Underfloor Heating Under Carpet: UK Guide
You can install underfloor heating under carpet, but carpet insulates the heat by design, so efficiency drops and running costs go up compared with a hard floor.
UFH works under carpet if the total tog rating (carpet plus underlay combined) is under 2.5, ideally lower for electric systems. Use a thin, UFH-rated underlay and loop-pile carpet. Heating efficiency drops 30-50% compared with tile, and running costs rise accordingly. It's workable in bedrooms where comfort matters more than efficiency, but it's not the best pairing if minimising running cost is the priority.
Tog rating explained
Tog measures thermal resistance, in other words how much a material insulates against heat passing through it. The higher the tog value, the more it insulates, and the less heat from your UFH system actually reaches the room above rather than being trapped in the floor buildup.
UFH manufacturers generally recommend a maximum combined tog of 2.5 for the carpet and underlay together. Electric UFH, which has less thermal mass and a lower power output per m² than most wet systems, is more sensitive to this and often has a tighter recommended limit, sometimes as low as 1.5 tog, so always check the specific manufacturer's guidance for the system you're installing.
Typical tog values for reference:
- Tile or stone: 0 tog (no meaningful insulation)
- LVT: around 0.1 tog
- Engineered wood: around 0.15 tog
- Thin, low-pile carpet: 1.0-1.5 tog
- Thick, deep-pile carpet: 2.0-2.5 tog
- Standard carpet underlay: 1.0-1.5 tog
- Thick or foam underlay: 2.0-3.0 tog
Add the carpet and underlay figures together to get your total. A thick carpet on a standard underlay can easily exceed 3.0 tog combined, well above the recommended ceiling, so the pairing matters as much as either product on its own.
Choosing carpet and underlay for UFH
If you're set on carpet over UFH, a few choices make a real difference to how well the system performs:
- Loop-pile carpet generally has a lower tog than cut-pile or deep saxony styles of similar thickness, because the fibre construction traps less air
- Thin carpet, under roughly 1.5 tog on its own, leaves more headroom for the underlay
- Rubber-backed carpet sometimes eliminates the need for a separate underlay altogether, simplifying the tog calculation to one product
- UFH-specific underlay, usually a dense rubber crumb or firm felt under 1.0 tog, is designed specifically for this pairing rather than for cushioning underfoot comfort, which is the priority for most standard underlay
Always check the manufacturer's published tog rating rather than guessing from feel; a carpet that feels thin can still carry a surprisingly high tog value depending on its fibre density.
Electric vs wet UFH under carpet
The two system types cope differently with a carpeted floor. Electric UFH has a relatively low power output, typically 150W per m², and a fast but shallow heat cycle. Carpet's insulating effect hits it harder proportionally, because there's less spare capacity to push through the extra resistance.
Wet UFH carries more thermal mass in the screed or dry board system beneath the floor. It responds more slowly to begin with, taking a few hours to warm up rather than the 30-60 minutes typical of electric UFH, but that mass also means it's somewhat less sensitive to a moderate tog carpet on top, since the system is already designed around gradual, steady heat output rather than quick bursts.
In both cases, installing carpet over UFH increases the time it takes for the room to reach temperature and increases the running cost for the same result, it's a question of degree rather than one system being immune to the effect.
Installation and safety notes
Fit and commission the underfloor heating system first, following the manufacturer's instructions for testing (electric cable resistance testing before and after any screed or levelling compound goes down), then fit the carpet and underlay on top once the floor is confirmed working and, for wet systems, the screed has fully cured.
With electric cable systems specifically, avoid underlay types that could be punctured or that trap moisture against the cables, and never nail, tack or staple carpet grippers through the heated area; fix gripper rods only around the room's perimeter, outside the cable or pipe layout, and check the system layout plan before doing so. Using an incorrect underlay or damaging cables during fitting is a common cause of warranty claims being refused.
Efficiency loss and running cost
Carpet under UFH reduces heating efficiency by roughly 30-50% compared with a hard floor covering like tile. In practical terms, a room that costs around £200 a year to heat with tile on top of wet UFH could cost £300-400 a year with carpet, for the same room temperature, because the system has to run longer and work harder to push heat through the extra insulation. See our underfloor heating running cost guide for the wider cost comparison between electric and wet systems.
When carpet over UFH makes sense, and when it doesn't
Carpet over UFH is a reasonable choice in bedrooms, where the priority is a warm, soft floor to step onto rather than minimising running costs, and where the room typically isn't heated to the same temperature as a bathroom or kitchen. It's a poor pairing in bathrooms (where carpet is unsuitable regardless of heating) and in any large open-plan area where running costs matter, since the efficiency loss compounds over a bigger floor area.
Alternative: LVT or engineered wood
If you want a softer, warmer-feeling floor with UFH but don't want the efficiency hit of carpet, LVT is a strong middle ground: it feels noticeably warmer and softer underfoot than tile, transfers heat well at around 0.1 tog, and is available in a huge range of wood and stone-effect finishes. Engineered wood is a similar compromise for a natural-material look. See our LVT flooring guide and engineered wood flooring guide for details.