8) Floor Finish

Almost any floor finish is suitable for use with underfloor heating:

  • Carpet
  • Vinyl
  • Wood
  • Tile
  • Stone

All of these can be used with underfloor heating as long as a few sensible precautions are taken. It is important to know the maximum heat output from each type of underfloor heating installation, a rule of thumb is:

  • Screeded floor finish – 100 watts per sm
  • Aluminium plates – 70 watts per sm
  • Heated void – 50 watts per sm

The supplier and the installer of the selected floor finish should be advised that an underfloor heating system is being used and for the supplier to confirm the manufacturers’ recommendations when using their products with underfloor heating.

CARPET – the recommended maximum limit for carpet and underlay when used with underfloor heating is 1.5 Tog. A thick carpet and underlay has the effect of providing an additional layer of insulation that impedes the heat rising from under the floor.

The carpet installer must use adhesive when putting down the gripper around the edge of the room and double sided tape should be used when laying the carpet. In absolutely no circumstances should nails be used in the floor when the carpet is being laid.

WOOD FLOORS – Most types of wood flooring are suitable for use with underfloor heating, but not all of them. Any wood flooring manufacturer that claims to have a product that is compatible with underfloor heating but then goes on to advise measuring heat output from UNDER the floor should be avoided. The industry standard is to measure the heat output from a wood floor across the top surface.

In order to avoid wood floors from warping or shrinking, attention must be paid to the moisture content. Kiln dried wood is completely dry at 6% moisture content. The moisture content of the wood can be checked by using a probe – most installers of wood flooring will either carry one of these with them or have access to a probe.

With any type of wood floor, the top surface temperature should not exceed 27 degC (75 W/sm). As wood floors heat up and cool down, they will expand and contract and a gap must be left around the room to allow for this.

TILE & STONE – where tile or stone is being used, in addition to confirming the manufacturer’s instructions the installer needs to be properly briefed to ensure he uses flexible adhesive. Failure to use this could eventually lead to the tile or stone splitting or cracking.

Tile and stone are very efficient heat conductors. Granite can conduct 100 watts/degC through a 20mm thick layer, while slate and marble can conduct 75 degC – 80 degC; limestone and sandstone conduct approximately 65 degC – 75 degC.

Stone or tile which is thicker than 20mm can be laid but the thicker the slab, the longer the underfloor heating system will take to warm the floor. And when the floor is being laid, provision must be made for expansion joints.

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UHMA - The trade association for surface heating and cooling.


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