Underfloor Heating Explained

Underfloor Heating Explained


The two most popular forms of underfloor heating systems are:

A. Electrical matting systems

We do not recommend any electric heating matt system. Heat is transferred too quickly which originates floor failures.

B. Hot water pipe system (preferred system)

This is very similar to your central heating system. A screed is generally used to house the pipes. Before fitting the floor, all screeds must be checked so that the relative humidity of the concrete has reached 75% or below. The most accurate way to test this is by drilling into the screed and inserting plastic plugs. After 24 hours you can return to then take readings.

**Installation can only begin once the level of relative humidity has been reached, and the underfloor heating system has been fully tested and has been working for 2 weeks.

There are many brands for UFH available, make sure that you follow their instructions and advice as each system may have slightly different terms and conditions.


This should be left to qualified installers recommended by the manufacturer of the UFH system and you must have “flow” control valves to ensure that the temperature never exceeds 27 degrees C where the wood floor meets the screed or underlay. You cannot achieve this with thermostats.

Flow valves are not accurate and don’t take into account any other pipes that may be under the floor such as hot water or radiator pipes. The best way to avoid failure is to have a floor stat installed under the floor.
If your floor has an additional moisture content, the extra heat will result in delamination and floor failure.

Prior to installation, the installer/owner has the final inspection responsibility as to grade, manufacture and factory finish. The installer must use reasonable selectivity and hold out or cut off pieces with deficiencies, whatever the cause.

Use of stain, filler or putty stick for touch-up during installation should be accepted as normal procedure.

You must test the relative humidity of the environment the floor is to be laid in and also the moisture content of any subfloor or screed must be less than 4%.


  • Many types of wood flooring are suitable for use with underfloor heating (and cooling) – but not all. If in doubt, the first step is to consult a Specialist Supplier, the Timber Research and Development Association (TRADA), British Standard 8201:1987, or all three, as to the characteristics of the type in question.
  • Generally, the temperatures should not vary drastically
  • The UFH should never be turned off, just kept at a very low temperature.
  • Always try to avoid taking the floor from one extreme of heat and humidity to another within a very short time scale.
  • Ideally, the room temperature should be 20 degrees Celsius and not lower than 18 degrees Celsius.
  • The air relative humidity should be between 40% & 60%.
  • If you consistently turn the heating system on and off, to full heat from zero, this may “shock” the wood flooring and could cause lifting or the top layer of engineered boards de-laminating.
  • The maximum temperature of the wooden floor should never exceed 27 degrees Celsius to avoid excessive drying-out problems, which can cause stress on the wooden floor.
  • A word of caution – the addition of carpets on wooden floors can add considerable heat to the temperature between floor and carpet. Thus to achieve a 27 C floor surface temperature (75 W/m2 output) may require water pipes to operate at a lower temperature.


Most of the problems associated with wooden floors and UFH come from the following conditions:

  • The lack of correct heat distribution, dramatic changes in the surface temperature: HOT SPOTS.
  • High humidity in the room operating the heating above a surface temperature of 27 degrees.
  • Cleaning the floor with water and not a damp mop with the correct cleaning products.

If any of the above applies you can get the following wooden flooring reactions:

  • Warped boards
  • Engineered flooring that will de-laminate- this is the top layer coming off
  • Gaps appearing if not fitted correctly and you may also find the whole floor lifting.

The following information is for reference only and not to be treated as installation instructions. Please refer to NWFA for installation advise in the USA or Trade in the UK. We recommend that our floors are only installed by qualified and certified installers.