How It Works: Laying Low Profile Underfloor Heating

The exact kit components vary depending on the selected size and can be found either in the PDF assembly instructions or on the corresponding product page. You can also find additional accessories and suitable tools in our shop.

Please note

For all its simplicity, the following also applies to FLEXIRO thin-bed underfloor heating: Working on heating systems requires sufficient technical knowledge and skills. If in doubt, have the installation carried out by a specialist.

Determine the arrangement of the heating circuits. The installation location of the control box is selected so that the heating pipes of all heating circuits can be routed directly to the control box without extending the heating pipes.

Note: Set 2.5 m² = 1 heating circuit; 5.0 m² = 2 heating circuits; Set 7.5 m² = 3 heating circuits and 10.0 m² = 4 heating circuits

In principle, the underfloor heating pipes can be shortened. However, care must be taken to ensure that the differences in length between the individual connections are not too great (max. 15% difference in length).

The existing substrate must be level, clean, dry and stable. Any primer can be applied.

Before laying the pipework, determine the position of the underfloor heating manifolds. The arrangement of the heating system and the location of the RTL boxes can be planned individually. Ensure that the RTL valve is always accessible. It must still be possible to insert the pipe ends into the individual connections after the manifolds have been installed. The distance to the finished floor should be at least 20 cm from the lower edge of the concealed box.

For accurate and efficient temperature control, the RTL box should be positioned so that the thermostatic head can detect the temperature of the room air and the air can flow freely around it.

Please refer to the RTL box installation and operating instructions supplied separately.

The next step is to lay a sufficiently wide strip of edge insulation around the floor area to be heated. Columns or similar should also be surrounded by the edge insulation strip to allow the entire floor structure to expand.

The edge insulation strip is later filled with permanently elastic grouting.

The clip rails are installed according to the heating surface specified in the planning. The clip rails are fixed directly to the floor. Screws, dowels, impact dowels or construction adhesive can be used for this.

The fastening must be sufficient. It should no longer be possible to move the clip rails horizontally or vertically after installation. The rails should lie flat on the floor to ensure that the pipework is securely fixed.

When laying the underfloor heating, all distances specified in the installation drawing must be observed. The fixing distance of the clip rails is 40-50 cm, in the deflection area 10-25 cm.

Ideally, the heating pipe should be laid close to the manifolds to minimise the length of pipe required for the connection. The minimum distance between the pipes is 10 cm. The distance between the underfloor heating and the walls of the room should be at least 5 cm. A minimum bending radius of 8 cm must be maintained in the area of bends. The 10 mm PE-RT heating pipe is pressed into the clip rails. The pipes must be laid without twisting. The overhang of the pipe in the bend area should be approx. 10-25 cm. The loops can be fixed using dowel hooks.

If the heating pipe is damaged

Kinked or damaged areas of the heating pipe must be cut out. The pipe must be re-connected using a permanently sealed coupling. The coupling must be protected from direct contact with the casting compound by wrapping it in PE film. Mark the position of the coupling. After this repair the pipes may need to be extended.

A variety of installation designs are possible and can be adapted to suit the space available. A meandering or spiral installation is most commonly chosen.

The manifolds are connected to the RTL box with a Eurocone screw connection. The Eurocone has a self-sealing effect, while the metal screw connection has a purely locking function. Over-tightening must be avoided at all costs in order not to compromise the tightness of the heating system.

The heating pipes in the manifolds are connected using a simple plug-in system. The heating pipes, which are cut straight and shortened if necessary, are inserted directly into the plug-in connections of the manifold fingers as far as they will go.

As a rule, the FLEXIRO underfloor heating is integrated into the existing heating system in parallel with other radiators or as a replacement for an old radiator. This is done by inserting a T-piece (not supplied) into the flow and return pipes of the heating system.

Make sure that the flow and return are correctly assigned in the RTL box. Reversing the flow and return in the control box will disable the thermostatic valve and prevent the underfloor heating from operating.

Before commissioning the underfloor heating system it is essential to ensure that the system and all associated components are correctly installed and tight. The pressure test pump is available as an accessory in the shop.

See video for exact procedure and connections for pressure test

We strongly recommend carrying out a test run of the underfloor heating before covering the pipe system with levelling compound. This is the last opportunity to correct any installation errors or damage!

When selecting a suitable construction compound (levelling compound) for underfloor heating systems, attention should be paid to the "flexible" property. The underfloor heating must be switched off when applying the levelling compound! The minimum construction height is 12 mm if a ceramic surface covering is selected. For other top coverings, the levelling compound should have an additional covering of at least 5 mm of the heating pipe. All coverings must be labelled "suitable for underfloor heating".

Once the surface covering has been completed and allowed to dry naturally, the heating process can begin. If the floor is to be tiled, the underfloor heating should not be switched on until the tile adhesive is fully hardened. Heating is usually carried out according to a heating protocol. Follow the manufacturer's instructions for the construction chemicals used.