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The thermal resistance of a specific type of carpet or underlay is indicated by its tog rating (1 tog being equivalent to 0.1m² k/w, the S1 units for thermal resistance). The higher the Tog value the better insulator it is. So the lower the tog rating the better for underfloor heating they are. Recent research has shown that due to the open weave of most carpets they do not restrict the flow of heat from underfloor heating systems to any great degree. However carpet underlay and foam backed carpets do. When selecting an underlay/foam backed carpet for use over an underfloor heating system the tog rating should ideally be around 1.5 tog or less. As an example, listed below are underlays produced by Duralay, which have been tested for thermal resistance to BS4745 1990 and their respective tog ratings.

Product	Type	Tog Rating	Indicator
Floorwise Wonderlay	Flat Sponge (63 oz)	0.36
Silent Pro 3	Flat Sponge (90oz)	0.38
Duralay Contract 300	Contract Sponge	0.44
Eurolay	Export Latex	0.47
Duralay Contract 475	Contract Sponge	0.55
Timbermate Excel	Flat Sponge (75oz)	0.5
Duratex	Flat Sponge (75oz)	0..57
Duralay Contract 625/Floorwise Stability	Contract Sponge	0.66
Duralay President	Flat Sponge (85oz)	0.68
Duralay King	Flat Sponge (125oz)	0.80
Duralay Queen	Flat Sponge (105oz)	0.81
Durafit 500	Crumb	0.83
Flamecheck	Latex Foam	0.86
Feltex	Flat Sponge (80oz)	0.97
uintus Luxury	Export Sponge (115oz)	1.01
Super Green	Sponge (64oz)	1.01
Treadmore	Crumb	1.03
Quintus Crown	Export Sponge (80oz)	1.08
Durafit 650	Crumb	1.10
Super Duralay MK3	Crumb	1.15
Supreme	Sponge (90oz)	1.27
Gold	Sponge ((115oz)	1.31
New Gold Medal	Crumb	1.36
Bronze	Sponge (75oz)	1.37
Standard	Sponge (50oz)	1.37
Silver	Sponge (90oz)	1.43
Hallmark Supreme	Sponge (115oz)	1.51
Lifestyle Select	Sponge (115oz)	1.51
System Ten	Crumb	1.55
Platinum	Crumb	1.67
Cushion Support 600	Crumb/Felt	1.70
Olympus	Latex Foam	1.74
Triple R Silverline	RRR	1.85
New Durafelt	Felt	2.03
Homecushion	Latex Foam	2.09
Felt 42	Felt	2.44

Underlays

Duralay advise that, although none of their underlays are specifically designed for use with underfloor heating, the mid weight higher density products (generally crumbs and flat sponges) provide the best balance of properties beneficial to the carpet and the efficient operation of the heating system. Treadmore, at 1.03 togs, is suggested for domestic installations. Durafit 650, at 1.10 togs, has successfully been used in contract installations for many years.

Foam Backed Carpets

The Tog value of the carpet should be checked and a carpet selected to provide a value of 1.5 or less.

Carpets for office/ commercial premises

Carpets designed specifically for offices/commercial premises which do not have separate underlays are generally entirely satisfactory for use,however always check the Tog rating. When selecting carpets or underlays for use over underfloor heating, your carpet supplier should be advised that the heating is underfloor heating and that a low tog value is required. The carpet/underlay supplier should be able to provide the tog rating of their products and be able to confirm that their selection is suitable for this purpose.