Home / Guides / How to work out combined carpet and underlay TOG

How to work out combined carpet and underlay TOG

Working out whether a floor will suit underfloor heating comes down to one sum: carpet TOG added to underlay TOG, compared against the 2.5 limit.

Find each TOG from the datasheet

Both numbers come from the manufacturer. Carpet makers such as Cormar publish a TOG for many of their ranges, and underlay makers such as Interfloor, who own the Duralay and Tredaire brands, and Ball & Young publish a TOG for each underlay. Use the figure for the exact product, because two carpets in the same look can carry different TOG values depending on pile weight and backing.

If a carpet does not list a TOG, that is a signal to ask the retailer before you commit, rather than to guess.

Add the two together

Combined TOG is simply carpet TOG plus underlay TOG. There is no weighting and no clever formula. A 1.4 TOG carpet over a 0.7 TOG underlay gives 2.1 TOG combined. The same carpet over a 1.5 TOG comfort underlay gives 2.9 TOG combined.

Whichever way the sum lands, compare it to the 2.5 TOG limit set out by the Underfloor Heating Manufacturers Association. At or below 2.5 is suitable, above it is not.

A worked example

Say you have chosen a saxony carpet rated at 1.6 TOG and you like the feel of a thick rubber underlay at 1.4 TOG. Added together that is 3.0 TOG, comfortably over the limit, so the room would heat poorly. Keep the carpet but switch to a low-TOG underlay at 0.7 TOG and the total drops to 2.3 TOG, which passes. The carpet never changed; the underlay did the work.

Let the tool do the sum

Rather than hunt through datasheets and add by hand, our tool stores the published TOG for a growing list of real underlays and carpets. Pick your pair and it returns the combined figure, the pass or fail against 2.5, and a low-TOG alternative underlay when the total runs high.

Related

Sources: Cormar datasheets · Interfloor (Duralay/Tredaire) · Ball & Young