Underfloor heating and wood floors – things to know — Installer OnlineInstaller Online

Underfloor heating and wood floors – things to know - Installer OnlineInstaller Online

Underfloor heating and wood floors – things to know

Electric underfloor heating and hydronic underfloor heating are well suited for use with almost all wood floors. Even though installing the system under wood floors requires some consideration to ensure that it operates efficiently, the system is a great addition to this natural floor finish.

Maximum 18mm thickness, density of wood flooring and insulation

Wood conducts less heat than stone or tiles, so the thinner the wood flooring is, the higher the heat output of a floor heating system and the faster the heat-up time. For an efficient heat output, the maximum thickness of the floor boards should not exceed 18mm. Floor boards thicker than this can be used with an underfloor heating system. but this will result in a lower heat output.

The density of the wood floor is also an important consideration as this influences the heat transfer. High density wood floors transmit heat better and are best suited for a use with an underfloor heating system.

Insulation should always be used with a floor heating system and wood floors as it reduces the heat-up time and keeps running costs to a minimum.

Underlay with floating and nailed floors

Floating and nailed floors require a specialist wood floor underlay over the heating system. The maximum TOG rating for everything above the heater, including the floor boards, should not exceed 2.5 as any higher than this will restrict the heat output. The underlay needs to be thin and not the foil-reflective type.

Humidity and moisture content of floor boards

The moisture content of the material is an important consideration as the humidity of the room combined with the moisture content of the floor boards determines efficient operation of the system.

Engineered wood is more stable than solid wood, but it’s important to note that the moisture content needs to be sufficient with both types. This is usually between 10-11% when the boards are laid, reducing to 8-9% when heated. It is advisable to check with the flooring manufacturer to ensure that the wood is transported, stored and installed in the correct environment.

Air humidity should be maintained between 40-60% at all times as variations in humidity levels can lead to shrinkage and expansion with wood flooring.

Installation onto cement screed subfloors

Cement screed subfloors need to have a moisture content of less than 3% and a relative humidity (ErH) of less than 75%. Anhydrite must have a moisture content of less than 0.3%.

Measurements for the moisture content can be taken 48 hours after any heating systems and dehumidifiers have been switched off and if the moisture levels are not correct, fast dry and rapid set screed and self-levelling compound can be used to accelerate the time taken to achieve the correct moisture levels.

Installation onto Joist & plywood subfloors

If you are fixing plywood to joists, the plywood needs to be a minimum of 18mm thick and screwed to the joists at 300-400mm centres. The sheets must have a moisture content of less than 10%. All sheet joints should be laid in a staggered brickwork pattern and they must not be joined at door thresholds, but a single sheet must traverse the threshold.

Maximum 27°C floor temperature

Finally, a top temperature restriction of 27°C should not be exceeded with wood floors. This is secured by using a thermostat with a floor probe that automatically controls underfloor heating so that the floor temperature does not exceed the 27°C.


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