Under Floor Heating and Cooling

    • 1.


      Using Engineered wood flooring in conjunction with under floor heating is possible with most of our products (14.8, 16, 19.5 and 20mm board thickness) provided all necessary precautions have been taken to avoid tension in the lumber originating from unsuitable moisture or temperature conditions.

      When Floor heating is installed moisture content of the parquet/wood board will become lower than without floor heating. This shall be taken into consideration when parquet type, laying method and species are chosen (some species, for example Beech and Maple, may be especially sensitive to temperature changes and are therefore not suitable for this use).

      A subfloor heating system is a “slow system”: it takes longer for a room to reach the right temperature and also for the heat to leave the room again. The heating pattern of the occupants is very important: the more stable this is, the better. Too much heat causes the wood to dry out and shrink. Rapid and major fluctuations in the temperature may damage the floor. Practical matters also play a role: rugs and carpets on the floor and cupboards with no space underneath can also cause heat to build up, possibly resulting in shrinkage joints and cracks. These can be prevented with the help of one or two tips on heating and interior design. Large temperature fluctuations are not desirable for subfloor cooling either, but this will usually not be relevant here. The principle of subfloor cooling is based on cold water that heats up before it is cooled again. This heating up is achieved by removing heat from the room to be cooled. Because the temperature used is lower than that of the surroundings, there is a risk of surface condensation.

    • 2.

      Product selection.

      We recommend primarily the use of our products with 14,8 and 16mm total thickness as those have 3,8mm hardwood wear surface bonded to a multi ply poplar or birch base board. This construction greatly reduces the movement of the flooring when heat is applied and will not create too much thermal resistance.

      As the product is non-structural and therefore needs to be laid over a concrete, plywood or softwood timber sub-floor that complies to the National Standards this range is ideally suited to most environments.

      Where a structural timber is required or in areas where a solid timber sound and appearance is required we offer Engineered flooring with 19.5 and 20mm thickness boards. This product range consists of a 5,5mm hardwood wear surface bonded to 14mm birch or poplar multilayer plywood base. Due to the thickness, this timber construction has the same resonance as a solid timber floor with the stability of an engineered timber.

    • 3.

      Key parameters.

      In all cases, the sub floor should not be heated above 26°C to ensure optimum stability and thermostatic controls should never be turned up excessively as this may also permanently damage the floor system. Above 26°C the board surface may shrink opening up joints or splits may occur in the board surface due to the shrinkage in the wear layer. This does not affect the structural strength of the timber but creates small cracks which can be rectified using a hot wax.

      Other key parameters which should be respected:

      • maximum effect measured on the surface of the subfloor: 75 W/m²
      • maximum thermal resistance: 0,15 m²K/W (this is a guideline to select a wood specie and built-up that will allow a good transmission of the heating; oak board with 19,5mm thickness is at about at the 0,15 m²K/W value).
    • 4.

      The Fitting of Engineered wood flooring over under floor heating.

      It is advisable to read this entire paragraph in conjunction with the under floor heating/cooling manufacturer’s recommendations

      Engineered timber floors should be left in the area in which the flooring is to be laid for a period of 10 working days without opening the packs.

      • 4.1

        Electric heating.

        There are many electric heating systems on the market, typically using heat reflective underlay. Special consideration should always be taken when laying timber over an electric heat system. Only electric systems guaranteed to be used under timber flooring should be used as tile based systems are not suitable due to potential heat spots

        Once installed care should be taken to ensure there are no areas where the heat source can increase. I.e. rugs laid over timber flooring as this will act as an insulator and may, in time effect the timber flooring. Ensure the sub-floor is dry, flat & level (according to National Standards), ensuring the moisture content of the sub-floor is below 10%.

        Overlay with a 6mm heat reflective underlay ensuring (1.2 x 0.8, taping all joints). Lay the carbon element, a series of sheets over the floor area. Mark out and omit areas where furniture such as wardrobes, kitchen units or other heavy furniture is to be installed to prevent heat build-up. Overlay with 1000 gauge polyethylene sheeting. Overlay with timber flooring looselay to the sub-floor gluing joints with heat resistant PVA adhesive. Leave a 12mm expansion gap around the floor parameter (or 1.5mm per running metre across the width of the floor whichever the greater).

        We cannot guarantee that some of our Engineered floor products against showing slight cracking. Some wood species not particularly suitable for under floor heating are Jatoba, Ipe, Tajibo, Momoqui or Sucupira. Any floors that may suffer minor cracking can easily be rectified using bespoke hot wax.

      • 4.2

        Water heating.

        Where possible water heated systems are best suited to timber flooring as the temperature is controlled and continually flowing below the flooring giving a uniform heat source

        As water heated systems are primarily laid into a screed, the heating system should have been operational for a period of time (varying depending on screed thickness, advice should be sought from the under-floor heating manufacturer) to allow all latent moisture within the screed to evaporate prior to the timber flooring being installed.

        Moisture content of the sub-floor should be no greater than 5%, flat & level to meet National Standards. If there is any doubt in the sub-floor moisture content a surface epoxy DMP should be laid.

        The flooring can then be fitted free floating as with the electric heated system using an underlay with low TOG value. Overlay the area with underlay.

        Once fitted, lay the timber flooring at 90° to the direction of the underlay gluing the joints with a heat resistance PVA adhesive.

        Allow expansion at a rate of 1.5mm per running metre across the width of the floor or alternatively 12mm, whichever the wider. Alternatively the floor can be directly adhered to the sub-floor using Rewmar elastomeric adhesive.

        Spread a small area of adhesive using the comb supplied to the sub-floor and offer up the timber flooring. In this case the joints are left free of glue.

        Water system over joists: Our 19.5 and 20mm thick Engineered products are structural. Such boards can be laid over the water system ensuring the boards are nailed at every joist using a mechanical nailer, porta-nailer or similar.

    • 5.

      Heating up before laying the wooden floor.

      • Before you use the subfloor heating system for the first time, the sand/cement screed should be at least 42 days old. Set the temperature to 20 ºC on the first day of use, and then raise it by 5 ºC every day.
      • Ensure that the supply water temperature does not exceed 45 ºC. Maintain this maximum temperature for at least 24 hours per centimetre of floor thickness.
      • The lowering of the water temperature should also be in increments of 5 ºC every 24 hours until the water temperature reaches 20 ºC.
      • The entire heating process takes 14 days – ensure good ventilation during this period to allow moisture to escape. Check the cement screed for residual moisture after this process. This must not exceed 1,8% for a sand/cement screed and 0,3% for an anhydrite floor; if a liquid moisture barrier is used, the maximum is 3%.
    • 6.

      Heating up after laying the wooden floor.

      As timber is a hygroscopic material and will continue to expand and contract depending on climatic conditions please ensure heated systems are turned up gradually to prevent excessive movement and cracking of the floor finish.

      • When laying the floor, the screed should be between 15 and 18 ºC. Maintain this temperature for at least 5 days after laying, then you can slowly raise the temperature (1 to 2 ºC every day) until you reach the temperature you desire or the maximum permissible temperature.
      • The residual moisture in the floor must be no more than 1,8% for a cement screed and no more than 0,3% for an anhydrite floor.
      • The maximum contact temperature of the cement screed is 28 ºC. The contact temperature is the temperature of the surface of the cement screed / anhydrite floor, measured 3 heating days after setting the temperature (depending on the depth of the pipes).
    • 7.

      Heating during the season.

      • Raise the temperature very gradually at the start of the heating season, and lower it again very gradually at the end (1 to 2 ºC every day).
      • To keep the floor as stable as possible, do not create any difference in day and night temperatures
    • 8.

      Key points.

      • The RH in the room must be between 45% and 65%. Measure the RH using a well-calibrated measuring device in a non-draughty room 15 cm above the floor. NOTE: if the RH is too low, cracks may form.
      • The cover on water pipes must be at least 30mm thick to ensure a good distribution of heat.
      • The maximum contact temperature of the cement screed is 28 ºC.
      • Heat the room at a steady temperature.
      • Follow the heating protocol before, during and after installation.
      • When you begin to turn up the subfloor heating again in winter, do so gradually (raise the temperature approximately 1 to 2 ºC every day).
      • If the cement screed is uneven and/or weak, use an oak mosaic subfloor (take care not to exceed the maximum Rc value).
      • Sand an anhydrite floor beforehand with K24, remove all dust and always apply a primer.
      • If there is a chance of rising moisture, or residual moisture exceeding 1,8% (for an anhydrite floor no more than 0,3%) with a maximum of 3%, then apply 2 x PU280 crosswise to act as a moisture barrier.
      • If there is no mosaic subfloor, the cement screed needs to be of excellent quality. It is essential that 20 kg of pressure per m² be applied to each board immediately after gluing into place.
      • Use a two-component adhesive such as Lecol PU240 or something similar – ask your supplier for advice.
      • Apply the adhesive using a toothed T69 steel adhesive comb.
      • Do not place any rugs on top, or cupboards with no space underneath.
      • Cracks and shrinkage joints are often caused by insufficient RH and/or an excessively high water temperature.
      • For a subfloor cooling system, condensation protection must be installed.
    • 9.


      We guarantee a stable product and also give a guarantee against delamination, excessive deformation and cracking. Warm mark heat sensors should be installed in various locations on the subfloor. We may reject claims where these sensors have not been used. Installation should be carried out in accordance with the above instructions. The climate should satisfy the above requirements (RH between 45% and 65% measured 15 cm above the floor using a calibrated hygrometer; the contact temperature of the cement screed must be no higher than 28 ºC). The subfloor cooling system must include condensation protection. For more information on product guarantee, please refer to the relevant section in our Terms and Conditions.

    • Note: These recommendations are based upon regular testing and the manufacturer’s experience. They do not imply any guarantee since there is a multiplicity of factors that can influence the results. In the event of persistent, prolonged extreme climatic conditions dimensional changes and distortions may/will occur.
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