Questions with Answers about our Heating Kits
The aim of hydronic balancing is to ensure that all heating circuits of the underfloor heating system are evenly supplied with heating water. This ensures that the system temperatures are maintained over the entire area and that the heating system can work efficiently. The German Building Energy Act even stipulates that all devices in a heating system must be hydraulically balanced. The Multibox RTL has a special thermostatic head to simplify hydraulic balancing. We have summarised detailed information on the procedure in a PDF.
FLEXIRO radiant heating systems are installed in accordance with the Tichelmann principle. The heating circuits are designed so that they have identical pipe lengths. For circuits with shorter flow pipe, the return pipe must be extended accordingly to ensure that the total pipe lengths remain comparable. This prevents shorter heating circuits from receiving more heating water and longer heating circuits with higher pressure resistance from heating up less.
With the thin 10 mm pipes, hydraulic resistance is more important than with conventional pipe diameters. To ensure that the retrofitted underfloor or ceiling heating system functions reliably with most heating systems and connection scenarios, the length of the heating circuits has therefore been limited to 30 m plus supply. The equal length of the heating circuits ensures optimum hydraulics. Hydraulic balancing is generally no longer necessary. The disadvantage is that the pipe lengths must be aligned with the longest heating circuit.
We are a manufacturer of components for ceiling heating systems. We cannot provide planning or installation services. In individual cases, however, we can put you in touch with an HVAC installation company. If you send us the key details of your modernisation project, we can match the location with our database of installers.
You are a HVAC company and would like to install FLEXIRO sets? Please get in touch with us.
The weight of the ceiling heating with plastic pipe is 9.05 kg/m² when filled with water. The copper pipe variant weighs 12.58 kg/m².
Gluing tiles onto plasterboard when using drywall panels as wall heating is possible without any problems. The manufacturer's instructions must be observed. Double planking may be advisable when using heavy tiles. Tiles are suitable as a surface for wall heating in the bathroom or kitchen due to their good thermal conductivity.
In most cases, it is possible to install wall heating in drywall construction on an existing plasterboard wall. A second layer of plasterboard can be glued on using gypsum blocks. Apply the gypsum blocks at 30-40 cm intervals. The additional planking should be installed offset from the first layer. The joints must not overlap. Please note, due to their outer diameter of 22.5 mm connectors require a corresponding cavity into which they can be inserted.
For structural calculations in the run-up to a house modernisation, it is sometimes necessary to know how much weight the underfloor heating will put on a floor. Of course, the weight depends on the individual floor structure and the materials used. Nevertheless, the weight of the FLEXIRO components can be calculated. The majority of the additional weight is attributable to the levelling compound. The specific weight of a levelling compound is typically between 1.6 and 1.8 kg/m² per 1 mm layer thickness. With a construction height of 17 mm, an estimated weight of approx. 26 kg/m² can be expected. The underfloor heating itself adds only approx. 1.9–2.2 kg/m², even when filled with water. Therefore, the thin-layer system is much lighter than a standard underfloor heating system where the heating screed must be included in the calculation.
The minimum coverage for the heating pipes is 3 mm. However, the required layer thickness depends on the flooring material selected. The minimum layer thickness is only recommended for tiles and ceramic materials. Other flooring materials require an additional 5 mm of coverage. The levelling compound must be flexible and bear the manufacturer's mark indicating suitability for thin-layer underfloor heating. To ensure optimum heating and cooling performance, apply the levelling compound as thinly as possible. Further information on the thermal resistance of standard floor coverings can be found in our underfloor heating data sheet.
The wall heating elements can also be installed horizontally. This may be necessary if there is limited space on the wall due to windows, for example. In such cases, a combination of vertical and horizontal elements is possible. Also wall and ceiling heating elements can also be combined. Ensure that the heating circuits are of a uniform length and that the permissible bending radius of the supply lines is observed.
Definitely not. The FLEXIRO underfloor heating system is designed precisely for this application. The diffusion-tight 10 mm PE-RT heating pipe minimises the risk of corrosion in the existing heating system. The RTL control boxes prevent high hot water temperatures, which can be a problem for the underfloor heating circuits, by limiting the return temperature. Radiators and underfloor heating can be safely combined in mixed operation with this technology.
The term low profile underfloor heating refers to extremely flat underfloor heating systems that do not require a heating screed and can therefore be realised with installation heights of 20 mm or less. There are specific advantages and disadvantages associated with thin-layer systems which determine the areas in which they can be used.
Benefits
- Due to the low installation height, thin-layer systems can be retrofitted on the existing floor surface. The installation height is below the height of door thresholds in old buildings, for example. Thermal insulation is only required for floors that do not have minimum thermal insulation. The design considerably reduces the work involved in retrofitting underfloor heating.
- The position of the heating pipes directly under the floor surface enables particularly rapid heating behaviour with even heat distribution.
- The low flow temperatures ensure noticeable savings in heating costs.
- The absence of an additional heating screed and the low weight of the thin underfloor heating reduces the load on the ceiling below.
Disadvantages
- The low height is achieved by using thin heating pipes, which have a comparatively high flow resistance. This limits the length of the heating circuits, which means that in larger rooms, several circuits must be installed that do not differ significantly in length.
- Floor slabs above basements or the ground, which have a high thermal resistance, must also be insulated. This cancels out the advantage of low installation height. Without thermal insulation, the heat output of a low profile underfloor heating system in energy-saving mode may not be sufficient to dissipate enough heat into the room in the case of external floor slabs.
- The levelling compound must not be applied too thickly so that the heat output can be provided close to the surface.
In principle, installations that deviate from the standard drywall kits are possible, e.g. if there is not enough space for the standard number of drywall panels and the next smaller heating kit is too small. In such cases, it is advisable to ask our technical support team for an assessment of the planned project. We will check the feasibility of the project and put together a customised quotation.
In our experience, the 12.5 mm plasterboard is also strong enough for use in pitched roof applications. Thicker boards are not required even in damp rooms or in the wall heating version with copper pipe. As always, the manufacturer's specifications should be consulted when planning specific applications. Further information on the thermal activation of pitched roofs.
The amount of levelling compound required for low profile underfloor heating depends on the specific weight of the levelling compound. This is stated on the packaging and is usually between 1.6 and 1.8 kg/m² per 1 mm layer thickness. A specific weight of 1.6 and a layer thickness of 17 mm including underfloor heating results in a consumption of levelling compound of 25.9 kg per m². The recommended laying distance of 100 mm was assumed.
No RTL valve is required when connecting the radiant heating to a heating circuit manifold. As with the standard sets, the connection is made using the manifold fingers. The manifold finger is screwed onto the heating circuit manifold using the matching union nut. Ask our technical support for set prices without RTL box.
This is possible in principle. However, it should be noted that wood deforms when exposed to moisture. Plaster, on the other hand, is a rigid system. Plaster manufacturers therefore recommend the use of carrier boards. Plaster manufacturers will provide detailed instructions for the specific application.
A suitable hose fitting is required to connect the pressure test pump to the RTL box.
A pressure test should always be carried out before commissioning the panel heating system. We have summarised how to connect the pressure test pump to the RTL box, information on the test pressure and the correct procedure in a short video:
Pressure test of a panel heating system [Text in German]
The control of the heating temperature via the RTL principle (=return temperature limiter) is an established control technique. It is particularly suitable if the new radiant heating is to be integrated into an existing heating system with higher flow temperatures. The RTL valve permanently measures the heating water temperature in the heating circuit. If this is too high for a radiant heating system (the limit is about 45°C), the valve interrupts the flow through the heating circuit and no further hot water flows into the heating circuit. Thus, the water in the heating circuit then cools down again. If the temperature falls below the maximum temperature of the radiant heating, the RTL valve opens again. Further details on how they work can be found directly on the product pages of our RTL boxes.
If there is an unheated room above the planned ceiling heating and the old ceiling has no thermal insulation or the heat transfer coefficient of the ceiling is unknown, we recommend installing an additional layer of insulation. In any case, thermal insulation above the ceiling heating will improve the response time of the heating.
The thermostatic head in the Multibox 4K-RTL can be replaced by a Smarthome servo drive. The retail market offers various brands for this purpose, depending on the Smarthome system. The product to be selected must have a connection thread of M30x1.5 and have the corresponding adapters for the IMI thermostatic head K installed as standard in the Multibox.
FLEXIRO's preassembled kits have the advantage that all the included components are technically harmonised with each other, ensuring that the radiant heating system will function perfectly in most installation situations. Of course, if you have the appropriate expertise or are supported by a heating engineer, the components can also be installed differently to the set design. For instance, the FLEXIRO radiant heating system can be connected to a standard heating circuit manifold. If required, our sales department will be happy to provide a quote for customised sets or sets without an RTL control box. Please note that we cannot accept any responsibility or guarantee the proper functioning of the heating system for solutions that deviate from the set design.
The substructure for the ceiling heating should fulfil the dry construction guidelines for suspended ceilings. When using CD profiles and direct hangers, a suspended height of approx. 5 cm can be used for planning. A small distance to the bare ceiling is required for looping through the FLEXIRO connection pipes and plug-in connections. The dry construction guidelines also permit the use of wooden battens as a substructure for the plasterboard panels. However, their dimensional accuracy and torsional rigidity is usually less good compared to CD profiles made of sheet metal.
Yes, the FLEXIRO wall heating can be installed on an external wall. However, the external wall should have a maximum U-value of 0.30 W/m2K. If insulation is fitted behind the wall heating in order to minimise heat loss to the outside, it may be necessary to check the building physics of the construction. It should be checked that no condensation occurs in the wall when the wall heating is not in operation. During operation, the wall heating will heat the activated wall dry rather than causing moisture damage to the construction.
The components of the FLEXIRO sets are harmonised in terms of their technology. It is very unlikely that the heating pipes will not allow enough heating water to pass through if they are installed correctly. If the heating surface does not heat up, this is usually due to the following causes:
- Please check whether the RTL box is correctly connected to the flow and return of the heating system.
- A kink in a heating pipe. The kink is cut out and the ends of the heating pipes are securely connected with a plug connector.
- When installing several heating circuits, a heating pipe has been shortened disproportionately 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 length.
Before applying plaster or a levelling compound, it is essential to carry out a pressure test on the radiant heating system in order to identify and easily resolve such problems.
The heating capacity of the radiant heating kits depends on the application, installation distance, insulation and floor covering, etc. The information in our technical data sheets provides data on the average heating capacities of our kits.
Combining underfloor heating with ceiling or wall heating elements is generally possible, provided the following technical requirements are met: The maximum of four heating circuits and the maximum length per heating circuit of approximately 30 metres must not be exceeded. Differences in length between individual connections should not surpass 15% Otherwise, there could be problems with the hydraulics. We will be happy to provide you with a customised quotation for combinations of ceiling, wall or underfloor heating systems within the scope of these planning specifications.
Yes, if a structure with wooden beams as shown in the installation instructions is not possible, e.g. due to a small room size, the plasterboard panels with integrated heating pipe can also be glued directly to the wall in accordance with the drywall construction guidelines. According to the manufacturer, the connectors required for the heating pipe are suitable for grouting and adhesive compounds. We strongly recommend carrying out a pressure test before the bonding process.
Due to the installation as low profile underfloor heating directly under the surface, additional thermal insulation underneath the heating pipes can be avoided in many cases. This keeps the installation height low. Exceptions are floors above unheated cellar rooms or directly above the ground. The requirements of the Energy Saving Ordinance must be observed. Detailed information on thermal insulation.
Yes. Before the plasterboards are fitted, the arrangement of the heating pipes can be clearly seen on the back. A normal cavity box for holding a light switch has a diameter of 68 mm. The heating pipes have a distance to each other of approx. 90 mm. The opening for the switch should be pre-drilled from behind before mounting the drywall elements.
After installing the drywall panels, you can visualise the arrangement of the heating pipes in heating mode using a thermal camera. The pipes have a spacing of approx. 100 mm. This means that paintings or pictures can be attached to the thermally activated wall at a later date. Alternatively, the walls can be sprayed slightly damp in heating mode. If the walls are not tiled, the moisture will dry off more quickly where a heating pipe runs.
A standard 12 mm thick plasterboard is generally used for FLEXIRO drywall heating. For damp rooms, drywall construction recommends an impregnated gypsum plasterboard GKBI. More detailed information on sealing and possible alternatives can be found at www.homedit.com/bathroom-drywall. For some time now, we have also been offering GKBI wet room plasterboard for wall heating kits in dry construction.
Of course, several FLEXIRO sets can also be installed in a larger room and controlled via a corresponding number of RTL valves.
Installation plan for a low profile underfloor heating system in a 32 sqm room
In the bathroom, there are many surfaces on the floor that can remain thermally inactive because they do not efficiently transfer heat to the room anyway. This is the case under the bathtub, for example. If you exclude this area from the underfloor heating, then a 5 m² set is already sufficient for an 8 m² bathroom.
Instructions for installing an underfloor heating in bathrooms
An RTL valve is required for connection to heating systems that feed water into the circuit at a flow temperature of up to 65°C. RTL stands for return temperature limiter.
The Multibox 4K-RTL limits the return temperature and has a flow shut-off including a vent valve and a regulating spindle with which hydraulic balancing can be carried out.
It is controlled without additional energy and can be individually adjusted using the thermostatic head supplied. This functions as a continuous proportional controller. The change in the room air temperature (controlled variable) is proportional to the change in the valve stroke (actuating variable). If the room air temperature rises, the temperature in the temperature sensor expands and acts on the corrugated pipe. This throttles or increases the water supply in the underfloor heating circuit via the valve spindle.
Even if the heat generator is to be replaced at a later date with a modern heat source with low heating temperatures, such as a heat pump, the Multibox 4k-RTL can still be used. Because the flow temperature will then be moderately below 45°C, the Multibox will not have to regulate and you can continue to use the actuator. Our alternative RTL box, the Kompabox RTL, is not suitable for this.
The Kompabox RTL is used exclusively in conjunction with conventional heating systems with high flow temperature. The Multibox can also connect to radiant heating systems with lower flow temperatures. Check our comprehensive head-to-head comparison of RTL 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"
Yes, it is possible to use the ceiling heating kit for cooling in summer. Sufficient cool water supply is required though. Further details can be found at: How to use a ceiling heating as cooling ceiling.
Particularly when modernising existing buildings, there is often a lack of headroom when installing underfloor heating. Traditionally installed underfloor heating has a construction height of 100 mm and more. The old floor has to be completely removed and disposed. This results in additional costs and considerable labour. Milling grooves into existing concrete floors is also labour intensive and requires special milling machines. In addition, milling in underfloor heating is only possible if the floor slab is structurally sound enough. This is not economical, especially for small heating areas.
Our low profile underfloor heating kit, with an installation height of just 17 mm (without floorcovering), is therefore a comparatively cost-effective choice for modernising small heating areas and individual rooms in particular. There are also a number of reasons for retrofitting thin-layer systems when it comes to heating comfort.
The height of the studded plate and clip rail with heating pipe is equally 14 mm. The levelling compound is added according to the manufacturer's instructions. The covering with the levelling compound should be at least 3 mm with a ceramic surface covering (tiles etc.). This results in a minimum total installation height of 17 mm without surface covering. Data on other surface coverings in our technical information.
The surface covering has a significant impact on the energy efficiency and response time of low profile underfloor heating systems. Where possible, select materials with good thermal conductivity respectively low thermal resistance. Ceramic tiles are particularly suitable. Materials such as cork, wooden floorboards and parquet, however, take longer to warm up and require higher flow temperatures.
Table showing the heating values for underfloor heating with different surface coverings
Most of the heating kits can be delivered to EU-Countries, the UK 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 find out whether shipping to your address is possible and calculate the costs.
We also offer most FLEXIRO heating set components as spare parts in our shop. Should you require any additional stud plates, clip rails or distributor fingers e.g. which are not part of our catalogue, please contact our support team.
In our webshop, we have put together radiant heating sets that can be used especially for modernising smaller areas. This makes it easy to plan a retrofitted radiant heating system. We will be happy to advise you on larger projects or projects that are not covered by standard installations.
Billing and delivery addresses can of course be entered separately. When delivering to a packing station or post office, please enter the postal number together with the number of the packing station or post office in the field for the street.
No, the plasterboards in the drywall kits are delivered by a forwarding agent. The delivery time window will be communicated by telephone in advance. Please provide a telephone number when ordering.
Once an order has been placed, a confirmation will be sent detailing the products purchased and the delivery address. If payment is made in advance, a payment receipt will also be sent. As soon as the order has been notified to the shipping service provider, the customer will receive a dispatch confirmation with a tracking code to track the shipment, as well as a PDF invoice.
After receipt of payment, the delivery time for the ordered sets and articles is approx. 2-4 working days. Sets sent by forwarding agent may take a little longer.
The existing subfloor for the underfloor heating must be load-bearing, level, clean and dry.
This is generally possible, but care must be taken to ensure the subfloor is stable, level and dry. Any loose wooden planks should be screwed down beforehand. The subfloor must not give way or spring. When using dry screed boards, two bonded layers should be used. The board manufacturer's additional instructions must be observed. Floating wooden constructions are not suitable as a substrate because they are highly vulnerable to deformation. Therefore, underfloor heating can only be installed on connected wooden structures that are decoupled. Our support team will be happy to provide additional advice on installing thin-layer systems on floorboards.
The existing subfloor must always be level, clean, dry and load-bearing.
Once this requirement has been met, FLEXIRO underfloor heating can also be laid on OSB boards. However, according to the specifications of one of the leading manufacturers of construction adhesives, Bostik GmbH, the OSB boards must be connected to the subsurface. Floating boards are not suitable. The OSB boards must be primed before laying the FLEXIRO underfloor heating. In this case, the heating pipes should be covered with screed by at least 5 mm.
In a single-pipe heating system, the radiators are connected in series to a ring pipe. A circulation pump ensures that hot water can flow through all radiators. As this technology does not allow our control box to be installed in parallel between the flow and return pipes, a special control box is required for connection to a single-pipe heating system. Describe your heating system and your project to our technical support team so that we can prepare a customised quotation.
The T-pieces are not included in the heating kits, as we cannot know the pipe dimensions of your existing heating system. You can easily obtain the T-pieces from specialised dealers.
No, because the suitable compression fitting depends on the pipe dimensions of the existing heating system. However, we offer a selection of compression fittings in our webshop.
In many cases, thin-bed underfloor heating can be installed directly on top of an existing floor covering. Therefore, modernising an already insulated floor with thin underfloor heating usually requires no additional insulation. At FLEXIRO, we only sell special impact-resistant insulation boards for damp rooms. If floor insulation is required in certain situations, e.g. above ground or above garages, it can be purchased from specialist builders' merchants. Once the thermal insulation has been applied, a load-bearing surface must be created before the thin-layer system can be installed.
Yes, it is a multi-layer (5 layers) PE-RT heating pipe with an EVOH layer (oxygen-tight in accordance with DIN 4726). This ensures corrosion protection in mixed operation with conventional heating systems with metal pipes. The abbreviation PE-RT stands for polyethylene of raised temperature resistance. Pipes made from PE-RT are flexible and can be securely connected to each other using both plug connectors and plastic welding. The smooth surface of the inner pipe walls prevents calcification or silting. They are used for hot water installations in accordance with ISO 10508.
Currently, payment can be made via PayPal, cash on delivery or bank transfer/prepayment. Orders paid for via PayPal or cash on delivery are processed immediately and dispatched promptly. Orders paid for via prepayment will only be processed once payment has been received. Delivery of the goods will be delayed accordingly.
Yes, this is possible by e-mail or telephone in accordance with the cancellation policy. Please always indicate the order number in the case of cancellation.
The basis for entitlement to a subsidy for radiant heating is always the installation of a low-temperature heating system. The BVF Bundesverband Flächenheizungen und Flächenkühlungen e.V. (Federal Association for Surface Heating and Cooling) provides expert and up-to-date information on subsidy measures. https://www.flaechenheizung.de/foerdermoeglichkeiten/