Underfloor heating under tiles, LVT, laminate, engineered wood and carpet

The finish is the last layer between the heat and the room, and it is the one most often chosen without checking. A thick underlay or the wrong board can take a well designed system and make it feel weak. A floor that runs too warm can open gaps in wood or lift vinyl.

This guide gives the numbers for each finish and how to set the controls to protect it. The finish affects the design, so pick it before the pipe centres are set.

How does the floor covering affect underfloor heating?

The floor covering acts like a layer of insulation on top of the heating. The higher its thermal resistance, the less heat reaches the room at the same water temperature, so you need warmer water or closer pipe centres to make up for it.

One UFH system maker's output table for a 65mm sand and cement screed, 150mm pipe centres and a 45/35°C flow and return shows the effect:

So in that table, 15mm wood gives about 30% less heat than tile, and carpet about 41% less. With a heat pump, where you want the lowest flow temperature, this matters more. See will underfloor heating heat my room? for how to check output against heat loss.

What is a tog value and what are typical figures?

Tog is a measure of thermal resistance used for carpets and underlays. 1 tog equals 0.1m²K/W, so 2.5 tog is 0.25m²K/W. Add the tog of every layer above the heating to get the total.

These are the CIBSE figures published by one UFH maker. For your own floor, use the figure on the flooring or underlay maker's data sheet.

How hot can the floor surface get?

For comfort, BS EN 1264 limits floor surface temperature to 29°C in occupied areas, 35°C in edge zones such as along cold outside walls, and about 33°C in bathrooms, as summarised by one heating maker. Many floor finishes have a lower limit of their own.

Always check the limit for the exact product you buy. The flooring warranty usually depends on it.

Are tiles and stone the best floor for underfloor heating?

Yes. Ceramic, porcelain and stone tiles have almost no thermal resistance, so they pass the most heat at the lowest water temperature. They also suit electric mats, which sit in the tile adhesive bed.

• Use a flexible tile adhesive suitable for heated floors.
• On timber or new screed, an uncoupling membrane helps stop subfloor movement cracking the tiles and grout. Ours is fleece-backed and bedded in flexible adhesive.
• Over a calcium sulphate screed, sand off the laitance and prime before tiling. See screed depths and drying times.
• For electric heating under tiles, our mats are made for tile and stone floors and come in 100, 150 and 200W/m².

Can I have LVT or vinyl over underfloor heating?

Yes. Most LVT and vinyl is approved for UFH, with a limit of 27°C. One vinyl maker measures that limit at the underside of the flooring, at the adhesive line, and says the floor finish industry agrees on 27°C as the maximum.

1. Commission the heating and dry the screed fully before the floor goes down.
2. Switch the heating off 48 hours before installation, as one vinyl maker's guidance requires.
3. Lay the vinyl and keep the heating off for at least 48 hours after.
4. Bring the heating back slowly. For adhesive-free flooring, the same maker raises it 5°C a day.

Vinyl conducts heat well, but some makers advise against it in high heat loss rooms such as older conservatories, where the floor would need to run hot.

Can I put laminate on underfloor heating?

Yes, most laminate is suitable. One laminate maker allows a contact temperature of up to 27°C and a total thermal resistance of no more than 0.15m²K/W, laminate and underlay together. It must be laid floating.

• Choose an underlay sold for UFH, with a low tog. A thick acoustic or insulating underlay can push you over the limit.
• Thinner, denser boards pass heat better than thick ones.
• Tell your installer the floor is laminate so the system is set to keep within 27°C.

Can I use engineered wood with underfloor heating?

Yes. Engineered wood is usually a better choice than solid wood over UFH because its layered core is more stable as the temperature changes. One wood flooring maker limits the surface to 27°C.

• Choose thinner, denser boards. 13mm hardwood is about 1.0 tog.
• The screed must be dry first. One wood flooring maker sets a maximum of 1.8% moisture for cement screed.
• The same maker keeps air humidity between 40% and 65% during acclimatisation, and raises the heating 1 to 2°C a day once the floor is laid.
• On joisted floors, see underfloor heating in joisted timber floors for board thickness limits over spreader plates.

Can I have carpet over underfloor heating?

Yes, if the carpet and underlay together are 2.5 tog or less. A UK carpet maker gives the same combined limit, and so does UFH maker guidance. Lower is better: every tog you save lets the system run cooler.

Worked example. A medium pile carpet of 1.5 tog on an 8mm underlay of 1.0 tog totals 2.5 tog. That is at the limit. Swap to a 5mm underlay of 0.5 tog and the total drops to 2.0 tog, which gives more heat at the same flow temperature.

• Avoid thick rubber crumb or felt underlays marketed for warmth. Check the tog on the label.
• Carpet slows warm-up, so start heating schedules earlier in carpeted rooms.

How do I protect the floor from overheating?

Use a floor probe so the thermostat can read the floor temperature and cap it below the flooring maker's limit. On wood, laminate and vinyl this is the simplest way to stay within 27°C.

1. Fit a 10K floor probe in a conduit between the pipe runs or heating cables, not on top of them, so it can be replaced later.
2. Connect it to a thermostat with floor sensing. The Heatmiser neoStat V3 accepts 10K, 12K and 15K NTC probes. The neoStat-e for electric floors comes with a floor sensor.
3. Set the floor limit to the flooring maker's maximum, or a degree or two below it.
4. Set the water flow temperature at the blending valve or heat source so the floor can't overheat even at full demand.

Our guide to floor probes and air sensing explains the settings in more detail.

Products for this job

• 10K Floor Probe for UFH Thermostats (3m)
• Heatmiser neoStat V3 Smart Thermostat
• Heatmiser neoStat-e for electric floors
• Uncoupling Membrane (1m wide roll)
• Pipe Conduit for 16mm Pipe
• Electric underfloor heating mats
• Insulation and tile backer boards

Frequently asked questions

What is the best flooring for underfloor heating?

Tile and stone, because they have almost no thermal resistance and pass the most heat. LVT and thin engineered wood are next. Carpet works but gives the least heat.

What tog should underlay be for underfloor heating?

Keep the carpet and underlay together at 2.5 tog or less. Pick the lowest tog underlay you can, often 0.5 to 1.0 tog.

Can you put a rug on underfloor heating?

Yes, but a thick rug acts like extra insulation and the floor beneath it gets warmer. Check that the rug and floor finish together stay within the flooring maker's limits.

Does solid wood work with underfloor heating?

Some solid wood is approved, but it moves more than engineered wood as temperature and humidity change. Use it only where the wood maker approves it for UFH, with a floor probe limit.

Can I lay flooring straight after the screed heat-up?

No. The heat-up proves the system works, but the screed must also pass a moisture test for your floor finish. Vinyl also needs the heating off 48 hours before laying.

Why does my underfloor heating feel weak with carpet?

Carpet and underlay resist heat flow. In one maker's table, 1.5 tog of carpet cuts output by about 41% compared with tile. Check the total tog and consider a thinner underlay.

Can electric underfloor heating go under wood or carpet?

Our electric mats are made for tile and stone floors, sitting in the tile adhesive. For other finishes, check with us before you order.

Sources: Uponor floor coverings guide (CIBSE resistances), Danfoss UFH design guide (EN 1264), Timoleon staple system data sheet, Altro flooring and UFH installation guide, Quick-Step laminate and UFH, Solid Wood Flooring Company UFH advice, Cormar Carpets UFH advice, Energy Saving Trust