How to install an electric underfloor heating mat

An electric mat is the quickest underfloor heating to fit: a heating cable fixed to a self-adhesive mesh about 3 to 4mm thick, laid in the tile adhesive bed. This guide covers the order of work for a tiled floor, the tests that protect your warranty, and the mistakes that are expensive to fix once the tiles are down. If you have not chosen between a mat and loose cable yet, read our guide to electric loose cable vs mats first.

What size electric underfloor heating mat do I need?

You need a mat that matches the free floor area, which is the floor left after you take out anything fixed. Choose the mat size closest to that figure without going over it, because the heating cable can never be cut to shorten the mat.

1. Measure the room and work out the total area.
2. Take off the area under baths, shower trays, kitchen units, islands and the toilet.
3. Choose the mat output: 100W/m² for low heat loss rooms, 150W/m² for most kitchens and bathrooms, 200W/m² for conservatories and rooms that lose more heat.
4. Pick the mat size at or just below the free area.
5. Check the load: watts divided by 230 gives amps. Keep the total within the thermostat's 16A rating, which is about 3.68kW at 230V.

Worked example. A 2.4m x 2.7m bathroom is 6.48m². The bath (1.7 x 0.7m) takes 1.19m², and the toilet and pedestal about 0.6m². That leaves about 4.7m² of free floor. The closest mat without going over is 4.0m². At 150W/m² that is 600W, which draws 600 ÷ 230 = 2.6A.

What do I need before I start?

You need the mat, a floor-sensing thermostat, a primer, and the right base for your subfloor. Gather everything first so you can lay and tile in one go.

• Thermostat: a floor-sensing thermostat that switches up to 16A, such as the Heatmiser neoStat-e (app control with a neoHub) or Slimline-E (no app). Both come with a floor sensor.
• Primer: to seal dusty or porous floors so the mat mesh and adhesive bond.
• Insulation board: cement-coated XPS board under the mat cuts heat lost downwards, so the floor warms faster. It comes in 6, 10 and 20mm.
• Uncoupling membrane: on timber, new screed or mixed subfloors, to stop movement cracking the tiles and grout.
• Tools: a multimeter, a camera (your phone), scissors for the mesh, and flexible tile adhesive.

How do I test an electric underfloor heating mat?

You test the mat with a multimeter before you lay it, after laying it, during tiling and once the floor is finished. Each test takes a minute and proves the cable has not been damaged before it is buried.

Write each reading down with the date. Never test a mat by connecting it to the mains. If a reading changes between tests, stop and find the cause before you carry on tiling, because a damaged cable can't be repaired once it is under tiles.

How do I prepare the floor for an electric mat?

You prepare the floor by making it clean, flat, dry and sound, then priming it. The mat sits in a thin adhesive bed, so any high spot or loose material will show through the tiles.

1. Lift old coverings and remove adhesive, paint and dust.
2. Check the floor is flat. Fill hollows with a levelling compound and let it dry.
3. On timber floorboards, overboard first to give a rigid, even base, then use an uncoupling membrane.
4. Fit insulation boards if you are using them. Bond XPS boards in flexible tile adhesive and fix them with insulation board washers.
5. Prime the surface and let it dry to the primer maker's time.
6. Mark the fixed items on the floor in pencil so you keep the mat out of them.

Where should the floor probe go?

The floor probe goes in a conduit, halfway between two runs of heating cable, reaching about 400mm into the heated area. Set it before the mat goes down, so it never crosses the cable.

• Chase a shallow channel so the conduit sits level with the top of the cable.
• Seal the end of the conduit so adhesive can't get in. That way you can pull out and replace the probe later without lifting a tile.
• Keep it away from hot water pipes, and from places a rug or furniture will cover, or it will read the wrong temperature.
• Run the conduit up the wall to the thermostat back box with the cold tail.

The floor probe also protects the floor finish from overheating.

How do I lay an electric underfloor heating mat?

You lay the mat from the thermostat end, rolling it out across the room, cutting only the mesh at each wall and turning the mat back on itself. The heating cable stays in one piece the whole time.

1. Place the cold tail so its 3m lead reaches the thermostat position. Keep the joint between the cold tail and the heating cable flat on the floor. It must be buried in the adhesive, never bent or left in the wall.
2. Roll out the first 0.5m wide strip, mesh side down, to the far wall.
3. At the wall, cut the mesh (not the cable) and turn the mat to run back alongside the first strip.
4. Keep going until the free area is covered. If a gap is too narrow or awkward for a 0.5m strip, leave it unheated, or use loose cable for that room instead.
5. Check no cable touches or crosses another, and none runs under a fixed item.
6. Press the mat down firmly once you are happy with the layout.
7. Test the mat again, then photograph the whole floor and draw a plan with the cold tail and probe positions. Keep both with the thermostat instructions.

How do I tile over an electric heating mat?

You tile over the mat in flexible tile adhesive, fully covering the cable with no air pockets. Air gaps leave hot spots on the cable and weak spots under the tiles.

1. Spread a layer of flexible adhesive over the mat with the flat side of the trowel, working it through the mesh to cover the cable.
2. Comb a second layer with a notched trowel and bed the tiles as usual. Take care not to drag the trowel teeth across the cable.
3. Test the mat again part way through tiling and after the last tile is laid.
4. Grout once the adhesive has set.

Our mats are made for tile and stone floors. If you want wood, laminate, vinyl or carpet, the build-up is different, so check the floor maker's guidance before you buy.

Who can connect electric underfloor heating?

A qualified electrician must make the final connection, with the circuit protected by a 30mA RCD and installed to BS 7671. In England, the work is notifiable under Part P if it needs a new circuit, or if it adds to or alters a circuit in the space around a bath or shower.

A registered competent person electrician can self-certify the work. Otherwise, building control must be told before work starts. The mat's cold tail and the floor probe connect straight to the neoStat-e or Slimline-E, which switch up to 16A without a separate contactor. For thermostat choice and larger loads, read electric UFH thermostats and 16A loads. Bathrooms have extra rules on zones, covered in electric underfloor heating in bathrooms.

When can I turn on electric underfloor heating after tiling?

Wait until the tile adhesive and grout are completely dry, which is normally at least 7 days, or longer if the adhesive maker says so. Don't use the heating to dry the adhesive faster, as that can crack the bond.

When you first switch on, set a low temperature and raise it gradually over the first days. Set the thermostat's floor limit to suit the floor finish, so the floor never runs hotter than the tile or stone maker allows.

Products for this job

Prices below include VAT, October 2026. Kit for the 6.48m² bathroom in the worked example:

That is £338 before tile adhesive and the electrician. Ten boards cover 7.2m², which allows for cuts. For a thermostat without an app, the Heatmiser Slimline-E is £56. On timber or new screed, add the uncoupling membrane (1m x 5m, £57). Higher and lower outputs: the 200W/m² mat and the 100W/m² mat. A spare 10K floor probe is £13.

Browse the full range: electric mats and electric thermostats.

Frequently asked questions

Can I install an electric underfloor heating mat myself?

You can lay the mat and tile over it yourself. The final connection must be made by a qualified electrician, on a 30mA RCD, to BS 7671, and the work may need to be notified under Part P.

Can you cut an electric underfloor heating mat?

You can cut the mesh to turn the mat or fit it round obstacles. Never cut, shorten or join the heating cable. If the mat is too big, it was the wrong size: choose one at or below the free floor area.

Can I put an electric mat under a bath or kitchen units?

No. Keep the mat out of any area that will be covered by a bath, shower tray, units, an island or the toilet. Heat trapped under fixed items can overheat the cable.

Do I need insulation boards under an electric mat?

They aren't compulsory, but on a concrete floor much of the heat goes downwards without them. A 6 or 10mm XPS board under the mat makes the floor warm up faster and costs less to run.

How long does it take to install an electric underfloor heating mat?

Laying a mat in a typical bathroom takes a few hours, plus the primer drying time. Tiling follows the same day or the next. Allow at least 7 days after tiling before you switch it on.

Can the cold tail joint go in the wall?

No. The joint between the heating cable and the cold tail must lie flat in the floor, fully bedded in adhesive. Only the cold tail itself runs up the wall to the thermostat.

What if a test reading changes after tiling?

Stop and get an electrician to check it before the floor is finished. A cable damaged during tiling can't be repaired under the tiles, which is why you test before, during and after.

Sources: Approved Document P (gov.uk), IET Wiring Matters: BS 7671 Section 753 floor heating, Heat Mat heating cable installation instructions, Danfoss DEVImat 150T data sheet