2) Pipe

Multi-Layer Composite Pipe – in this type of pipe, inner and outer layers of polyethylene are tightly bonded to an inner aluminium pipe. This produces a pipe that is oxygen diffusion tight and easily bendable.

Technical Data

Our pipe is polyethylene/aluminium/polyethylene (PE-RT/AL/PE-RT) pipe, sometimes known as ‘multi-layer’ or ‘sandwich’ pipe.

PE = Polyethylene RT = Raised Temperature AL = Aluminium

Polyethylene is a thermoplastic, widely used throughout the world for consumer products. Its use is actively encouraged by groups such as Greenpeace and Friends of the Earth as a cleaner alternative to PVC based products.

  • Size - 16mm x 2mm outside diameter
  • Aluminium Core - 2mm
  • Operating Temperature - 70 deg C
  • Maximum Temp Peak Temperature - 95 Deg C
  • Maximum Working Pressure - 10 bar
  • Thermal Conductivity - 0.45 W/mK
  • Coefficient of Linear Expansion - 0.026 mm/m deg C
  • Water Volume @ 200mm centres = 0.85 litres per sm
  • Length of Pipe Runs for 16mm x 2mm pipe - 120 metres (max)
  • Pipe Spacing - 200mm standard (100mm/150mm around large windows etc., where heat will be lost. For sports halls - 300mm).

Oxygen Barrier

The aluminium core also serves as an oxygen barrier - if oxygen gets into the underfloor heating system, it will start to corrode the metal parts of the system, such as the boiler.

This sophisticated pipe has been developed specifically for the underfloor heating market and it has been carefully designed to offer optimum efficiency in terms of heat output per metre2 when evenly spaced in normal screeds, achieving even surface temperatures with the minimum amount of pipe. The aluminium core leads to quicker heating times and our pipe has the same heat output as a 20mm pex pipe.

The inner wall is smooth, so there is no starting point for the calcification of lime deposits in water, thus the pipe is non-corrodible.

The pipe is relatively soft and pliable requiring no special tools for laying. The pipe can be rolled out and secured in position with clips that are secured in the insulation or pressed into grooves in aluminium plates. When it is being laid, our pipe holds its shape and does not ‘snake’, which makes it faster and easier to install.

Extrapolation of long-term testing on our pipe shows that it will have a system life of between 50 years and 70 years and has a maximum pressure of 10 bar.

Pipe Spacing

In order to achieve an even heat output and to avoid ‘hot spots’ and ‘cold spots’ it is necessary for the pipe to be installed at even spacing and for the pipe not to be knocked out of position during screeding.

Our preferred insulation is EPS 100 Tackerboard (extruded polystyrene; 100 = commercial density). Tackerboard has a thick gridded cloth stuck to the surface of the insulation which has the dual purpose of protecting the insulation from the screed and ensuring that accurate pipe fitting is achieved by following the grid lines. The improved density of this insulation gives greater grip to the clips and helps to hold the pipe in position during screeding.


The inner and outer polyethylene pipes prevents scaling and corrosion and its unique combination of butt-welded aluminium and PE-RT ensures that our pipe is a full strength plastic alternative to copper. It has the advantages of both metal and plastic, but without the disadvantages of either.

There are a number of reasons why our pipe is the best available pipe for underfloor heating:

  1. Butt-welded aluminium pipe.
  2. 100% oxygen-tight and water vapour diffusion tight.
  3. Low coefficient of linear expansion.
  4. Entirely corrosion-resistant, also against chemicals and electro chemicals.
  5. Sound-insulation similar to entirely plastic pipe.
  6. Inner and outer pipe in durable PE-RT.
  7. High resistance to pressure and temperature.
  8. Smooth surface, less loss of pressure.
  9. Light as plastic piping.
  10. Flexible, easy to bend even at low temperature, retains curved shape.

The small bending radius, maximum flexibility and stability of our pipe make for a rapid, economical and reliable installation.

Pipe Loop Layout

The pipe loops can be laid out in several methods depending on the shape of the room and the position of external walls and windows where the highest heat loss occurs. In some rooms which have large areas of patio doors or roof lights it is sometimes appropriate to run the floor coils at closer spacing in order to increase the heat output to compensate for the higher heat loss in those areas.

The two most common pipe loop designs are the ‘snake’ and the ‘snail’.

Snake and the Snail

Whichever layout is used, the pipes cannot cross over in the floors and the flow and return have to run from and to the respective manifolds.
In order to ensure a satisfactory installation, it is essential to have a layout drawing prepared beforehand which sets out the routing and sequence of laying the pipework. Where a double pipe run is used this produces a contra-flow situation and this has the advantage of giving a more even distribution of heat over the whole floor area.

In order to keep the pump duty within reasonable limits there is a limit to the floor area which can be covered by one pipe loop and an approximate guide is that for 16mm tube the maximum pipe length would be 120 metres (22sm @ 200mm centres). Some larger rooms will therefore require two or more loops, while it may be possible to heat two smaller rooms with one coil. Ideally all the pipe coils should be approximately the same length in order to assist with balancing and regulating the system at the manifold.

Pressure Testing

Once laid, the pipe coils should be pressure tested at twice the working pressure – usually 3 bar - before the screed is laid. For our large projects we issue a Pressure Test Certificate for each manifold and all of our manifolds are supplied with a pressure gauge. Pressure gauges should be frequently monitored during screeding and the pressure should be maintained while the screed is being laid so that any damage to the pipework is highlighted by a drop in pressure. If the pressure gauge has dropped to zero, the pipe has been punctured. Screeding should stop immediately until the pipe has been repaired.

Pex Pipe

Cross linked Pex polythene pipe is available on the market; this pipe is perfectly adequate for underfloor systems, but it does not have an aluminium core, and is therefore less easy to work with as it needs more fixing to keep it in place. The oxygen barrier is often on the outside of the pipe, and as long as the pipe is treated with care there should be no problems with the installation. But if the pipe is dragged or roughly handled, there is a risk to the oxygen barrier being damaged. This is one of the reasons why, regardless of the type of pipe being used, installations should be carried out by experienced installers.

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UHMA - The trade association for surface heating and cooling.


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