Frequently asked questions about floor heating pipes

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Common questions about floor heating pipes – a comprehensive overview of practical answers

When a customer is about to implement a floor heating system, the number of questions that arise is surprisingly large. And that is even when it comes to an experienced craftsman or a careful investor who has thoroughly studied the entire installation. Floor heating pipes are not just a "pipe in concrete" – they are the heart of the entire system, from which the lifespan, efficiency, comfort, and ultimately the operating costs depend. In this article, I have gathered and processed the most frequently asked questions that repeat among customers, technicians, and DIY builders. You will find answers supported by real experiences from dozens of implementations, specific numbers, and practical recommendations.

1. What are floor heating pipes made of?

This is a basic question from which everything else depends. There are basically two main types of pipes used in floor heating systems on the market: PEX pipes (cross-linked polyethylene) and multilayer pipes (Pe-Al-Pe or Pe-Al-PEX). Each of these types has its own logic, advantages, and weaknesses.

PEX (cross-linked polyethylene) is produced by several technologies – PEX-a (Engel method, peroxide cross-linking), PEX-b (silane cross-linking), and PEX-c (radiation cross-linking). In terms of quality and properties, PEX-a is the best: it has the highest degree of cross-linking (typically over 70%), the best shape memory effect (after bending it returns to its original shape), and the best resistance to leakage under pressure at higher temperatures. This type is used, for example, in IVAR products, which you can find in our range.

Multilayer pipes have an aluminum layer that prevents oxygen diffusion into the water (which is important for metal components such as pumps and boilers) and keeps the pipe shape after bending – it does not spring back. This is an advantage when laying, but also a weakness when it comes to expansion, as it is less flexible in adapting to thermal length changes.

More on choosing between these types can be found in the article How to choose pipes for floor heating: PEX vs. multilayer and in the detailed comparison PEX pipes vs. multilayer pipes: differences, advantages and disadvantages.

2. What pipe diameter should I choose?

This is the number one question for customers who are buying pipes for the first time. In residential floor heating, several standard diameters are used: 16 mm, 17 mm, 18 mm, 20 mm, and 25 mm. Each has its own logic and it is not indifferent what you choose.

16 mm / 17 mm: The most commonly used sizes for standard living rooms. They allow for a longer circuit (up to about 80–100 m per one pipe) with a reasonable pressure drop. Pipe spacing is usually 10–20 cm.
20 mm: Suitable for longer circuits, larger rooms, or situations where dividing into multiple pipes is not practical. The volumetric flow is higher, which can be an advantage, but also a disadvantage (greater thermal inertia).
25 mm: Rather exceptional, used for large areas, industrial halls, or when a large flow with low pressure drop is needed. It is almost never used in a standard residential house.

In practice: if you plan standard living rooms (living room, bedroom, bathroom), go for 17 mm. It is the de facto standard today, balancing hydraulic resistance, flexibility, and price. Example from practice: for a 3-room apartment with a total heated area of 75 m² and a spacing of 15 cm, you will need about 500 m of pipe (including inlets and outlets). For such an order, the ideal is the PEX 17×2 – 600 m reel, which will cover the entire order without leftovers and joints.

Detailed calculations can be found in the articles What pipe diameter to choose for floor heating (16, 17, 18, 20, 25 mm) and How to calculate the length of pipe needed for floor heating.

3. What do the markings PN6 and PN10 mean and why does it matter?

This is a technical detail that many people overlook, yet it is important. PN means "Pressure Nominal" – nominal pressure. PN6 means the pipe is dimensioned for an operating pressure of 6 bar, PN10 for 10 bar. However, in practice, this is connected with temperature: the higher the water temperature, the lower the maximum allowable pressure.

Example for IVAR 17×2 PEX-a pipe:

At PN6, the maximum water temperature is +90 °C
At PN10, the maximum water temperature is +60 °C

For standard floor heating, the operating pressure of the system is typically 1.5–3 bar and the supply water temperature is 30–50 °C. This means that PN6 is more than sufficient in this case. PN10 is more relevant in combined systems where floor heating works together with radiators or heat exchangers, where the pressure can be higher.

In practice, therefore, there is no risk that you would need PN10 for standard floor heating. However, if you are buying pipe and you see that the manufacturer lists both values (for example, PN6/90 °C and PN10/60 °C), you don't need to be afraid – it is a standard designation, where you actually have two certified operating ranges in one product. A more detailed analysis can be found in the article Which pressure and temperature (PN6, PN10) suit my floor heating system.

4. How many meters of pipe do I need for one room?

This is a question everyone asks before placing an order. The answer depends on several factors:

Room area – the basic input
Loop spacing – standard is 10 cm (higher output, more pipe), 15 cm or 20 cm (lower output, less pipe)
Layout type – meandering or spiral snake
Length of supply and return lines from the manifold to the room

Approximate formula: pipe length (m) = area (m²) / spacing (m) + 2× supply length

Practical example: living room 25 m², spacing 15 cm (0.15 m), supply 4 m in one direction: 25 / 0.15 + 2×4 = 166 + 8 = approx. 174 m of pipe for this loop.

For smaller rooms (e.g., bathroom 6 m², spacing 10 cm, supply 3 m): 6 / 0.10 + 2×3 = 60 + 6 = 66 m.

When ordering pipe, it is practical to think in coils. For example, for a smaller order (one room or a bathroom), a PEX 17×2 coil – 120 m is sufficient. For a larger apartment or a family house with multiple loops, a PEX 17×2 coil – 240 m or even a wholesale coil of 600 m is more advantageous, where you save on the price per meter.

Important practical note: always keep a reserve of at least 10–15 %. The leftover pipe can be used for later repairs or test measurements. On the contrary, missing pipe is a problem – especially if you have already embedded the manifold into the wall and ordering "two meters" of extra will cost you more than the whole coil.

5. How is the pipe laid – meandering or spiral?

This is a question for which there is no single "correct" answer – it depends on the situation. Both methods are legitimate and commonly used.

Meandering (snake-like) layout is simpler to implement, less demanding in terms of bending, and is suitable for smaller rooms or situations where you want a warmer strip near the window (the supply branch runs along the cold perimeter wall). Disadvantage: one side of the room is always a few degrees warmer than the other, which can be noticeable in larger rooms.

Spiral (spiral) layout is more demanding to implement, requires more precise bending, but the result is a more even heat distribution across the entire surface. The supply and return are laid close to each other, so the heat is distributed more evenly. It is suitable for large living areas, where uneven temperature would be annoying.

In practice, most installers combine both approaches: spiral layout for living rooms and large areas, meandering for bathrooms, corridors, and smaller rooms. More about the practical procedure can be found in the article Installation of pipe for floor heating: spacing, laying and fixing.

6. What are the most common mistakes in the installation of floor heating pipe?

From practice, I know that there are several mistakes that keep repeating and most of them can be easily avoided:

Too long loops: A loop longer than 100–120 m (with 17 mm pipe) causes excessive pressure drop, uneven flow and problems with regulation. If you have a larger room, it is better to make two shorter loops than one long one.
Connections in the concrete screed: In principle, there should be no connections in the concrete – the pipe should run from manifold to manifold as one piece. No couplings, no crimped fittings under the screed. If it is otherwise, you are waiting for a problem.
Insufficient pressure testing: Before pouring concrete, the system must be filled with water, air must be purged and the system must be left under pressure for at least 24 hours. Most leaks appear exactly at that time. If the pressure does not drop, you can pour the concrete without worries.
Poor expansion joints: The concrete screed expands when heated. If expansion joints and expansion tape around the room are not properly made, cracks in the screed are only a matter of time. The pipe must pass through expansion joints in a protective sleeve.
Overheating during the first start-up: Concrete must "ripen" – usually 28 days before the first switch-on. Then the temperature is increased gradually, by 5 °C per day. A sudden jump to full power immediately causes cracking of the screed and damage to the pipe. More about this problem can be found in the article How to prevent overheating and damage to the pipe in floor heating.
Missing aluminum foil or thermal insulation under the pipe: If there is not enough thermal insulation under the pipe, the heat goes down instead of up. Result: a warm ceiling slab for the neighbor and a cold floor for you.

7. Why is the oxygen barrier important?

This is a tricky question that many installers do not realize the answer to until they encounter a problem. Pure PEX (without an oxygen barrier) is permeable to oxygen – not very, but permeable. Oxygen diffusing through the pipe wall into the system water causes corrosion of metal components: pumps, boilers, radiators, valves.

Multi-layer pipe with an aluminum layer has a natural oxygen barrier – aluminum is impermeable to oxygen. PEX-a pipe without a barrier is suitable only in systems where all components are made of plastic or stainless steel, or in systems where the primary loop is separated from the secondary loop by a heat exchanger (boiler, radiators).

If you have a standard condensing gas boiler, a cast iron pump or standard radiators and plan a direct connection with PEX pipe without an oxygen barrier – I recommend consulting the boiler manufacturer. Some boiler manufacturers condition the warranty on the use of pipe with an oxygen barrier (EVOH layer) or multi-layer pipe.

8. Can I use different pipe diameters in one system?

Yes, it is possible and sometimes even practical. For example: distribution pipes from the boiler to the manifold are made in a larger diameter (e.g. 20 mm or 25 mm), in order to reduce pressure drop over long sections. The floor heating loops in the rooms themselves then run in 17 mm. These diameters are connected on the manifold via appropriate reductions or directly, if the manifold allows it.

What is suitable for distribution pipes from the manifold for larger areas or longer routes is to use PEX pipe 20×2 – 200 m or PEX pipe 25×2,3 – 200 m for really long distribution routes or larger buildings.

What should not be done, however: changing the diameter within the floor heating loop itself (the snake). One loop = one diameter along its entire length. Any connection of different diameters inside the snake is also a potential leak point and a hydraulic fault.

9. How long will the pipe last in concrete?

This is a question to which manufacturers respond cautiously, but technicians from practice answer more directly. High-quality PEX-a pipe, when operating parameters are followed (temperature up to 60–70 °C, pressure up to 6 bar), has a declared service life of 50 years or more. In reality, the first PEX-a installations from the 80s and 90s are still in operation without problems.

However – and this is an important "but" – the pipe's lifespan depends directly on the quality of installation, the quality of the water in the system, and whether you have ever exceeded the operating parameters. Pipe that was exposed to a temperature of 95 °C for several hours due to a regulation failure may be internally damaged, even if it looks normal from the outside. Therefore, safety devices (pressure relief valve, temperature limiter) are a necessity, not just a formality. You will read more about these risks in the article Common faults and leaks in floor heating pipes: causes and solutions.

10. How is a leak detected in embedded pipe?

This is one of the most unpleasant situations a homeowner can encounter. Symptoms of a leak are: pressure drop in the system, wet spots on the floor or the neighbor's ceiling, dampness in the screed. Leak detection takes place in several steps:

Close all circuits on the manifold and monitor which circuit the pressure gauge indicates a drop. This identifies the circuit.
Pressurize the identified circuit with air or nitrogen and use an acoustic method (special probe) or a thermal camera to locate the leak.
In most cases, a small cut in the floor is required precisely at that location – thanks to localization, the intervention is minimal.

Prevention is always cheaper: perform pressure tests before pouring, do not use pipe from unknown sources, do not create joints in concrete. If you have doubts about the quality of the installation, a preventive inspection and pressure test every 5–7 years are reasonable measures. Learn more about maintenance in the article Maintenance and descaling of floor heating pipe: how to extend its lifespan.

11. Is it necessary to secure the pipe, or is it enough to lay it freely?

Securing is necessary for several reasons. First, the pipe has a tendency to return to its original coiled shape (especially PEX without an oxygen barrier). Second, during concrete pouring, the pipe can shift and change position, which also changes the spacing of the loops and the thermal performance. Third, unsecured pipe can rise (due to the buoyancy force of the concrete mix).

The following are used for securing:

Clips/clamps on profiles or mats – the pipe is pressed into a profiled strip or mat; spacing of clips about 50–80 cm on straight sections, 30 cm on curves
System profile boards – boards with protrusions, into which the pipe clicks; very fast installation, but higher price
Mesh (mounting grid) – the pipe is tied with plastic clips to a metal mesh; a proven and cheap method, but more labor-intensive

In practice, the method is chosen according to the budget and the scope of the project. For larger areas, the most economical option is mesh + clips, while for smaller spaces and when speed is emphasized, system boards are best.

Most frequently asked questions (FAQ)

Can I use pipe for floor heating also for potable water distribution?

Technically, PEX-a pipe can be certified for potable water (depending on the specific certification of the product), but pipe dimensioned and sold for floor heating may have various certifications and may not meet hygiene standards for potable water. Always check the specific certificate for the specific product. In case of doubt, use pipe explicitly certified for potable water.

What happens if we accidentally pour the pipe into concrete without a pressure test?

This is a common fear from the contractor's practice. If a leak appears only after pouring, you will either have to cut the floor (if you can locate the spot), or install a new loop on the surface in a profile. In the best case – if the leak is small and only in one place – the problem can sometimes be solved with epoxy injection, but this method has limited reliability. Conclusion: a pressure test before pouring is not a luxury, it is a necessary step.

What is the difference between PE-Xa, PE-Xb and PE-Xc?

All three are types of cross-linked polyethylene, but they differ in cross-linking technology. PE-Xa (Engel method) has the highest degree of cross-linking (≥ 70 %), the best shape memory effect, and the best properties at higher temperatures – it is a premium type. PE-Xb (silane method) and PE-Xc (radiation cross-linking) are cheaper to produce, but have a lower degree of cross-linking and worse properties under extreme conditions. In practice, all three are functional for floor heating, but for long-term reliability and quality, I recommend PE-Xa.

Can I bend PEX pipe manually, or do I need special tools?

PEX-a can be bent to a certain extent manually without a bender – it has good flexibility and returns to its shape, which is an advantage. The minimum bending radius for a 17 mm pipe is approx. 85–100 mm (5× outer diameter). For tight turns (e.g., in meanders), I recommend using a spring bender or a heat-forming tool. For multilayer pipe, a bender (e.g., pliers type) is a necessity – without it, the aluminum layer can slip and damage the sealing layer.

Is an expansion (dilation) strip required around the perimeter of each room?

Yes, without exception. A dilation strip (foam strip 8–10 mm thick) is glued around the entire perimeter of the room before pouring concrete. It compensates for the thermal expansion of the concrete screed – when heated, the concrete expands and without the strip, it would crack at the wall contact. For larger areas (over approx. 40 m²), internal dilation joints are also necessary – otherwise cracks will appear even in the perimeter dilation strip.

How long do I have to wait before starting heating after pouring the screed?

Cement-based screed needs at least 28 days to cure. Anhydrite screed is faster – usually 7–14 days. After this period, the temperature is increased gradually: first 3 days to 25 °C, then each day by 5 °C higher, until reaching the maximum operating temperature. This procedure (called "screed warming") prevents cracking. Skipping this process is one of the most common causes of damage to new floor heating systems.

Conclusion: what to take away

Tube for floor heating seems at first glance to be a simple thing – a hose in concrete. In reality, it is a system component, where every decision (material, diameter, loop length, laying method, pressure test) has long-term consequences. Installation errors are usually not easy to fix – and if they are, they are expensive. Therefore, it pays to invest time in the right selection and careful implementation.

If you are planning a small project (one room, bathroom), I recommend starting with a 17×2 – 120 m coil. For a larger apartment or family house, a 240 m coil or a wholesale package of 600 m is more economical. If you have doubts about dimensioning, choosing between PEX and multilayer pipe, or setting up the system, more detailed information can be found in other articles in our Knowledge Center.

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