Once people start looking into underfloor heating, they get the basic idea of how it works, and then they start to ask: should I choose PEX or copper?
The price of an installation is one of the things people care about right away. Copper is usually more expensive, both the material itself and getting someone to install it properly, since it takes more skill and time. PEX, on the other hand, is noticeably more affordable, which is a big reason you are seeing more residential and commercial projects switch over to it.
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Flexibility and Installation Speed
Then there is flexibility, and this is where PEX really fits. Underfloor heating means snaking pipe through long, winding routes under the floor, and PEX just bends and curves its way through that without a fuss. Copper is rigid, so you end up needing more joints and connections, which means more labour and more potential failure points. With PEX, installers can usually get the job done faster simply because there is less fitting work involved.
That point about joints deserves emphasis, because it carries a consequence beyond labour cost. Every joint buried in a screed floor is a connection you cannot inspect once the floor is finished. A continuous PEX loop running from the manifold and back with no joints in between removes that risk entirely, which is why underfloor heating installations are almost always designed with unbroken loops regardless of material.
Durability and Corrosion
On durability, both materials perform well over time if they are installed correctly and maintained. The main weakness of copper is that, under the wrong conditions, it can corrode. PEX does not have that problem since it is not a metal, so many people see it as the more worry-free option for modern systems. It also handles temperature changes well during normal operation.
There is an additional consideration specific to floors. Copper expands and contracts more noticeably with temperature change, and in a screed floor this movement can produce creaking or ticking sounds as the pipe works against the surrounding material. Certain screed chemistries can also be aggressive toward copper over time. Plastic pipe moves too, but its behaviour within screed is generally better understood and less troublesome in practice.
Thermal Conductivity: The Number That Matters Less Than It Looks
This is where a fair comparison needs to be honest. Copper conducts heat far better than any plastic. Copper sits around 400 W/m°K, while PEX is around 0.43 W/m°K at 60°C. On paper that looks like an overwhelming advantage.
In an underfloor heating system, however, it makes very little practical difference, and understanding why is useful. Heat leaving the water has to pass through the pipe wall, then through the screed, then through the floor covering before it reaches the room. The pipe wall is thin and represents only a small part of that total resistance. The screed and the floor covering dominate it. Improving conductivity at the pipe wall while the screed and tile remain unchanged is like widening one short section of a road when the traffic jam is further along.
What actually governs the heat output of a floor is pipe spacing, flow temperature, screed depth, and floor covering. Two systems, one in copper and one in PEX, designed to the same spacing and flow temperature, will deliver very similar output. This is why the material choice in modern underfloor heating comes down to cost, installation practicality, and system protection rather than conductivity.
Why the Oxygen Barrier Matters
One thing worth knowing about is the oxygen barrier. In a closed heating loop, oxygen can gradually diffuse through the pipe wall into the water and slowly attack metal parts elsewhere in the system, causing corrosion in pumps, boiler heat exchangers, and manifold valves, along with sludge that reduces flow. That is why modern plastic heating pipe includes an oxygen barrier layer, which protects the rest of the system.
This is a genuine difference between plastic and copper. Copper does not allow oxygen through its wall at all, so barrier performance is not a consideration with metal pipe. With plastic pipe it is essential, and it is a specification worth checking rather than assuming. The relevant standard is DIN 4726, which sets a limit on oxygen permeability. Pipe without barrier protection has no place in a closed heating circuit containing metal components, and using it is one of the more expensive mistakes available in this field, because the damage appears years later in components far from the pipe itself.
When Copper Is Still the Better Choice
Being straightforward about this matters. Copper has not disappeared, and there are situations where it remains the right specification.
Exposed pipework where appearance matters is one, since copper can be left visible in a way plastic generally cannot. Applications running above the temperature rating of plastic pipe are another. Copper is unaffected by ultraviolet light, whereas PEX degrades under prolonged UV exposure and must be protected during storage and installation. Copper also offers better fire performance, and it is not vulnerable to rodent damage, which is an occasional consideration in certain buildings and rural locations. Some specifications and local requirements simply call for metal pipe, and that settles the matter regardless of technical argument.
For the floor loops themselves, however, copper is now uncommon. It was used historically, and it works, but the combination of higher material cost, slower installation, rigidity in serpentine layouts, and joint count makes it hard to justify. Where copper still appears regularly in these systems is in the distribution pipework feeding the manifold rather than in the loops embedded in the floor.
Direct Comparison
| Factor | PEX | Copper |
|---|---|---|
| Material cost | Lower | Higher, and exposed to metal price movement |
| Installation | Fast, flexible, continuous loops | Slower, rigid, more joints required |
| Corrosion | Not affected | Possible under adverse water or screed conditions |
| Oxygen barrier | Required, check DIN 4726 compliance | Inherently impermeable |
| Thermal conductivity | Low, but rarely the limiting factor | Very high, with limited practical benefit in floors |
| UV exposure | Must be protected before installation | Unaffected |
| Typical use today | Standard for floor loops | Distribution pipework, exposed runs, special cases |
The Manufacturing Side
If you are curious about how these pipes are produced, Legom manufactures three floor heating pipe technologies at its facility in Jiaxing, Zhejiang Province, built to ISO and DIN standards, with oxygen permeability held to ≤0.32 mg/m²d at 40°C per DIN 4726 across the whole range.
The PEX pipe is cross-linked polyethylene at above 65 percent cross-linking per DIN 16892, which gives it high creep strength under sustained stress. It is chemical-free, resistant to microbial growth, and flexible enough to bend through tight loop patterns without becoming brittle. Because it is cross-linked, it is joined with expansion, crimp, or press fittings and cannot be heat-fused.
The PE-RT range works differently and this distinction matters when planning an installation. PE-RT achieves its temperature performance through a controlled crystalline structure rather than cross-linking, which means it can be joined using standard heat-fusion methods including socket, butt, and electrofusion. That makes field connections and mid-run repairs considerably simpler, since no dedicated expansion tooling is needed. The 5-layer version adds a central EVOH barrier layer between PE-RT layers and has a notably low thermal expansion coefficient, while the PE-RT Type II grade offers a Vicat softening temperature above 130°C for systems running at higher temperatures and pressures.
| Pipe Type | Joining Method | Vicat Softening | Best For |
|---|---|---|---|
| PEX | Expansion, crimp, or press fittings | 124°C | High creep strength in demanding pressure environments |
| PE-RT 5-Layer | Heat-fusion | 125°C | Lowest expansion plus a dedicated EVOH barrier |
| PE-RT Type II | Socket, butt, or electrofusion | Above 130°C | Higher temperature and pressure, easy field repair |
“The conductivity argument comes up constantly, and I think it deserves an honest answer rather than a defensive one. Copper does conduct heat far better than plastic, that is simply a fact. What people miss is that in a floor the pipe wall is a small part of the total thermal resistance, and the screed and floor covering above it dominate. Change the pipe material and the floor output barely moves. Change the pipe spacing and it moves a great deal. That is why the real decisions in these systems are spacing, flow temperature, and whether the pipe protects the metal components downstream. Anyone selecting pipe on conductivity alone is optimising the wrong variable.”
— Maggie Shen, Director of Legom
Making the Choice
At the end of the day, PEX and copper each bring something different in cost, flexibility, and ease of installation. Copper still has its place, particularly in exposed pipework and specialised applications, but more and more projects are leaning toward plastic for the floor loops themselves, simply because it is practical and holds up well over the long term.
Whichever material you choose, the pipe is only one part of the system. It connects to a manifold that distributes flow between the loops, with thermal actuators controlling each zone according to the room thermostat. Legom manufactures the complete range, so the components are designed to work together. For full specifications on the pipe range, see our floor heating pipe page or contact the technical team to discuss your project.
Frequently Asked Questions
Is the cost difference between PEX and copper significant on large projects?
Yes, and it compounds in two ways. The material itself is cheaper, and copper prices fluctuate with the metals market, which introduces budget uncertainty on projects with long lead times. The larger saving is usually labour: PEX installs faster because it bends through loop patterns without fittings, while copper requires cutting, joining, and supporting at every direction change. Across a large floor area with many loops, that difference in installation hours often exceeds the difference in material cost, which is why large residential and commercial schemes have moved decisively toward plastic.
How much does an oxygen barrier affect system lifespan?
Considerably, though the effect shows up in components other than the pipe. Oxygen diffusing through an unprotected plastic pipe wall enters the circulating water and oxidises metal parts elsewhere in the system, chiefly pumps, boiler heat exchangers, and manifold valves. The result is corrosion and sludge accumulation that reduces flow and can lead to premature component failure. The pipe itself remains unaffected, which is what makes the problem insidious: the damage appears years later in expensive components far from its cause. Barrier pipe meeting DIN 4726 prevents this, and it is the reason barrier specification is standard practice in closed heating circuits.
When is copper a better choice than PEX?
Copper suits exposed pipework where appearance matters, applications operating above the temperature rating of plastic pipe, and installations where fire performance or resistance to rodent damage is a specific concern. It is also unaffected by ultraviolet light, whereas PEX must be protected from prolonged UV exposure. Some specifications and local requirements mandate metal pipe, which settles the question directly. For floor loops embedded in screed, though, copper is now uncommon, and where it does appear in these systems it is usually in the distribution pipework feeding the manifold rather than in the floor itself.
Do climatic conditions affect how each material performs?
Not significantly during operation, since the pipe sits within a conditioned floor rather than exposed to outdoor weather. Where climate does matter is during installation. Plastic pipe can become stiffer and harder to handle in very cold conditions, so pipe with strong low-temperature impact resistance is worth specifying for winter installation in cold regions. Copper is unaffected by cold during handling but expands and contracts more with temperature change once in service, which in a screed floor can produce audible movement. Both materials perform reliably across normal operating conditions once installed correctly.
How do long-term maintenance costs compare?
Both are low-maintenance once installed properly, and neither requires routine servicing in the way mechanical components do. The meaningful difference lies in failure risk. Copper’s exposure is corrosion under adverse water or screed conditions, and joints buried in a floor are the most likely failure points, which is why minimising them matters. Plastic pipe does not corrode, and a continuous loop with no buried joints removes that risk almost entirely. The variable that most affects long-term cost is not the pipe at all but whether the circuit has proper oxygen barrier protection, since that determines the working life of the pumps and valves the system depends on.
Reviewed by Maggie Shen, Director at Legom, on July 28, 2026. This comparison of PEX and copper pipe for underfloor heating was reviewed for technical accuracy, including thermal conductivity in floor construction and oxygen barrier requirements under DIN 4726.