Pipe for underfloor heating is not one product. It is a loop pipe inside the floor, a distribution pipe between the plant room and the manifold, and occasionally a potable connection feeding the system. Each layer answers to a different standard. Treat them as interchangeable and you get coils that cannot be fused, a barrier that corrodes the boiler, or a submittal that fails review.
Key takeaways
- Floor loops run on PE-RT or PEX with an oxygen barrier; PP-R is for plant-room distribution and is not normally used as a flexible embedded floor loop.
- DIN 4726 caps oxygen permeation at 0.32 mg per square metre per day at 40 °C when the loop faces ferrous components.
- PE-RT pipe is specified to EN ISO 22391-2, PE-X to EN ISO 15875-2, multilayer to EN ISO 21003-2.
- A 16 mm loop is typically capped around 80–100 m; 20 mm runs 100–120 m, depending on pressure drop.
- At 150 mm spacing you need about 6.7 m of pipe per square metre; at 200 mm spacing about 5 m.
- Credential scope matters more than a logo: ask which SKUs a certificate covers and verify listings in the public directory.
- Hitze runs SKZ-tested PE-Xb heating pipe with no MOQ on general ordering and private-label printing, and takes a sample-first approach for new buyers.
This guide is written for importers, distributors and wholesalers who stock or specify radiant heating lines, not for one-off DIY buyers. It covers the four material families, the governing standards, the barrier decision, the coil math for ordering, and the factory checks that keep a container out of trouble.
Why Underfloor Heating Pipe Is a Specification Decision
A floor hides its pipes. Once screed is poured, a loop failure means breaking a finished surface. The material choice is made once and paid for every year the building stands. That is why the specification matters more here than in an accessible plant room, where a bad joint costs an afternoon to replace.
The failure modes are specific to this application. Oxygen bleeds through the pipe wall and corrodes ferrous pumps and boilers. Wrong loop length starves the far end of the room of heat. A barrier pipe mistakenly run on a potable circuit can fail its water-contact approval. None of these show up on day one.
The buying decision splits into three layers. The loop pipe must bend, hold pressure at heating temperatures and resist oxygen diffusion. The distribution pipe from the boiler room to the manifold must handle higher flow and temperature. The potable connection, where present, must satisfy drinking-water rules. DIN 4726 oxygen-barrier requirements explain why the loop layer needs a material the plant room may not.
Plan the whole system before ordering coils. A distributor who stocks only 16 mm barrier PE-RT cannot serve a project with PP-R distribution. A specifier who allows any loop material without a barrier clause invites a corrosion claim later. The layers below walk through each decision in order.
The Pipe Materials That Run Under a Floor
Four material families dominate hydronic floor heating. Each is a different polymer with a different jointing method, so the choice is not a brand preference; it is an installation-system decision.
PE-RT
Polyethylene of raised temperature resistance is the workhorse of modern floor loops. PE-RT is thermoplastic and can be heat-fused in approved systems. However, embedded underfloor-heating loops are normally installed as continuous, joint-free coils, with connections kept at the manifold. It is forgiving during installation. Its pipe standard is EN ISO 22391. PE-RT is common in 16 mm and 20 mm coils with a co-extruded EVOH barrier.
PE-X
Crosslinked polyethylene cannot re-melt once crosslinked, so it cannot be heat-fused. Joints use mechanical connections such as compression, press and push-fit. The manufacturing letter matters: PEX-a, PEX-b and PEX-c differ in how the crosslinking is done, and regional markets favour different letters. The pipe standard is EN ISO 15875.
PEX-AL-PEX and multilayer
A butt-welded aluminium core between two PE-X layers adds form stability and holds a bent shape without extra fittings. The barrier itself does not drive thermal expansion; the pipe material does. Typical published coefficients run about 0.2 mm per metre per kelvin for PE-X and PE-RT, and about 0.025-0.03 mm per metre per kelvin for aluminium-composite pipe. The aluminium layer also blocks oxygen diffusion completely, so no separate EVOH coating is needed. Multilayer systems are specified to EN ISO 21003.
Polybutene and others
Polybutene pipe appears in some European markets, and a few systems still run on non-barrier PEX for open-loop or boiler-room use. Treat these as regional variants, not defaults for a closed hydronic floor.
| Material | Standard | Jointing | Typical role |
|---|---|---|---|
| PE-RT | EN ISO 22391-2 | Socket fusion or mechanical | Floor loops |
| PE-X | EN ISO 15875-2 | Mechanical only | Floor loops |
| PEX-AL-PEX | EN ISO 21003-2 | Mechanical or press | Loops needing shape stability |
| PP-R | EN ISO 15874 | Socket heat fusion | Plant-room distribution |
The loop-size question usually settles on 16×2.0 mm as the common stock unit, with 20 mm for larger rooms. The deeper decision is jointing culture: a market used to fusion will buy PE-RT, while a market built on press tools will standardise on PE-X or multilayer. PE-RT vs PEX for underfloor heating compares the two loop families in detail, and multilayer pipe sizing guidance covers the flow side of the choice.
Standards That Govern Underfloor Heating Pipe
Each material has a pipe standard, and the system has its own standard on top. Reading the correct line on a datasheet keeps a submittal out of review limbo.
- EN ISO 22391-2 — PE-RT pipes for hot and cold water installations. This is the standard a PE-RT floor-loop datasheet should cite.
- EN ISO 15875-2 — crosslinked polyethylene pipes. PEX loops cite this family, with the production method noted as PEX-a, PEX-b or PEX-c.
- EN ISO 21003-2 — multilayer piping systems inside buildings. PEX-AL-PEX and other composite constructions cite this.
- ISO 10508 — the classification and design-guidance standard. It assigns service classes; Class 4 is the design class for underfloor heating and low-temperature radiators.
- EN 1264 — the system standard for water-based surface heating and cooling, covering design, installation and commissioning. EN 1264-4:2021 is the installation part.
- DIN 4726 — the German requirement for plastic pipe in warm-water surface heating systems, dominated by its oxygen-permeation limit.
A pipe can meet its own material standard and still fail the system requirements. The loop pipe needs a barrier when the circuit contains ferrous parts, and the installed system has to be commissioned per EN 1264. The BS EN 1264 series is the reference for the system layer, and EN 1264-4:2021 covers installation specifically.
The standards also drive the import file. A datasheet that names no standard is a red flag; one that names the wrong standard for the material is worse. The PE-RT pipe standard EN ISO 22391-2, the PE-X standard EN ISO 15875-2 and the multilayer standard EN ISO 21003-2 are the certificate titles a buyer should expect. For service-class logic, BS ISO 10508 is the classification reference.
The Oxygen Barrier and When It Is Mandatory
Oxygen enters heating pipe by diffusion across the wall, driven by a concentration gradient rather than by system pressure. Hotter water accelerates the process, and the corrosion it causes is self-sustaining because consumed oxygen keeps the gradient alive. In a closed loop, the ferrous victims are cast-iron pumps, steel boilers and heat exchangers, which shed magnetite sludge as they corrode.
The German requirement is DIN 4726, published by DIN Media and sold through the official store. The current edition is DIN 4726:2024-12, which replaced the 2017-10 text. It limits oxygen permeation to 0.32 mg per square metre per day at 40 °C. Values at higher temperature are not published in the open standard, so confirm them against the current edition before quoting them on a datasheet. The DIN 4726:2024-12 standard page is the citation a specifier should accept. The older industry shorthand of roughly 0.1 mg per litre of water per day means the same thing in different units.
Two constructions pass the barrier test. EVOH, a co-extruded copolymer layer, is the usual answer on flexible PE-RT and PEX loops, typically in a five-layer build. Aluminium-core PEX-AL-PEX needs no EVOH because solid aluminium blocks diffusion outright, which is why the factory cutting a clean end looks for a bright aluminium ring.
Barrier is not universal. Open hydronic systems, where oxygen is replenished anyway, gain little from it, and whether an oxygen-barrier pipe is suitable for drinking water depends on the specific SKU’s drinking-water certification. Keep barrier and non-barrier stock separated in the catalogue. Make the potable boundary explicit, because the wrong coil in the wrong circuit is a warranty argument waiting to happen.
Sizing Loops and Coils Without Guessing
Ordering the right quantity starts with two figures: pipe per square metre and loop length. The per-square-metre number is pure arithmetic. At 150 mm spacing, one metre of pipe covers 0.15 metres of width, so you need about 6.7 m per square metre. At 200 mm spacing the figure drops to about 5 m per square metre. Add waste for cuts, connections and edge zones.
Loop length is a hydraulic limit, not a comfort choice. Typical design caps run about 80–100 m for 16 mm pipe and up to 120 m for 20 mm, depending on pressure drop and flow rate. These are trade practice figures, so confirm the design calculation for each project rather than treating them as fixed values.
Coils come in standard lengths that suit different projects. Common stock units are 200 m, 300 m, 500 m and 600 m coils, again as typical trade practice rather than a standard requirement. A distributor planning a container needs the coil mix that matches local room sizes. A 600 m coil does a poor job of serving a 40 m² flat.
| Spacing | Pipe per m² | Typical loop size | Typical loop cap |
|---|---|---|---|
| 150 mm | ≈ 6.7 m | 16×2.0 mm | 80–100 m |
| 200 mm | ≈ 5 m | 20×2.0 mm | 100–120 m |
Typical flow temperatures for floor heating run 35–45 °C, which is lower than radiator systems and friendly to heat pumps. Floor surface temperature is capped for comfort, with design figures around 29 °C in occupied zones and 35 °C in edge zones. Those are common design estimates, so check the current EN 1264-2 text for the project requirement. The underfloor heating manifold installation guide covers the connection and commissioning side of the same system.
What PPR and PPR-CU Do in a Radiant System
The short answer to a common question: PP-R is not normally used as a flexible embedded floor loop. It is rigid, and a loop needs to bend to the spiral or serpentine layout. PP-R’s job is distribution, from the plant room to the manifold. Socket heat fusion creates homogeneous joints, and the pipe carries higher flow and temperature than a loop would.
PP-R is governed by EN ISO 15874 and DIN 8077/8078, and Hitze publishes a dedicated service-class explainer on EN ISO 15874. The plant-room layer is a genuine cross-pillar sale: a distributor stocking flexible loop pipe can carry the PP-R distribution range as the matching upper layer of the same system.
PPR-CU, the copper-lined variant, suits hygiene-sensitive potable connections feeding a heating system where drinking water is in play. Hitze’s PPR-CU range runs OD 20–63 mm. Potable claims need current test evidence per model. Treat the copper lining as a construction feature and verify water-contact approval for the exact SKU before you promise it.
For wholesalers building a full radiant line, this is where the PPR world and the flexible-loop world meet. Hitze’s importer and distributor piping program consolidates both families on one order. That avoids two suppliers, two freight bills and two document packs for one system.
How to Vet an Underfloor Heating Pipe Supplier
Every factory prints a certificate list. The difference between a good coil and a liability shows up in the scope of those credentials and in what the factory actually checks on the line. Below is the vetting sequence Hitze runs on its own underfloor heating pipe range and recommends a buyer apply to any supplier.
Credential scope beats credential names. Ask which SKUs a certificate covers, when it was issued, and how the buyer verifies it in the issuing body’s public directory.
- Certificate scope: Hitze holds SKZ testing on PP-R pressure pipe, PP-R fittings and PE-Xb heating pipe, plus a SAI Global StandardsMark to AS 4176.8 for multilayer. The company also states WRAS product approval on the PP-R and PEX lines; the certificate reference is provided on request and should be checked against the public WRAS approvals directory.
- QC sequence: Resin is verified before extrusion. OD, wall thickness at multiple points and ovality are checked against the S-series tables. Pipes, fittings and fused joint assemblies are pressure-tested on in-house hydrostatic benches against DIN and EN ISO thresholds.
- Samples and ordering: Hitze general ordering has no minimum order quantity, is sample-friendly, and supports private-label and ODM printing.
- Warranty: As stated in our company profile, Hitze offers a 50-year product warranty, confirmed as a commercial posture. Confirm inclusions and exclusions for your project, and keep it separate from a standard’s 50-year design-life calculation.
- Company scale: As stated in our company profile, GERMANY Hitze INDUSTRY CO., LTD. was founded in 1974, runs a 120,000 m² production base with 1,000+ employees and exports to 118+ countries.
What changes the quote matters as much as the pipe itself. Resin grade, barrier construction, coil length, print and packaging all move the price, so two quotes on bare 16 mm PE-RT are not comparable. Send the same spec line to every factory and compare the replies line by line.
Pipe Selection Checklist for Importers and Distributors
The checklist below turns this article into a purchase order. Copy it into an RFQ email so every factory quotes the same line.
- Material and standard: PE-RT to EN ISO 22391-2 or PE-X to EN ISO 15875-2, stated with the production letter for PEX.
- Barrier construction: EVOH co-extruded or aluminium-core, with the DIN 4726 permeation limit stated on the datasheet.
- Size and coil units: OD and wall thickness, coil lengths, and the loop-size mix for your market.
- Document pack: datasheet, test reports, certificate scope by SKU, and Declaration of Performance where applicable.
- Sample step: a coil sample cut, fused and pressure-tested before the container order.
- Distribution layer: PP-R for plant-room runs, with PPR-CU specified only where potable contact is proven for the SKU.
A matched system beats a mixed one on warranty and on commissioning. When the loop pipe, the distribution pipe and the manifolds come from one factory, there is no third party to blame when a joint weeps under test. The manifold side of the decision is covered in the brass vs stainless manifold guide.
Conclusion
The floor hides every mistake, so the pipe decision is the one that has to be right the first time. Choose the loop material by installer practice and barrier need. Govern it with the correct standard, and buy from a factory that proves credential scope rather than printing a list.
Start with the sample. Send Hitze your target sizes and coil lengths, verify the certificate scope for the exact SKUs, and build the distribution layer in the same order. The Hitze team can walk a wholesaler from one coil to a container mix without changing suppliers mid-system.
Frequently Asked Questions
Can PPR pipe be used for underfloor heating?
PPR suits plant-room supply and return distribution and is not normally used as a flexible embedded floor loop. Flexible PE-RT or PEX pipe carries the loops because it bends to the layout and absorbs expansion.
Is PE-RT or PEX better for underfloor heating?
Both are proven loop materials. PE-RT is thermoplastic and can be heat-fused in approved systems. However, embedded loops are normally installed as continuous, joint-free coils, with connections kept at the manifold. PE-X uses mechanical connections and holds shape memory. Pick by installer practice and system design.
What does DIN 4726 require for heating pipe?
DIN 4726 caps oxygen permeation through the pipe wall at 0.32 mg per square metre per day at 40 °C. That protects ferrous pumps, boilers and heat exchangers in closed loops.
How much underfloor heating pipe do I need per square metre?
About 6.7 m per square metre at 150 mm spacing and 5 m per square metre at 200 mm spacing, before an allowance for waste and edge zones.
How long can an underfloor heating loop be?
Typical design caps run about 80–100 m for 16 mm pipe and up to 120 m for 20 mm pipe, depending on pressure drop and flow. Confirm the hydraulic calculation per project.
Do I need oxygen barrier pipe on every radiant job?
Barrier is needed in closed hydronic loops with ferrous components. Open systems gain little from it, and whether an oxygen-barrier pipe is suitable for drinking water depends on the specific SKU’s drinking-water certification.
