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Underfloor Heating

Underfloor heating based on electricity or hot water loops is, in many ways, the ideal solution. Your choice of underfloor heating system should provide efficient and even heat distribution over the entire floor area.

The surface temperature of the floor must never exceed 27°C. This also applies to areas next to radiators and elements, under furniture and carpets, etc. With good furnishing and without too many carpets, or carpets that are too thick, it is reasonable to achieve a temperature of 23°C over the entire floor area, for a room temperature of around 21°C. Of course, this is assuming that the room requires a normal amount of heating. This means that your sealing, insulation, windows, etc., must be of regulation standard quality. Extra precautions should be taken to ensure the temperature at the feeding of the hot water never exceeds the maximum level, and that installation instructions provided by the supplier of the heating system are followed correctly.

Words of warning

Floors with underfloor heating are more susceptible to moisture than those without. This is because the difference in moisture content between the driest and dampest parts of the floor will increase over time. Underfloor heating can cause extensive drying, which makes the wood contract and shrink. In a cold, dry climate, you can expect to see gaps between strips and slightly concave boards from time to time. We recommend Kährs Original 15 mm parquet flooring or Kährs Linnea 7 mm with Woodloc® or Woodloc® 5S joints for floors with underfloor heating. Both Kährs Original and Kährs Linnea reduce the risk of gaps forming.

It is worth bearing in mind that parquet flooring made from Beech and hard Maple expands and contracts more than other wood species and is therefore not recommended for use with underfloor heating.

Installing over underfloor heating

Your wood floor must be laid close to the subfloor and without an air gap, as air gaps can cause the wood to dry out very quickly.

When laying a floor over underfloor heating loops, the working temperature should be at least 18°C. This is applicable to boards, subfloors and room temperature. The relative humidity (RH) of the air must be between 30 and 60% before, during and after laying the floor.

Cardboard is preferred for the intermediate layer, as polyethylene cellular plastic and cork particleboard have a higher thermal resistance.

Find out more about installation over underfloorheating:
Subfloor Requirements and Underfloor Heating (pdf)

Special requirements when installing underfloor heating:

• The floor construction must have a heat-distributing layer that gives an even temperature over   the   entire surface of the floor area, in order to prevent high temperatures in certain spots.

• It must be possible to control and limit the surface temperature with a high degree of accuracy.

• The entire floor area must be heated. However, this does not apply to comfort heating systems,   which complement normal heating. In this case, the temperature should be considerably lower   than   the permitted 27°C floor surface.

• The laid floor - including the intermediate layer - must have a low thermal resistance.

• A vapour barrier must be built into the floor construction, positioned as close as possible to the   wood floor. It is particularly important to have the vapour barrier near to the wood floor if the joists   are thick or heavy. Under no circumstances may the vapour barrier be placed on the opposite side   of  the joists.

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