UFH pipe pressure and temperature ratings explained (PERT, PEX, MLCP)

Every UFH pipe has a pressure and temperature printed on it or in its data sheet, such as "6 bar at 70°C". Those two numbers belong together. Plastic pipe gets weaker as it gets hotter, so a pressure rating only means something when you know the temperature it was given at, and for how long.

This guide explains how pipe ratings work, what the application classes mean, how PERT, PEX and multilayer pipe compare, what pressures and temperatures a real UFH system runs at, and what to test it to. For the wider differences between pipe types, see UFH pipe types compared.

What does "6 bar at 70°C" mean on UFH pipe?

It means the pipe is designed to carry water at up to 6 bar while the water is at up to 70°C, over its design life. It does not mean the pipe will burst at 7 bar, or that it can run at 70°C all day for 50 years. Plastic pipe ratings come from a temperature profile: a mix of temperatures for set periods, each with a safety factor added.

The Class 4 profile shows how this works. Kiwa's certification scheme for PE-RT underfloor heating pipe sets out a 50-year profile:

Condition	Temperature	Time over 50 years
Cold	20°C	2.5 years
Design	40°C, then 60°C	20 years, then 25 years
Maximum	70°C	2.5 years
Malfunction	100°C	100 hours

Pipe made to this profile is used at a design pressure of 4 or 6 bar. Kiwa notes that for floor heating in tall buildings, where the static pressure is higher, the design pressure should be 10 bar.

What are the pipe application classes?

Application classes are standard temperature profiles from ISO 10508. A pipe is rated for a class at a stated pressure, so you can compare pipes from different makers on the same basis. The two that matter for home heating are Class 4 and Class 5.

Class	Use	Design temperatures	Maximum	Malfunction
Class 4	Underfloor heating, low-temperature radiators	20°C, 40°C, 60°C	70°C	100°C for 100 hours
Class 5	High-temperature radiators	20°C, 60°C, 80°C	90°C	100°C for 100 hours

The Class 5 figures are from Kiwa's scheme for heating pipe used on radiator connections, at a 6 bar design pressure. The practical point is simple: Class 4 pipe is for the floor. If you want to run a radiator circuit at 80°C, use pipe rated for Class 5 or a higher-rated multilayer pipe.

How do PERT, PEX and multilayer pipe ratings compare?

For underfloor heating, all three are suitable at the temperatures a floor runs at. The differences show up at the top of the range and in the pressure rating.

Pipe	Example rating	Source
3-layer PERT-EVOH, 16 x 2.0mm	6 bar at 70°C, short-term peak 95°C	MaxHeatUFH product data
5-layer PERT-EVOH, 16 x 2.0mm	6 bar at 70°C, 10 bar at 20°C, peak 95°C	MaxHeatUFH product data
PE-Xa with EVOH (UFH pipe)	Class 4, 6 bar at 70°C, malfunction 100°C	Manufacturer data
PE-Xa with EVOH (radiator pipe)	Class 5, up to 90°C continuous	Manufacturer data
Multilayer PE-RT/aluminium, 16 x 2mm	10 bar, 70°C working, 95°C max flow	Manufacturer data

Our 3-layer PERT-EVOH pipe and 5-layer PERT-EVOH pipe share the same pressure and temperature rating. The 5-layer version has the oxygen barrier sealed inside the wall, which protects it from scuffs on site. Both are tested oxygen tight to DIN 4726. Our guide to oxygen barrier pipe explains why that matters.

Multilayer pipe, such as our PERT-AL-PERT pipe, has an aluminium layer that carries much of the pressure. That is why multilayer pipes commonly carry higher pressure ratings than plastic-only pipe of the same size. Always check the rating of the exact pipe and fittings you use, because the system is only as good as its weakest part.

Why does a pipe's pressure rating drop as the temperature rises?

Because plastic slowly softens and creeps under load, and it does so faster when it is hot. A pipe that holds 10 bar at 20°C may only be rated for 6 bar at 70°C, as our 5-layer PERT-EVOH data shows. The standards build this in by testing pipe at high temperatures for long periods and then applying service coefficients, which are safety factors of 1.0 to 1.5 in the Class 4 profile.

So the short-term peak figure, such as 95°C, is not a working temperature. It is there so that a fault, such as a failed mixing valve sending boiler water into the floor, does not ruin the pipe straight away. It is not a reason to run the floor hot.

What temperature and pressure does a UFH system actually run at?

Far below the pipe's limits. BEAMA's UFH controls guide gives a typical design flow temperature of 40 to 55°C for systems fed by a boiler through a blending valve. One leading manufacturer's screed guide designs its circuits at a 50°C flow temperature, and says floor surface temperatures must not exceed 27°C with timber floors.

The floor is protected from boiler water by two devices:

• A blending or mixing valve, which BEAMA says must be fitted when a standard high-temperature boiler is the heat source. Our pump and blending valve packs hold a set flow temperature between 20 and 55°C.
• A high limit thermostat, which BEAMA says prevents water above 60°C entering the UFH loops if other temperature controls fail.

Those two limits, 55°C in normal use and 60°C as a safety cut-out, keep the pipe well inside its 70°C maximum. A heat pump runs cooler still. Our guide to UFH flow temperatures goes into the settings.

On pressure, the pipe rating matters most during pressure testing, which deliberately takes the system higher than it will normally run.

What pressure should I test UFH pipe to?

Test at 6 bar for at least an hour before any screed or floor covering goes down. That is one leading manufacturer's figure in both its floating floor guide and its plumbing pressure testing guide. The same manufacturer's plumbing guide adds that the pressure can then be lowered to 3 bar while floor coverings are laid.

For screeded floors, one leading manufacturer says to keep the system pressurised at 6 bar while the screed goes on, to protect the pipe walls. A few other points from the same guides:

• Use water, not air. One leading manufacturer says its products must not be air tested, for health and safety reasons.
• Watch for frost. In sub-zero conditions, drain the system after testing and screeding.
• Test the whole circuit. Include the manifold and connections, not just the pipe in the floor.

A hydraulic test pump makes it easy to reach and hold the test pressure. Our step-by-step guide to pressure testing underfloor heating covers the full procedure.

Frequently asked questions

What is the maximum pressure for UFH pipe?

It depends on the pipe and the temperature. Our PERT-EVOH pipe is rated 6 bar at 70°C and the 5-layer version 10 bar at 20°C. Multilayer pipe is often rated 10 bar. Always read the pressure together with its temperature.

What is the maximum temperature for underfloor heating pipe?

Class 4 UFH pipe is rated to a maximum of 70°C, with 100°C allowed only as a short malfunction of up to 100 hours over its life. Our PERT-EVOH pipe allows a short-term peak of 95°C.

Can I connect UFH pipe straight to a boiler?

Not without a blending valve if the boiler runs hotter than the floor needs. BEAMA says a blending device must be fitted with a standard high-temperature boiler, and a high limit thermostat should stop water above 60°C reaching the loops.

Is PEX better than PERT for underfloor heating?

Both are made for Class 4 underfloor heating, and at normal floor temperatures of 40 to 55°C both work well. PEX is often used where higher temperatures are needed, such as Class 5 radiator pipe.

Can I use UFH pipe for radiators?

Only if it is rated for the radiator temperatures. Class 4 pipe is for floors and low-temperature radiators. For radiators at 80°C, use Class 5 pipe or a suitably rated multilayer pipe.

What pressure should I pressure test UFH to?

6 bar for at least one hour before screed or floor coverings go down. One leading manufacturer says the pressure can then be lowered to 3 bar while coverings are laid. Use water, never air.

What does Class 4 mean on a pipe?

It is the ISO 10508 temperature profile for underfloor heating and low-temperature radiators: 20 to 60°C in normal use, 70°C maximum and 100°C as a short malfunction.

Sources: Kiwa BRL 5602: PE-RT pipe for underfloor heating (Class 4 profile), Kiwa BRL 5605: radiator connection pipe (Class 5 profile), BEAMA underfloor heating controls guide, and manufacturers' installation guidance to BS EN 1264