Underfloor heating

Because of its composition and construction, a Lalegno multilayer parquet floor is more suitable for underfloor heating than solid parquet. A parquet floor composed of two or more layers is also more stable than a product with one layer (solid wood). The parquet and the underfloor heating must be installed by professional parquet installers.

 

Is there a maximum width or thickness of floor plank?

There are no hard and fast rules in this area. Broad planks will, with the same percentage change, show a greater nominal movement than narrower planks, so they will also have a bigger seam in the event of shrinkage. A good rule of thumb is to take into account the width-to-thickness ratio of the plank S. We recommend a value between 8 and 11. When exposed to the same movement thinner floor components (broad and thin planks) are at greater risk of deformation than less thin planks.

Before you decide to install a parquet floor, you should first check carefully that all the criteria for correct installation of underfloor heating have been met.

Check that the floor composition is correct

Ensure that the floor has been correctly constructed and contains all the necessary floor elements, in the correct order.

  1. Wooden flooring
  2. Screed
  3. Mesh reinforcement
  4. Heating element
  5. Damp protection
  6. Heat and/or acoustic insulation
  7. Damp protection
  8. Load-bearing floor

Choose the right heating system

When installing a parquet floor on top of underfloor heating, it is essential that the maximum water temperature of the heating system is limited to a maximum of 45°C. For thermal comfort, it is also best if the surface temperature of the floor (this is not the same as the atmospheric temperature) is not higher than 25°C (max. 28°C).

Let the screed dry completely

In the case of underfloor heating and a cement-based screed, the upper limit for mass fluid content is 2%. For anhydrite screeds the maximum mass fluid content is 0.6%.

Take into account the relative air humidity

The relative air humidity on the floor surface must remain higher than 45%. 
In practical terms it is recommended to use the underfloor heating as a basic heating system, combined with convectors for peak times or rapid heating up. Underfloor heating is only recommended as a main source of heating in well-insulated buildings.

Follow the right procedure for turning on the heating

After installation of the load-bearing floor, the heating system is activated slowly and after the appropriate delay (depending on the screed). The heating system should never be used before the screed is completely dry (see also ‘Let the screed dry completely’).
The water temperature should be increased by 5°C per day until it reaches 45°C, or until the screed reaches a surface temperature of 28°C.
The heating should be turned off or kept very low 48 hours before the installation of the parquet. The surface temperature should then not exceed 15°C, while room temperature should not fall below 18°C. Both these criteria must be met. It is important that the conditions for installation are favourable and equal to a 'normal' interior climate.
The temperature should only be gradually increased 3 days after the parquet has been installed. The increase in the hot water temperature should be limited to 5°C per day maximum.

Ensure that the parquet is correctly installed

In order to ensure optimal heat transfer from the underfloor heating system to the interior environment, the parquet floor should be glued. Before gluing the parquet, check that the parquet glue is suitable for use with underfloor heating. Thermo-hardened glues achieve the best results with underfloor heating and are therefore recommended (in practice, this is usually a two-component PU glue). For advice on this, contact your Lalegno dealer. In practice most floating installations are combined with an acoustically insulating underlayer. This is a cellular material with a specific heat resistance (stationary air). This is not really recommended in combination with underfloor heating. Layers of air should where possible be avoided because they have a heat-insulating effect. If layers of air do arise, they will decrease the efficiency of the heating installation. 
A WORD OF CAUTION: After installing the parquet on top of the underfloor heating, it should not be covered with, for example, tetrapak or other materials that do not allow air and heat to permeate. This will cause heat accumulation and will lead to irreversible and irreparable damage to the floor (Lalegno painter’s fleece is not suitable for this purpose).

Heating-up protocol

Before, during and after the parquet has been installed, the heating-up protocol of the underfloor heating system must be respected. A heating-up protocol must be followed for all underfloor heating systems. A heating-up protocol should be respected from the moment the system is first used to the moment that the floor is finished and the underfloor heating is being used on a permanent basis. However, it is always important for parquet floors to keep the hot water temperature at a maximum of 45°C. Sudden variations in temperature can result in permanent damage to the parquet. Specific criteria and requirements should also be respected in the area of maximum floor surface temperatures (comfort temperature of 25°C (max. 28°C) and temperature fluctuations (crack formation). The Lalegno guarantee is no longer valid if these guidelines are not respected.
The Heating-up Protocol should be filled in and saved. Since there are a wide range of underfloor heating systems, you should contact the manufacturer of the system you have installed to obtain the appropriate heating-up protocol.
Important: when turning off the installation, the procedure should be followed in the reverse order. To minimise temperature fluctuations, avoid turning down the thermostat at night and then turning it up again in the morning.

Relative air humidity and air humidity equilibrium

Equilibrium air humidity: 55% (±10%)
Equilibrium air temperature: ± 20°C

Wood changes in response to humidity not heat. Parquet shrinks if it is dry and swells if it is wet. In contrast to most other materials, therefore, wood shrinks when heated up (due to drying out). The wood humidity adapts to its environment: in a humid house the parquet opens up and in extreme conditions it will balloon (a de-humidifier is needed in this case), in exceptionally dry conditions on the other hand, it will continue to shrink and splits will form between the planks (for this reason it is recommended to install humidifiers in the heating season). Heating dries out wood: interior rooms are drier in the winter than in the summer. There is no point in subjecting the parquet to extreme drying before installation, as there is then a risk that the parquet will burst out due to extreme swelling during a humid summer. It is therefore important to link up all the elements that play a role in the best possible way.

Finally, you should always be aware of more pronounced extremes in relative air humidity in the summer and winter, whereby cracks between the parquet elements can never be completely excluded.

The parquet installer will inform the client about these matters, and give clear user and maintenance instructions for the floor.

Conditioning of the parquet before installation

The wooden floor components should be allowed to acclimatise in their packaging in the room where they will be installed for at least 48 hours.

Wood is a natural material and can shrink or expand with variations in temperature and humidity. It is therefore essential that the underfloor heating system is operated correctly. This will prevent permanent damage to the parquet floor.

Thermal resistance

The heat from the underfloor heating is radiated to the environment. This transfer of heat occurs through the under layer and floor covering. The under layer with floor covering has a delaying effect on the heat transfer which depends on the insulation value of the materials beneath the underfloor heating. The determining factor is the heat transfer coefficient (Lambda (λ)) and the thickness of the material. This resistance can be calculated using the following formula:

The thermal resistance is expressed in R [ m².K/W]

 

where R is the thermal insulating capacity of a material layer. The material thickness, in metres, is divided by the Lambda (λ) value. The higher the value, the better the insulation.

Heat transfer coefficient of Lalegno Parquet floors: 0.14 (λ) W/mk

Thermal resistance, R values of Lalegno Parquet floors:

  • 10mm Lalegno parquet: 0.07 m².K.W-1
  • 15mm Lalegno parquet: 0.11 m².K.W-1
  • 21mm Lalegno parquet: 0.15 m².K.W-1

 

The following thresholds should be assumed for a good transfer of heat:

As additional heating: 0.18 m².K.W-1 (sum of the thermal resistance on top of the heat emission elements)

As main heating source: 0.14 m².K.W-1 (sum of the thermal resistance on top of the heat emission elements)

 

You can also calculate combinations yourself by adding up the thermal resistances (Rm values) of the screed + underfloor, glue and floor covering. By comparing these with the application thresholds, you can adapt the choice of parquet, glue or underfloor.

 

Calculate the maximum obtainable thermal release Q as follows:

To= maximum permissible surface temperature of the screed under the parquet

Rc= wheat transfer resistance of the parquet floor

Tr= room temperature

Rl= thermal resistance = 0.083

Types of underfloor heating

Wet system (pipes underneath in the screed)

In this format the heating pipes are situated in the screed (coating). The requisite theoretical transfer resistance of the screed must be between 0.10 and 0.12 m2 K/W. An important aspect is the covering of the finished layer above the heating pipes. This should be at least 3 cm for the strength and heat distribution in the floor.

Dry system (with resistors)

In this format, there are far fewer preliminary conditions than with a wet system. Insulation/polystyrene or cardboard sheets are laid on the construction floor. The heat conduction plates are laid on top and equipped with holes into which the plastic heating pipes are inserted. These heating pipes are then covered with a screed.

Electrical underfloor heating

Low voltage heating which is inserted in a thick coating or micro-concrete. There are also systems that are laid in mats on the coating. These can cause major temperature fluctuations, and are therefore unsuitable for laying under Lalegno parquet floors.

Which types of wood are suitable

Beech wood and jatoba are nervous woods that cannot be used in combination with underfloor heating. ‘Nervous’ wood types are more sensitive to humidity and are more quickly deformed. Wood should always be artificially dried to a humidity level that corresponds to the interior climate of the building, i.e. 9 to 10% wood humidity content.

Floor cooling

Floor cooling is a new trend for creating a pleasant interior temperature. In the floor cooling system, cold water rather than hot water is pumped around the pipes. By cooling the parquet, the wood humidity percentage will rise causing the wood to expand. In this case, sufficient space should be allowed for expansion to avoid damage. It is also important that provisions are made within such installations to prevent condensation from forming. Installation of floor cooling systems under parquet nullifies the guarantee and the total final liability lies with the installer.