Helpful video reference. We use Rayotec's installation guide "Tips to Install Foil Electric Underfloor Heating for Under Carpet, Laminate and Engineered Wood" as the video reference here. Rayotec Ltd is a family-run UK underfloor heating company based in Sunbury-on-Thames, Middlesex, with over three decades of experience in the sector. Their guide is practical, product-accurate, and UK-specific.
1. Plan the mat layout
Measure the room and draw a rough plan showing where fixed furniture will sit permanently. Foil underfloor heating must not go under fixed items such as wardrobes, beds with solid bases, or kitchen units because the heat cannot escape and the mat will overheat. You are heating the usable floor area, not the footprint of the whole room.
From the net heated area, calculate the wattage. Most foil mats are rated at 100 to 150 W/m². For a typical bedroom or living room used as supplementary heating, 100 W/m² is usually sufficient. Decide where the thermostat will sit on the wall: it needs to be close enough to the floor zone for the sensor cable to reach without splicing.
2. Prepare the subfloor
The subfloor must be clean, flat, and completely dry before anything goes down. Sweep and vacuum thoroughly. Check for high spots with a long straight edge and fill any hollows deeper than 3 mm with self-levelling compound, leaving it to cure fully before proceeding.
Any damp or moisture issue in the subfloor must be resolved first. Foil and moisture are a poor combination, and trapping damp under a sealed floor layer will cause the mat and the boards above it to fail prematurely.
3. Lay the thermal insulation boards
Lay the insulation boards tightly across the entire floor area, including under furniture. Without a thermal break beneath the mat, a significant proportion of the heat travels down into the subfloor rather than upward through the floor covering. Polyiso (PIR) boards at 6 mm thickness are commonly used; some systems specify XPS foam boards.
Tape every joint with foil tape to create a continuous thermal break and to stop the boards shifting when you walk across them. Any gaps between boards will create cold lines in the finished floor.
4. Roll out and cut the foil heating mat
Starting from the thermostat wall, roll the foil mat out across the heated zone. When you need to change direction, cut straight across the mat between heating elements along the pre-printed cut lines. Never cut through a heating element itself. The cut lines are clearly marked on most mats, but check the manufacturer's instructions before making any cut.
Leave the gap specified by the manufacturer between the mat edge and the skirting board (typically 50 to 100 mm) and keep the mat away from the entire footprint of any fixed furniture. Do not overlap sections of mat.
5. Secure and tape the mat
Fix the mat firmly to the insulation boards using foil tape along all edges, across any cut lines, and along both sides of every join. The mat must lie flat so the floor covering above it is not affected by ridges or lifted edges.
Route the mat's power cable toward the thermostat position in a straight line, keeping it flat against the insulation board surface. Where the cable crosses a joint between insulation boards, tape it securely on both sides so it cannot shift during floor laying. Many installers run the cable in a shallow channel pressed into the insulation board to keep the floor perfectly flat at that point.
6. Install the thermostat and floor sensor
Mount the thermostat backplate on the wall at the height specified by the manufacturer (commonly between 150 mm and 1.5 m from the floor). Run the floor sensor probe cable from the backplate, under the door threshold or through a conduit groove if necessary, to a position between two heating elements in the middle of the heated zone. The sensor tip should sit between elements, not on top of one, for accurate temperature reading.
Many installers run the sensor cable inside a thin conduit or tape it in a groove cut into the insulation board surface. This means the sensor can be replaced in the future without lifting the floor covering.
7. Wire the thermostat to the mains supply
With the circuit isolated at the consumer unit and confirmed dead with a voltage tester, connect the incoming supply conductors to the thermostat's mains input terminals: live to live, neutral to neutral, and earth to earth. Then connect the mat's tail cable to the thermostat's load terminals following the same convention.
Most programmable thermostats are double-pole switching, meaning both live and neutral are broken when the thermostat is off. Follow the wiring diagram in the thermostat's instructions precisely. Fit the thermostat faceplate, ensuring no conductors are trapped behind the backplate.
If you are not confident wiring the thermostat, or if the installation requires a new circuit from the consumer unit, this is the point to call a qualified electrician. The thermostat wiring is the part of the job that carries real risk if done incorrectly.
8. Test resistance before laying the floor covering
Before any floor covering goes down permanently, measure the mat's resistance with a multimeter across the two supply conductors. The manufacturer's data card supplied with the mat will give you the expected resistance value and the acceptable tolerance range.
A reading significantly outside the stated range (typically more than 10% above or below) indicates a damaged element, almost certainly caused by a cut through a heating wire during installation. A damaged mat must be replaced or repaired before the floor goes down. Laminate and engineered wood are difficult to lift cleanly once they are fixed, so this test is not optional.
9. Lay the floor covering and commission the thermostat
Lay the laminate, carpet, or engineered wood as you normally would. For laminate, leave the expansion gap around the perimeter as the manufacturer requires. For carpet, confirm the carpet and underlay combined tog rating is within the mat manufacturer's specification (usually 2.5 tog or less).
Once the floor is down, restore the power and commission the thermostat. Set the floor temperature limit first: for laminate and engineered wood this is typically 27°C; exceeding this can cause boards to warp or joints to open over time. If the thermostat is programmable, set the schedule to suit the room's use pattern. Run the system for 30 minutes and confirm that the floor feels warm across the heated zone and that the thermostat is reading and responding correctly.
When to call us
The mat laying steps are well within DIY reach, but wiring the thermostat safely and compliantly is a different matter, particularly if a new dedicated circuit is needed. Richard can wire the thermostat, certify the electrical installation, and advise on the right circuit arrangement for your property.
Need the wiring sorted for underfloor heating?
Richard can supply and wire the thermostat, run a new spur or dedicated circuit if required, and provide the completion certificate for Part P compliance.
Contact Richard