Frequently Asked Questions with Answers about our Radiant Heating Kits

Underfloor Heating Kits and RTL Temperature Control


Is it also possible to modernise large rooms greater than 10m² in size with a FLEXIRO low profile underfloor heating kit?

You can install several FLEXIRO kits in one large room. You will then need to install several Kompa boxes as well.

My bathroom is 8.5m² in size. Which FLEXIRO kit should I use?

In the bathroom, there are many surfaces on the floor that can remain inactive because they do not transfer heat efficiently to the room anyway. This is the case, for example, under the bathtub. If you do not thermally activate this area, then a 7.5m² kit is already sufficient.

What is the difference between Multibox 4K-RTL und der Kompabox RTL?

The Kompabox RTL is used exclusively in conjunction with conventional heating systems with high flow temperature. The Multibox can also handle radiant heating systems with lower flow temperatures. Check our head-to-head comparison of temperature control boxes.

What are the exact installation dimensions of the offered temperature control boxes??
  • Installation dimensions Multibox 4K-RTL in mm: 190×240×60 (H×W×D), threaded connection 3/4"
  • Installation dimensions Kompabox RTL in mm: 150×230×60 (H×W×D), threaded connection 3/4"
Do you also make individual offers for radiant heating systems?

We at FLEXIRO have put together kits for you that are specially designed for modernising smaller areas. This makes it easy to plan your new radiant heating. However, please feel free to get in touch with us if your project requires an individual solution: Contact form.

Installation and Technology


The completely installed FLEXIRO radiant heating does not get warm?

The components of the FLEXIRO sets are carefully dimensioned to match each other in terms of technology. It is very unlikely that the heating pipes will not allow sufficient heating water to pass through if they are installed correctly. If the heating surface does not get warm, please first check whether the Multibox or Kompabox is correctly connected to the flow and return of the heating system. Perhaps only one heating pipe has been kinked. If several heating circuits were installed, one heating pipe may have been disproportionately shortened in length. As a result, the heating circuit with the longest connection pipe may not heat up properly. The pipe lengths of the individual heating circuits should be approximately the same.

What is the heating capacity of the kits?

The heating capacity in general depends on the installation distance, insulation and floor covering, etc. The information in our product flyers provides data on the average heating capacities of the kits.

Can underfloor heating be installed without additional insulation?

Due to the installation of the low profile underfloor heating directly below the surface, additional insulation is not required in most cases. This keeps the installation height low. Exceptions are floors above unheated basements and the ground. The requirements of the Energy Saving Ordinance must be observed. Further information on thermal insulation for underfloor heating

What are the advantages of FLEXIRO low profile underfloor heating kit compared with other systems?

Particularly when modernising existing buildings, there is often insufficient room height to install underfloor heating. Conventional underfloor heating has a construction height of 100 mm and more. The old floor would have to be completely ripped out and disposed of. This results in additional costs and considerable work. Milling grooves into existing concrete floors is also labour-intensive and requires special milling machines. Moreover, this is only possible if the floor slab’s structural capacity allows grooves to be milled. This effort is generally not justifiable, especially for small heating surfaces.

With a construction height of just 17mm (without the surface covering), the FLEXIRO low profile underfloor heating kit therefore provides an excellent option when modernising small heating surfaces and, in particular, individual rooms.

What is the construction height of the various FLEXIRO underfloor heating kits?

The height of the knobbed mat and clip rail with the heating pipe is 14 mm. In addition there is the self-levelling compound, which must be laid according to the manufacturer's specifications. The self-levelling compound should have a depth of at least 3 mm for ceramic surface coverings (tiles etc.). This results in an average construction height of 17 mm without the surface covering.

Which surface covering is suitable for FLEXIRO underfloor heating?

The surface covering has a big influence on the energy efficiency and the response time of the FLEXIRO underfloor heating. If possible, select a covering that has good thermal conductivity. Ceramic tiles are particularly suitable. Materials such as cork or timber floorboards and parquet take a long time to warm through and require a higher supply temperature.

What kind of substrate must be used to install the FLEXIRO system?

The existing substrate must be level, clean, dry and load-bearing.

Can FLEXIRO underfloor heating also be installed on floorboards?

The Bostik company says yes! However, floating timber structures are not permitted as they are highly susceptible to deformation. Installation is therefore only possible on fixed timber structures, whereby these must be uncoupled. Please contact us for further information on laying on fixed timber structures!

Can FLEXIRO underfloor heating also be laid on OSB boards, and how high should the screed or filler covering be?

The existing substrate must always be level, clean, dry and load-bearing.

FLEXIRO underfloor heating can be installed on OSB boards. Bostik's instructions clearly state that the OSB boards must be bonded to the substrate. Floating OSB boards are not suitable. The OSB boards must be primed before laying the FLEXIRO underfloor heating. In this case, the pipes should be covered with at least 5 mm of screed.

Can the FLEXIRO underfloor heating be retrofitted to an existing single-pipe heating system?

FLEXIRO underfloor heating cannot be connected to a single-pipe heating system.

Are the T-pieces for connecting to the existing heating system included in the kit?

The T-pieces are not included in the underfloor heating system because we don’t know which pipe dimension your existing heating has. However, you can easily obtain the T-pieces from specialist dealers.

Is the screw connection to the existing heating pipe (copper) supplied?

No, because we don’t know which pipe dimension was used on site. However, the connecting piece can be ordered individually in the Web shop under Underfloor heating accessories.

Are the FLEXIRO pipes oxygen diffusion-tight?

Yes. It is a multi-layer (5 layers) pipe made of PE-RT with an EVOH layer (oxygen-tight according to DIN 4726).

Accessories and Tools


What about spare parts for FLEXIRO underfloor heating?

All parts that form part of a FLEXIRO underfloor heating kit are also available as spare parts.

Do you also offer insulation for the floor?

The low profile underfloor heating is designed for mounting directly on the existing surface. The modernisation of an existing and already insulated floor usually does not require additional insulation of the underfloor heating. Therefore we only sell special insulation boards for bathrooms and other wet areas. Additional floor insulation can be bought at any specialist store. Once the insulation has been applied, you need to ensure a stable surface before installing the underfloor heating.

Ordering and Shipping


Is FLEXIRO underfloor heating also delivered abroad?

Most of the kits can be delivered to EU-Countries and Switzerland. Detailed information is provided here: Countries and shipping costs. If you do not find your country on the list, please use the contact form to make an enquiry. We will tell you the corresponding shipping costs in accordance with the country of destination.

Is it possible to deliver to another address or packing station?

The invoice and delivery addresses can be specified separately.

Are the wall heating elements also shipped with DHL?

No, a forwarding agent delivers the wall heating elements to you. You will be told the time window for the delivery in good time.

How will I be informed about the status of my order?

When we begin shipping the FLEXIRO underfloor heating you will receive an email with the tracking number so that you can track the shipment.

How long does it take to deliver?

Once the payment has been received, we can usually deliver in approximately 2-4 working days.

How can I pay for my order in the FLEXIRO Online Shop?

There are two possibilities: By immediate bank transfer or prepayment. The advantage of the immediate bank transfer is that the payment is made immediately and therefore the goods can be shipped immediately. With prepayment by bank transfer, 1-2 working days elapse until the payment is booked. The goods can only be shipped once the payment has been received.

Can I still cancel my order?

Yes. This is of course possible by email or telephone. In case of cancellation, please always quote the order number.

Installation Video for the Underfloor Heating Kit with Knobbed Mats

All Videos