then start leaking slowly – exactly when you least want it to. This is why soldering is really a job for professionals.

Welding (PPR)

PPR pipes are welded using an electric welding tool (socket fusion welding) – a temperature of approximately 260 °C melts the surface of both parts, which are then pushed together to form a monolithic joint. A very reliable method, but again requires a welding kit and practice.

Thermal expansion: why it matters in design

Thermal expansion of pipes is a parameter that tends to be underestimated when designing family houses, but it comes up repeatedly on jobs – as characteristic "cracking" noises from pipes behind the wall, or in worse cases, loosening of clamps and deformation of pipes when passing through expansion zones.

Example calculation: A 10 m length of multilayer pipe, when the temperature rises from 15 °C (installation) to 70 °C (operating), will elongate by: ΔL = 0.026 mm/m·K × 10 m × 55 K = 14.3 mm. That is more than a centimetre – with improperly secured pipe, this causes bending stress on fittings. The correct solution is to use expansion loops or U-bends on long straight runs and loose fixing (not fixed) where the pipe needs to expand. Copper pipe under the same conditions elongates only about 9.4 mm, which is significantly less.

Oxygen diffusion and corrosion in closed systems

This is a technical topic that is rarely discussed when selling pipe, yet it has a direct impact on the lifespan of the entire heating system. Oxygen enters a closed heating system in two ways: when topping up water and by diffusion through the wall of plastic pipe. Copper and multilayer pipe with an aluminium barrier are practically impermeable to diffusion. Pure plastic (PPR without a barrier, PE-RT without a barrier) allows small amounts of oxygen to pass directly through the pipe wall – nothing dramatic in a day, but over a year and across the entire pipe surface it is a measurable amount.

Oxygen in the system oxidizes steel boilers, cast-iron sections, circulation pumps and steel expansion vessels. The result is reddish sludge (magnetite and rust), which clogs valves, reduces the cross-section of pipes and shortens pump lifespan. That is why standard EN 1264 for underfloor heating directly requires the use of pipe with an oxygen barrier (class S5), or the use of a hydraulic separator (heat exchanger) between the circuit with plastic pipe and the primary boiler circuit.

Installation: what can be done yourself and what should be left to a professional

This is a question customers deal with very practically. The answer depends on the specific material and joining method:

• Multilayer pipe with compression fittings: a handy DIYer can manage this installation. The pipe must be cut correctly with a profile cutter (not saws!), the olive is slid on, checked, and tightened with a wrench. A detailed procedure is described in the article Installing multilayer pipe step by step: tools, fittings and compression fittings.
• Multilayer pipe with press fittings: technically straightforward, but requires a press tool (rental approx. €15–25/day). For runs that will be embedded or built into walls, we strongly recommend pressing over compression fittings.
• Soldered copper pipe: this is a job for a plumber. Flame, flux, solder, correct temperature and surface cleanliness – a mistake doesn't show up immediately, but a leak will start later.
• PPR welding: with the right kit and some practice, even a skilled amateur can manage it, but the first joints should be practised thoroughly. Too short a heating time = poor weld, too long = deformation. Every PPR thickness has a different time.

We recommend supplementing practical installation experience by reading the article How to correctly join copper pipe using a compression fitting without water leaks?, which describes the most common mistakes and how to avoid them.

Cost of the whole installation: material is only part of the story

Customers compare the price per metre of pipe, and copper comes out more expensive. But in a real job there are three cost components: material, fittings and labour. Copper pipe in a boiler room may require fewer fittings (bends are shaped directly), but every fitting and soldering joint takes time. Multilayer pipe is cheaper per metre, fittings are readily available, and with a star (home-run) layout from a central manifold, each circuit has a minimal number of joints.

In practice, for a family house (130–160 m²) with underfloor heating and a boiler room, the material cost of pipework (including fittings and connecting materials) with a copper boiler room + multilayer heating system typically comes to roughly €800–1,500 depending on scope and dimensions. A purely copper installation of the same scope would be 40–80% more expensive in materials, while the lifespan is comparable.

Frequently Asked Questions (FAQ)

Can I combine copper pipe with multilayer pipe in one system?

Yes, this combination is very common in practice – copper in the boiler room and multilayer pipe for distribution and underfloor loops. However, correct transition fittings must be used (copper thread → multilayer fitting), and care must be taken that the system is hydraulically closed with inhibitors, or that copper is not directly connected to zinc (galvanic corrosion). Copper and aluminium in a system are also a problematic combination – oxygen and electrolyte cause galvanic corrosion, so a closed system with inhibitors or deaerators is essential.

Is multilayer pipe safe at a temperature of 95 °C?

Yes, but only in the PN10 pressure class. Standard EN ISO 21003 precisely describes that PN10 pipe withstands continuous operation at 95 °C with a safety factor. In practice, a condensing boiler never maintains 95 °C for a long time, so the actual load is significantly lower than the maximum permitted. These parameters are explained in more detail in the article Pipe temperature and pressure: what do PN10, T=70 °C and T=95 °C mean in practice?

What is the actual lifespan of multilayer pipe?

Manufacturers state a lifespan of 50 years when operating conditions (temperature, pressure, correct installation) are met. Multilayer PE-AL-PE pipe has been on the market since the 1980s, and the first generations of installations are still functioning. The aluminium layer and polyethylene do not age chemically the same way as, for example, rubber sealing rings, which are actually the limiting element of lifespan in compression fittings (recommended inspection and possible replacement after 15–20 years for exposed joints).

Why must multilayer pipe not be cut with an ordinary hand saw?

An ordinary saw (hacksaw, jigsaw) does not create a perpendicular cut and mechanically deforms the end of the pipe – an oval cross-section prevents the olive or seal from seating correctly, and the joint will leak. The correct tool is a rotary profile cutter (pipe cutter) or a shear-type cutter for composite pipe, which ensures a precisely perpendicular, uncompressed cut. A detailed description can be found in the article Installing multilayer pipe step by step: tools, fittings and compression fittings.

Can I embed multilayer pipe directly in concrete in the floor?

Yes, multilayer pipe is specifically designed and intended for this – it is one of the main reasons for its popularity in underfloor heating. The condition is that there must be no joints (fittings or compression fittings) in the embedded run – the whole loop must be a single piece without interruption. Joints are only permitted in the accessible distribution box with the manifold. Multilayer pipe 16×2 mm is standardly supplied in 200 m coils, which is sufficient for most underfloor loops without any joints at all.

What should I do if I have a mix of old steel and new plastic pipes in the system?

This is a real situation with renovations. Steel pipes corrode from the inside and release sludge, which clogs new pumps and valves. The recommended solution is two-stage: before starting up the system, flush and chemically clean it (magnetic filter + cleaning flow), then install a magnetic filter on the return line to capture ferromagnetic sludge. A mixed system also needs regular topping up with corrosion inhibitors. More on regular inspection and maintenance in the article Maintenance and inspection of heating pipework: what to watch for every season?

Conclusion: which material to choose?

There is no single "best" material for heating – the right answer depends on the specific situation. Summarizing the requirements, the typical choice for 90% of Slovak family houses today looks like this: multilayer PE-AL-PE pipe for all underfloor heating pipework and secondary circuits, possibly with a copper connection in the boiler room where temperatures are close to the maximum and the space is open and accessible. PPR pipe makes sense for sanitary water and cooler secondary circuits, where there is no requirement for an oxygen barrier.

Basic sizes for a family house with underfloor heating are 16×2 mm for loops, 18×2 mm or 20×2 mm for horizontal distribution – depending on output and run length. For any doubts about diameter, number of metres, or the type of connecting material, we refer you to related articles in this Knowledge Centre, where you will find calculation procedures, concrete examples and step-by-step guides for common situations from practice.