Retrofitting Underfloor Heating in Old Buildings
Living in an old building but with modern heating
"Proper heating" or "best heating" are among the trending topics of recent years. This subjective impression is confirmed by a look at Google Trends. It should be comfortable, but energy efficient and environmentally friendly. The trend for heat sources in new buildings is towards heat pumps. In terms of heat distribution systems, underfloor heating is leading the way, as its low flow temperatures make it particularly compatible with heat pumps. The German Association for Surface Heating and Cooling estimates that 80-90% of new detached and semi-detached houses will have underfloor heating. The lion's share of these will be water-bearing underfloor heating systems.
The challenge of energy modernisation in existing buildings
In 2022, 49% of homes were still heated with gas and 25% with oil. The heat pump has a share of 3%.
The high investment costs of upgrading the entire heating system, the lack of thermal insulation and the limited possibility of using the flats while the work is being carried out prevent many owners from converting the heating system to underfloor heating. From an environmental point of view, this means that the "heating turnaround in existing buildings" falls far short of the targets set by the German government for the building sector in order to achieve the climate targets. From the point of view of the owner or tenant, this means an unnecessary sacrifice of modern heating comfort.
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 old buildings if investing in a new heat source is not an option? The FLEXIRO solution allows the gradual introduction of underfloor heating in existing buildings. The heating kits can be installed in rooms where thermal comfort is particularly important. There is no need to replace the heating source. It can also be connected to heating systems with high flow temperatures via return temperature limiters.
Retrofitted underfloor heating can either replace existing radiators or be used in addition to radiators where thermal insulation is poor. In this way, the thermal comfort of underfloor heating can be retrofitted in a targeted manner and the modernisation of the heating source can be prepared by gradually introducing panel heating.
calculate
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
The minimum installation height of FLEXIRO underfloor heating is 17 mm. The low height of the underfloor heating means that it can be installed on top of the existing floor. Whether directly on a floor board or on an existing screed, this option minimises the work involved. In some old buildings, this is the height of the door threshold. A high quality parquet floor can then be laid over the underfloor heating.
Laying the 10 mm thin heating pipe in tight loops directly under the floor surface also provides excellent heating values and rapid heating up of the underfloor heating. The effect of the radiant heat is fully utilised thanks to the even heating of the floor.
This is how to install underfloor heating with studded panels
Drywall, clip rail or studded plates?
Drywall
add_circle
Dry construction is fast, clean and introduces little moisture into the room. As a result, follow-up work can be completed quickly and the space returned to use.
highlight_keyboard_focus
The dry screed boards are relatively heavy and potentially fragile. Two people are required to install them. The manufacturer Fermacell recommends a three-layer structure.
Clip rail
add_circle
Mounting with clip rails is particularly recommended for mounting on uneven floors such as wooden floors. It is also the least expensive of the three options.
highlight_keyboard_focus
The loops of the heating pipes may also need to be secured to the floor with dowel hooks. Otherwise the pipes could float, requiring additional grouting. This increases the cost and height of the installation.
Studded plate
add_circle
If the subfloor is smooth, the heating pipes can be fixed to the floor with stud plates. This minimises the amount of levelling compound required. This saves costs and reduces the reaction time of the underfloor heating.
highlight_keyboard_focus
The existing floor must meet the requirements for full-surface adhesion of the studded plates. Unevenness and residual moisture will affect the adhesion of the panels.
Underfloor heating systems
question_exchange
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.
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.
Such a combination is possible as long as the max. number of 4 heating circuits is not exceeded. In addition, it must be ensured that the differences in length between the individual connections does not exceed 15%. Otherwise there could be problems with the hydraulics. For combinations of wall and underfloor heating systems within the scope of these guidelines, we will be happy to submit an individual offer. Please contact our technical support.