Floor Temperature Interpretations for Underfloor Heating

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 the UFH. Insulation factors of floor coverings 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. The following information is intended to assist the specifier to select the appropriate combination of UFH and flooring installation.

The UFH industry designs to BS EN1264: Water-based 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 floor coverings, 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 from 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. It is essential therefore, when installing floors over UFH, to consult the flooring manufacturer and adhesive suppliers for advice.

Opinions differ between the floor covering and UFH industries as to where temperatures should be measured. The 27°C “interface” limit restricts the choice of floor coverings that could be used over UFH. Improvements in product performance and system understanding allow the successful pairing of floor coverings with UFH. For example, some hardwood floor finishes are installed with a maximum floor surface temperature of 27°C.

Further information on the considerations of UFH are available in the CFA Guide to Contract Flooring. At the time of publishing this document further work was noted as necessary to review and update guidance in relation to the use of underfloor heating in combination with textile, resilient and timber products (and the adhesives or smoothing compounds used to install them). The next edition of the CFA Guide to Contract Flooring is scheduled for 2027.

Earlier this year, CFA launched a guidance document entitled ‘Beyond Installation: Guidance on Underfloor Heating’ as a benefit to its members, available in the CFA Members’ Area. This provides some additional guidance regarding underfloor heating and specifically how legislation is likely to affect the flooring industry and the whole supply chain. In particular, this guidance responded to the evolving landscape of UFH in light of the Futures Home Standard. Coming into effect in 2025, new regulations aiming to ensure that new homes built from this date will produce 75–80% less carbon emissions than homes built under the current Building Regulations are likely to be a key driver in the adoption of heat pumps in place of traditional heat sources.