Rugs and underfloor heating – what works, what melts

By Emma Whitfield · Published 22 September 2026 · 7 min read

Underfloor heating (UFH) is now the default in new UK builds and about a third of retrofits. The wrong rug over it does two things: it wastes 30–60% of the heat you paid for, and it can trip the safety cut-out on electric mats. Here is the short list of what to check.

The single number that matters: 2.5 tog

The Underfloor Heating Manufacturers Association (UFHMA) publishes a combined ceiling of 2.5 tog for the rug plus underlay together. Above that, water-based systems lose enough output that the flow temperature has to be pushed up – burning more gas or electricity to compensate – and electric systems risk overheating.

Most machine-made polypropylene shaggy: 1.5–2.5 tog. Safe.
Hand-tufted wool, 12 mm pile: 2.0–2.8 tog. Borderline. Skip the underlay.
Hand-knotted wool, 20 mm+ pile: 3.5–4.5 tog. Too high – heat cannot pass.
Flatweave kilim, cotton or wool, under 5 mm: 0.5–1.2 tog. Ideal.
Jute or sisal, natural weave: 1.0–1.8 tog. Safe on tog, but jute yellows at sustained 27 °C floor temperature.

Backings that trap heat

Latex, foam and PVC backings are common on budget rugs – and none of them belong over UFH. They trap heat, yellow the flooring below and, on electric systems, are explicitly disallowed by Warmup, ThermoSphere and Nu-Heat installer guides. What to look for: natural cotton backing, woven jute backing, or UFH-approved written on the label.

Materials that work

Wool flatweaves and kilims – best of both worlds. Wool tolerates 27 °C floor temperature (BS EN 1307) and flat construction stays under the tog cap.
Cotton flatweaves – safe, washable, cheap. Fades faster under sun over UFH than a wool equivalent.
Polypropylene under 10 mm pile – cheap, safe, no shed. Feels less premium.
Kilim – the traditionally correct answer. Reversible, thin, wool.

Materials to avoid

Viscose (art silk) – sheds badly and mats when warm-damp air rises through it.
High-pile shaggy (25 mm+) – every manufacturer warns against it.
Any rug with a rubber, foam or PVC backing.
Jute – fine on tog, but discolours at sustained warm-floor temperature.

Frequently asked questions

Is 2.5 tog really the ceiling?

It is the industry rule of thumb from the Underfloor Heating Manufacturers Association (UFHMA) – above 2.5 tog, the system loses more than 30% of its output through insulation, and the water flow temperature has to compensate. Below 2.5 tog covers most machine-made rugs; hand-knotted wool and shaggy over 20 mm pile push above it.

Can I run underfloor heating hotter to compensate?

Not by much. Most water-based UFH systems are capped at 55 °C flow (BS EN 1264), and the floor surface must stay under 27 °C – a limit set for comfort, not the equipment. Adding a thick rug means the exposed floor around it heats to the cap while the rugged area lags.

What about electric UFH under a rug?

Electric UFH manufacturers explicitly warn against high-tog rugs – the heat cannot escape upward, the mat overheats, and the safety cut-out trips. Warmup, ThermoSphere and Nu-Heat all publish this in their installer guides. Rug up to 2.0 tog only.

Our verdict

Buy flatweave wool or kilim, skip the underlay, check the label for a tog figure (or ask the seller for one – Amazon.co.uk listings under-declare this). If in doubt: pull the rug back for a week and see if the room feels warmer. If it does, you were over the cap.

Sources

Underfloor Heating Manufacturers Association (UFHMA), Floor coverings compatibility guidelines, 2024.
BS EN 1264 – Water based surface embedded heating and cooling systems.
Warmup plc installer manual, 2025 revision.