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Underfloor heating has become increasingly popular in both Retail and Commercial enviroments. The claimed advantages of energy efficiency combined with this obviously comfortable heat source means it is being specified for many new homes particularly in the self-build sector and in many commercial developments.
Suitability of carpets

Most carpets are suitable for use with underfloor heating systems at the normal operating temperature of 27¢ªC, it must however be appreciated that all carpets and tiles act as thermal insulation materials and this means that carpeted floor takes slightly longer to get warm initially, but stays warm longer. The choice of underlay and installation system is also critical for best performance from the heating system. Carpets and underlays resist the transfer of heat to a lesser or greater degree and this "thermal resistance value" can be measured as a "tog" value.

Confirmed suitability testing of carpets

Recent tests carried out by the UHMA (Underfloor Heating Manufacturers Association) have confirmed that carpets perform better than had been expected with underfloor heating. Previous combined tog values for carpet and underlay tested under the 2 plate method have been shown to be higher than the tog value obtained when tested in an actual room set condition with carpet open to the surrounding air. The combined tog value of carpet and underlays obtained when tested under the 2-plate system can be lowered by as much as 1 tog to give a more meaningful result.

We always stress to our customers the need to give the information on tog values for their choice of underlay and carpet to the heating manufacturer to ensure that the heating system can perform correctly.

Types of underfloor heating systems

There are a variety of underfloor systems available and the manufacturers tend to recommend different maximum tog values

Water pipes buried in screed

With an underfloor system which uses water pipes buried in screed the maximum acceptable combined tog value of the carpet and underlay is often given as 2.5 tog or even higher. Most carpets are generally suitable for use over this type of system (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Electric heating cables buried in screed or within a suspended timber floor

These systems have a greater tendency to overheat with thicker floor coverings and for this reason a maximum tog value of 1.5 may have to be adhered to. (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Electric heating mats set on top of a structural floor

These products are generally only recommended for use under tiled or other hard floors. If however carpet/underlay is installed then suppliers of these types of matting would generally recommend that they should be covered by a flexible adhesive/levelling compound before any floor coverings are laid. This is to prevent the underlay/carpet moulding itself to the levels of the shape of cables in the matting so that they can be seen in the carpet. The maximum tog value quoted by the system manufacturer should be adhered to (We always recommend that you consult with the heating manufacturer to ensure that the carpet/underlay combined tog value is suitable for the system)

Guidelines for Installation of Carpets and Underlay

As a general rule doublestick installation systems are recommended to provide close contact between the floor, underlay and carpet .