What is carpet tog?

A 'tog' is the unit of measurement we use to show a material's - or carpet's - thermal insulating property. In short, form, the higher the tog value material or carpet has, the more it will retain heat and the better it will be at insulating. Tog is very important in the flooring world depending on your needs - higher tog will help insulate a home better, but lower tog will work better with underfloor heating. The overall tog value of a chosen flooring option will also include the underlay - so choices will often be influenced by budget and (as mentioned) underfloor heating presence.

In general, the type of flooring influences tog thus; the denser the pile construction of the carpet, and the heavier the pile weight, the greater the tog value. Tog tends to range from 0.70 to over 3.00.

Which value is best for me?

The best rule of thumb is: lower tog is good if underfloor heating is present, but higher tog otherwise will help insulate a home and keep it warm. Higher tog carpet combined with underfloor heating is no disaster - it will simply slow the heat transfer from the heating system to the room above.

Wool carpets have a higher tog rating naturally than other fibers, as do foam underlays over felts.

Other considerations, such as to the weight of the carpet, should also be considered when buying flooring.

Underfloor heating has become increasingly popular in both Retail and Commercial environments. The claimed advantages of energy efficiency combined with this obviously comfortable heat source mean 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 the 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 that 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 the 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 tile 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/leveling compound before any floor coverings are laid. This is to prevent the underlay/carpet molding itself to the levels of the shape of cables in the matting so that they can be seen on 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 double-stick installation systems are recommended to provide close contact between the floor, underlay, and carpet.