How to Install Electric Underfloor Heating Under Tiles

This guide walks you through installing the EkoBuild AHT amorphous metal ribbon system under tiles. The ribbon is 1.8mm thin, delivers 150W per square metre, and needs no screed or self-leveller of its own. It has gone into more than 100 UK homes and carries a 15-year warranty, honoured directly by the UK importer.

One thing before we start. Planning and laying the mats is genuinely DIY-friendly. The final electrical connection is not. A qualified electrician must make that connection under Part P of the Building Regulations and BS 7671. Everything else in this guide, you can do yourself.

Tools and materials checklist

• AHT ribbon heating mats, 0.5m wide (£45 per m2) or 1m wide (£65 per m2)
• Therm-All insulation, £53.50 per 10m2 pack
• WiFi touchscreen thermostat, £89.99
• Flexible tile adhesive rated for underfloor heating (any tile shop or builders' merchant)
• Tiles, flexible grout and spacers
• Tape measure, pencil and paper for the layout
• Scissors or a sharp knife for cutting insulation
• Notched trowel for the adhesive
• Vacuum and brush for subfloor prep
• A qualified electrician booked for the final connection and thermostat

Planning and measuring your room

Start with a sketch. Mark the bath, toilet, shower tray, basin and any fixed units. You heat the open floor you walk on, never under fixtures, so measure that area rather than the whole room.

The ribbon comes in two widths. 0.5m wide mats are £45 per square metre in lengths from 1m to 7m. 1m wide mats are £65 per square metre in lengths up to 3.5m. Narrow bathroom layouts usually suit the 0.5m width. Bigger open floors, like a kitchen, often take the 1m mats with fewer runs.

If the floor will be the room's main heat source, cover at least 70% of it. That is the minimum for running the system as primary heating, and the primary heating guide explains it in full. In a bathroom with a heated towel rail, or a kitchen with a radiator, the floor is topping up other heat and coverage matters less.

Two shortcuts. For a straightforward bathroom, the Bathroom Complete Kit at £299 takes the guesswork out. And for any room, the room designer lets you draw the room, then plots the exact ribbon layout and prices it on the spot.

What you need

Nothing on the list is hard to find. The heating parts come from the EkoBuild shop, with free UK delivery on orders over £150 and £9.99 delivery under that. The tiling materials come from any tile shop or builders' merchant. The full kit list is below. The short version: mats, insulation, thermostat, flexible adhesive, and an electrician booked in for the final connection.

Step-by-step: installing the ribbon under tiles

None of the stages are difficult, but do them in order and give each one the time it needs.

1. Measure and plan the layout. Measure the open floor, keeping clear of the bath, toilet and any fixed units. The room designer turns your measurements into an exact ribbon layout and price.
2. Prepare the subfloor. The floor needs to be clean, dry, solid and level. Screw down loose boards, then vacuum thoroughly. A single piece of grit under a mat can cause damage once the tiles go down.
3. Lay the insulation. Cut Therm-All insulation to cover the heated area with the joints butted tight. Insulation drives the heat up into your tiles instead of down into the subfloor, so the room warms faster and costs less to run.
4. Roll out the ribbon mats. Lay the mats to your plan. Never cut or shorten the heating element itself, never overlap mats, and keep them clear of fixtures. At 1.8mm thin, the ribbon barely changes your floor height.
5. Fit the floor sensor. Underfloor heating thermostats read the floor temperature through a small sensor probe. Position the sensor between two ribbon runs, following the instructions supplied, with the cable routed back to where the thermostat will sit.
6. Cover the mats with flexible tile adhesive. First, check every mat for damage and have your electrician test them. Once tiled, a fault is expensive to reach. Then trowel a full, even bed of flexible tile adhesive over the mats. The ribbon needs no screed. The adhesive bed is simply how tiles are fixed, and flexible adhesive is standard trade practice over any heated floor. Go gently with the trowel so you do not nick the element.
7. Tile and grout. Bed the tiles fully into the adhesive with no voids underneath. Air pockets above a heated floor create hot spots. Grout once the adhesive has set, following the manufacturer's timings.
8. Get the electrics connected. A qualified electrician makes the final connection and fits the WiFi touchscreen thermostat. This part is covered by Part P of the Building Regulations and BS 7671. Laying the mats is DIY-friendly. The electrics are not.
9. Let the adhesive cure before first heat. Do not switch on until the adhesive and grout have fully cured. Follow the adhesive manufacturer's guidance on timing, then bring the floor up to temperature gradually rather than running it at full heat straight away.

Tiling over the ribbon: what to know

Ceramic, porcelain and natural stone all work well over electric underfloor heating. Tile conducts heat and holds it, which is why bathrooms and wet rooms are such popular places for electric underfloor heating, with kitchens not far behind.

Three points of general tiling guidance worth following:

• Use flexible adhesive and grout. A heated floor expands and contracts slightly as it warms and cools. Adhesive rated for underfloor heating copes with that movement. Rigid adhesive can crack. Ask at the tile counter for a flexible adhesive suitable for heated floors and they will point you at the right bag.
• Large tiles want a flat base. Big-format tiles show up every dip in a floor. If your subfloor is uneven, a thin self-levelling layer over the mats gives you a flat surface to tile on. The ribbon itself does not need it. That is purely a tiling decision.
• Wet rooms need tanking as normal. If you are waterproofing a wet room, follow your tanking membrane manufacturer's guidance on the order of layers. The heating does not change your waterproofing responsibilities.

Tiles are one option among several. The same ribbon lays directly under carpet, wood, laminate and vinyl too. The no-screed guide covers how each floor type goes down.

Common mistakes to avoid

• Cutting the heating element to fit. Never cut or shorten the element. Plan properly instead. With 0.5m mats available in lengths from 1m to 7m, there is a combination for almost any room shape.
• Heating under the bath or toilet. Fixed fixtures trap heat over the mat. Keep the ribbon to open floor you actually walk on.
• Skipping the insulation. Without it, a chunk of your heat disappears into the subfloor. The room is slower to warm and dearer to run. Leaving it out is a false economy.
• Dabbing adhesive instead of a full bed. Dot-and-dab leaves air pockets under the tiles, and air pockets over a heated floor become hot spots. Full, even coverage every time.
• Tiling without testing. Have the mats tested before the adhesive goes on. Finding a fault under fresh tiles is a miserable, expensive job.
• Using the heating to dry the adhesive. Tempting, and a known way to weaken the bond. Let the adhesive cure at room temperature for the full time the manufacturer states.
• Doing your own final connection. The electrical connection must be made by a qualified electrician under Part P and BS 7671. No exceptions.

What it costs: a real bathroom example

Take a typical family bathroom of 5m2, with about 3.5m2 of open floor once you take out the bath, toilet and basin.

• 0.5m ribbon mats, 3.5m2 at £45 per m2: £157.50
• One pack of Therm-All insulation (covers up to 10m2): £53.50
• WiFi touchscreen thermostat: £89.99

Total: £300.99, with free UK delivery because the order is over £150. Add your tiles and adhesive, which you are buying anyway if you are retiling, plus your electrician's connection charge. That varies by area, so get a local quote.

Prefer one box with the heating side sorted? The Bathroom Complete Kit is £299.

A kitchen runs the same maths at a larger size. Six square metres of heated floor comes to £270 in 0.5m mats, plus the same thermostat and insulation pack: £413.49 all in.

Next steps

The fastest way to plan your room is the room designer. Draw the room, mark the fixtures, and it gives you an exact ribbon layout with a price.

Browse the mats, thermostat and insulation in the shop, or read the full electric underfloor heating guide if you are still comparing systems. Got an awkward room and want to talk it through? Call us on 07883 298944. The system has gone into more than 100 UK homes, so there is a fair chance we have already seen a room like yours.

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