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Underlay for underfloor heating: what to buy
For a heated floor you want a low-TOG underlay, often around 0.4 to 1.0 TOG, so the carpet plus underlay sum stays at or below the 2.5 limit.
Buy for TOG, not for plushness
The instinct in a carpet shop is to squeeze the underlay samples and pick the softest. Over underfloor heating that instinct works against you. The soft, thick, warm underlays are the high-TOG ones that block heat. What you actually want is a lean, dense underlay with a low published TOG that lets heat pass and leaves headroom for your carpet.
Look for a stated TOG on the datasheet and, ideally, an underfloor-heating or low-TOG label. Interfloor, who make the Duralay and Tredaire ranges, and Ball & Young publish these figures.
What good looks like on paper
A suitable underlay is often in the 0.4 to 1.0 TOG region. Paired with a typical carpet around 1.0 to 1.7 TOG, that keeps the combined figure at or under 2.5. Anything advertised on comfort and warmth, especially thick crumb-rubber at 1.5 TOG or more, is likely to push a carpet over the limit and should be avoided for heated floors.
Check the pair before you order
Do not buy the underlay in isolation. Add its TOG to your carpet TOG and confirm the total is 2.5 or less. Our tool lists real underlays with their published figures and does the sum against your carpet, so you can shortlist the ones that pass before spending anything.
Once you have a shortlist, an eBay or trade search for a low-TOG underlay suited to underfloor heating will bring up the products to compare on price.
One last check with the installer
Buying the right underlay puts the floor in suitable territory, but the installer commissions the system and sets the flow temperature. Confirm your final carpet and underlay with them before ordering, so the room heats as you expect and nothing runs hotter than it should.
Shortlist a low-TOG underlay that passes
Open the underlay TOG toolCompare real underlays by TOG and check them against your carpet.Find low tog underlay underfloor heating on eBayaffiliateRelated
Sources: Interfloor (Duralay/Tredaire) · Ball & Young · Underfloor Heating Manufacturers Association (UHMA)