Underfloor heating is only as good as the floor covering above it. Choose the wrong build-up and you will pay to heat the underside of your own flooring. This guide covers what to fit, what to avoid, and the commissioning steps that prevent gaps, cupping and warranty problems.
Wet versus electric systems
Wet (hydronic) systems circulate warm water through pipes buried in screed or laid in joist trays. They run at low flow temperatures, typically 35–45°C, heat up slowly and hold their heat. They are common in extensions and new builds across Kent and are the more efficient long-term option.
Electric systems use a mat or loose cable under the floor finish. They respond quickly, are much cheaper to retrofit, and are the usual choice for bathrooms and kitchens in existing houses. They can produce hotter localised surface temperatures, which makes floor-covering choice more critical.
Either way, the governing number is surface temperature. Almost every flooring manufacturer sets a maximum of 27°C at the floor surface. Exceed it and you invalidate the warranty and risk shrinkage gaps in wood and adhesive failure in vinyl.
Total tog: the number that decides efficiency
Heat has to pass through everything you put on top of the pipes: underlay, the floor covering, and anything else in between. The industry rule of thumb is that the combined tog value of the underlay plus the floor covering should not exceed 2.5 tog, and lower is better.
That single rule eliminates a lot of products. A thick 11mm PU carpet underlay alone can be 2.0 tog before the carpet is even down. A heavy wool twist on top pushes the total well past 3.0 tog, at which point the system will struggle to warm the room at all.
Where carpet is non-negotiable, use a low-tog underlay specifically marketed as underfloor-heating-compatible, and choose a short-pile carpet with a hessian rather than felt back. Realistically you can achieve about 2.0–2.3 tog total, which works but is not the system's best performance.
- LVT glued down: ~0.1–0.3 tog — the best-performing choice
- Engineered wood, glued: ~0.6–1.0 tog depending on thickness
- Laminate with UFH-rated underlay: ~1.0–1.5 tog
- Carpet with low-tog underlay: ~1.8–2.4 tog — workable but inefficient
- Solid hardwood: not recommended, and often not permitted by warranty
The best options in practice
Glue-down LVT is the outright winner. It is thin, conducts heat quickly, is dimensionally stable, and being fully bonded there is no air gap to insulate. Response times are fast and there is nothing to lift or cup. For kitchens, bathrooms and open-plan ground floors with UFH, this is what we fit most often.
Engineered wood is the best option if you want real timber. Choose a board no thicker than 15mm, glue it down fully, and make sure the manufacturer explicitly approves it for underfloor heating. Wider boards are more prone to visible seasonal gapping over UFH, so 150–180mm widths are the safer bet.
Laminate works with a compatible underlay but tends to feel cooler than the numbers suggest, because a floating floor traps a thin insulating air layer. It is the budget option rather than the performance option.
Commissioning: the step most people skip
Every new screed must be fully cured before the heating is turned on — usually a minimum of 21 days for sand-cement screed, and the manufacturer's figure for liquid screeds. Firing up early traps moisture and will destroy an adhesive bond.
Once cured, the system must be commissioned before the floor goes down: run it at low temperature and raise it in 5°C increments daily to maximum, hold for several days, then bring it back down to about 18°C. This drives out residual moisture and expands the screed before your floor is bonded to it.
Keep the system at that low temperature during fitting and for at least 48 hours afterwards, then raise it gradually again. Rushing this sequence is the single most common cause of gapped wood floors and lifting vinyl over UFH.
Practical rules for a retrofit
Retrofitting into an existing room usually means an electric mat over the existing subfloor, a levelling compound over the mat, then the finish. Build-up height matters: allow 15–25mm and check it against your door thresholds and kitchen plinths before ordering anything.
Always specify a floor sensor, not just an air thermostat. The floor sensor is what enforces the 27°C limit and protects your floor covering; an air stat alone can allow surface temperatures to overshoot badly on a cold morning.
Finally, use flexible adhesive rated for underfloor heating. Standard adhesive goes brittle through repeated heating cycles and eventually lets go — usually at the doorway, where the failure is most visible.
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Frequently asked questions
What is the best flooring for underfloor heating?
Glue-down LVT. It is thin, thermally conductive, stable and fully bonded, so heat reaches the room quickly with no insulating air gap. Engineered wood glued down is the best real-timber alternative.
Can you put carpet over underfloor heating?
Yes, but only with a low-tog underlay and a short-pile carpet, keeping the combined total under 2.5 tog. Expect slower response and higher running costs than a hard floor.
What temperature limit applies to floor coverings?
27°C at the floor surface is the standard maximum for almost all manufacturers. A floor sensor wired to the thermostat is the only reliable way to enforce it.
Do I need to commission underfloor heating before fitting?
Yes. Cure the screed fully, then cycle the system up to maximum and back down before the floor covering is laid, and keep it low for 48 hours after fitting. Skipping this causes gapping and adhesive failure.