Floor Temperature Interpretation – Know This Before Installing UFH

Underfloor heating (UFH) is now a hugely popular, appealing and potentially cost-effective source of heating, hence its increased desirability within the UK market.

The type of floor covering installation needs to be taken into consideration when designing UFH. Insulation factors of floorcoverings will obviously affect the performance of the UFH whilst some flooring installations may be affected by high subfloor temperatures and also by large fluctuations in subfloor temperatures. Subsequently, those in charge of operating the UFH should be aware that sudden large changes in subfloor temperatures must be avoided at all costs.

Types

UFH can be broadly categorised into two types: water systems and electrical systems. The majority of modern UFH systems in new build projects are warm water systems. Most systems integrate high tech plastic pipe within the floor – warm water at temperatures of 30–55°C (in general) is circulated through this pipe and this warms the floor surface to a temperature of 23–29°C (in general).

Electrical systems require the installation of a flexible heating element beneath the floor covering or underlayment which come in the form of cables, mats or film and can be installed within a standard screed or over the floor within a tile adhesive or levelling compound (minimum depth to be manufacturer recommended). These are normally a retrofit when refurbishing an existing property but are becoming more popular on new builds.

Design Considerations

Most floor coverings can be used over UFH, however this should not be taken for granted. The important principle to bear in mind is that UFH relies on the upper surface of the floor covering being warmed to a temperature of 23‑29°C, which will result in an adhesive bond-line temperature that should not exceed a nominal 29°C. However, some manufacturers within the contract flooring industry prefer to recommend a maximum adhesive bond-line temperature of 27°C. Floorcoverings and adhesives should therefore be specified and used by considering: heat output required; floorcovering and resultant floor temperatures; and manufacturers’ recommendations for all the specific products under consideration.

Floor Temperature Interpretation

The UFH industry designs to BS EN1264: Waterbased surface embedded heating and cooling systems/BS EN50559: Electric room heating, UFH, characteristic of performance, which
contains parameters for allowable floor surface temperatures.

These Standards allow for maximum floor surface temperatures of design air temperature plus 9°C in occupied areas and plus 15°C for peripheral areas, whilst some thicker floorcoverings, especially those with foamed backing layers, have a higher thermal resistance and this can result in higher interface temperatures.

In areas where UFH is used, it is recommended that agreement between the adhesive and flooring manufacturers should be obtained on the type of adhesive utilised for installation.

British Standards contain differing and conflicting information, for example:

BS 8204-1 Screeds, Bases & In-Situ Flooring, states: ‘… the usual operating surface temperature of a heated levelling screed is about 27ºC; however, some locations operate at higher temperatures, e.g., 35ºC’.

BS 8203 Code of Practice for the Installation of Resilient Floor Coverings states: ‘When used with many flooring materials UFH can cause problems if the temperature at the interface between the subfloor and flooring exceeds 27°C or is subject to rapid fluctuations in temperature. In the majority of installations this temperature will not need to be exceeded if the building insulation meets the requirements of Part L of the Building Regulations.’

BS 8425 Code of Practice for Installation of Laminate Floor Coverings and the Code of Practice issued by the Association of European Producers of Laminate Flooring states that the surface temperature should not exceed 28°C.

Whilst there are minor differences in actual temperature level recommendations, specifiers should be aware of the point that is essential, when installing floors over UFH, to consult the flooring manufacturer and adhesive suppliers for advice.

For more information, visit the free CFA Guide to Contract Flooring.

CFA members also benefit from the CFA guidance document ‘Beyond Installation – CFA Guidance on Underfloor Heating’, available exclusively in the CFA Members’ Area.