introductory price
-10%
Retrofitting Underfloor Heating in Old Buildings
Living in an old building, heating in a modern way
In recent years, the topic of heating has become significantly more important. While demand for heating comfort is growing, energy costs have also risen rapidly. This is why the demand for new heating systems is usually for systems that are comfortable, energy-efficient and environmentally friendly.
Although 80–90% of new detached and semi-detached houses have radiant heating systems, particularly water-based underfloor heating, the response to the challenges of the energy transition has been much more cautious in existing buildings. Old buildings are characterised by high ceilings, large windows and wooden floors. While these features contribute to a high level of living comfort, they can result in disproportionately high heating costs when wood and coal stoves are replaced with gas or oil heating systems, especially since thermal insulation in old buildings is usually inadequate.
While there are many arguments in favour of installing ceiling or underfloor heating in old buildings, many owners are put off by the high cost of replacing the entire heating system. FLEXIRO's low profile underfloor heating offers a solution that increases heating comfort and saves energy costs room by room without replacing the central heat source.
Does it make sense to retrofit underfloor heating without replacing the heat source?
How can the comfort of underfloor heating be retrofitted in existing and older buildings if investing in a heat pump is not an option? The FLEXIRO solution makes it possible to implement radiant heating in existing buildings step-by-step. The heating kits can be installed specifically in rooms where thermal comfort is particularly important. It is not necessary to replace the heat source. The connection can also be made to heating systems with high flow temperatures using return temperature limiters. Depending on the design, the cost of underfloor heating ranges from €75/m² to €175/m² if you do the installation yourself.
Retrofitted underfloor heating can either replace existing radiators or, in cases of poor thermal insulation, be operated in addition to the radiators. This allows the thermal comfort of underfloor heating to be retrofitted in older buildings and prepares the heating source for modernisation by introducing radiant heating gradually. Once the heat source has been replaced, the previously retrofitted heating surfaces can be connected and controlled via a heating circuit distributor.
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Calculation of the heating surface
Depending on the room conditions and heating requirements, a heating surface of 60 to 85% of the room area should be planned for underfloor heating.
Kitchen units or other storage areas should be left out during installation. For example, 10 m² of underfloor heating can provide sufficient heat for rooms between 12 and 16 m².
What makes low profile underfloor heating so attractive
FLEXIRO underfloor heating has a minimum installation height of 17 mm. This low-profile system can therefore be retrofitted onto existing flooring. Whether installed directly onto floorboards or existing screed, its flat design reduces installation costs. In some older buildings, the installation height is the same as the door threshold height. High-quality parquet flooring can then be laid over the underfloor heating.
Installing the 10 cm thin heating pipe in tight loops directly under the floor surface enables excellent heating performance and rapid heating-up of the system. Even heating of the floor allows the radiant heat effect to be fully utilised.
This is how to install underfloor heating with studded panels
Installation on OSB, on plasterboard, with clip rails or studded panels?
Plasterboard
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Installation in drywall construction using milled Fermacell gypsum fibreboards enables a quick and clean process. The handy size of the boards allows the heating surface to be adapted to most room geometries. The low layer thickness of the filling compound significantly reduces the drying time and contributes to the overall very short installation times. The floor covering can be laid the very next day. The screed panel is load-bearing, moisture-regulating, resistant and non-combustible.
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The milled dry screed panels require a level and stable substrate. The manufacturer Fermacell recommends a multi-layer structure for non-load-bearing floor constructions. The cost per square metre is comparatively higher for the dry system. Edge panels must be cut to size yourself.
OSB-Board
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OSB boards are a popular choice of material for interior construction. The wood fibre board is robust, easy to handle, moisture-resistant and heat-retaining. The milled structure reduces the amount of levelling compound required and thus the weight load from the underfloor heating. Installation is quick and the heating is ready for use after 1-2 days. OSB enables drywall construction at a comparatively low cost.
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When laying with OSB boards, an additional adhesive primer must be applied. An uncoupling mat is also required. When using on wooden beam ceilings and other floors that are not load-bearing, a multi-layer structure must be planned to ensure sufficient stability and load-bearing capacity.
Clip rail
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Mounting underfloor heating with clip rails is particularly recommended for retrofitting on uneven surfaces such as wooden floors. Clip rails allow for a low installation height and are also the most cost-attractive installation method.
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The installation effort is slightly higher than with drywall variants. In some cases, the loops of the heating pipes must also be fixed to the floor with dowel hooks. Otherwise, the pipes may not lie flat on the floor, which will require additional grouting compound. This would increase costs and installation height. Installation with clip rails requires the most levelling compound.
Studded plate
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If the subfloor is even and smooth, the heating pipes can be fixed close to the floor using studded panels. Studded panels simplify the installation of the heating pipe and require less levelling compound. This saves costs and reduces the response time of the underfloor heating. Studded systems allow you to choose any installation design you like.
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The existing floor must meet the requirements for full-surface bonding of the studded panels. Unevenness and residual moisture have a negative effect on the adhesion of the panels.
Underfloor heating systems
introductory price
-10%
introductory price
-10%
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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.
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.
Compared to conventional underfloor heating systems, low profile underfloor heating requires significantly less levelling compound.
The amount of levelling compound required for thin underfloor heating depends on the specific value of the selected grouting compound and the layer thickness. The specific value is stated on the packaging and is usually between 1.6 and 1.8 kg/m² per 1 mm layer thickness. With a specific value of 1.6 and a layer thickness of 17 mm including underfloor heating, this results in a consumption of levelling compound of 25.9 kg per m². The recommended laying distance of 100 mm was assumed.