Electric underfloor heating foil: checks before you lay it

The roll of electric underfloor heating foil is on the subfloor, and the decision comes before any board locks down. Leave the mat uncovered until the insulation is underneath it, the floor probe can be replaced, and the resistance matches the label in the box. This is the hour when a quilt underlay ends up on the wrong side of the mat, or the probe gets taped across a heating wire. Both are still easy to correct while the floor is open. Both become a lift once the skirting is back on.

The Products Compared editorial team wrote this page in October 2026 from UK installation guides: ThermoSphere's foil guide, Uheat's foil manual, the Protiler foil manual, and a foil manual hosted by Total Tiles. Those sheets disagree on millimetres, so the manual in your box wins where they differ. We have not lab-tested a mat, and this article does not quote an amazon.co.uk price, star rating, or review count. If you buy through our electric underfloor heating foil comparison, a qualifying purchase can earn us a commission at no extra cost to you.

In short

Use electric underfloor heating foil under a floating floor unless the manual in your box allows another finish. Put the insulation under the mat, and leave a floor probe conduit or a spare floor sensor so a failed probe does not mean lifting the floor. Match the resistance to the label before you cover the mat, keep the floor-temperature limit on, and let an electrician make the mains connection.

A floating floor, unless your manual says otherwise

These guides describe electric underfloor heating foil as floating floor heating under laminate or a similar floating finish. Tile and cement are a separate build-up. The foil manual hosted by Total Tiles says cement does not go on that foil system. If your manual describes a tiled finish, follow that page, including the board and the adhesive it names.

You can tile over heating foil only when the manual packed with your mat sets out that build-up. The four guides used here do not share one tile method, so keep a cable-mat method with the cable mat it was written for. If your sheet never mentions tile, ask the maker before you buy adhesive. A photo of a tiled room on a different product is a weak reason to bury this foil.

Read the cover section before you open the underlay, and set the mat out on the subfloor while the boxes are still closed, including the doorways and the run back to the thermostat. A wrong top layer stays until you lift the floor. Follow the sheet that names your model.

Put the insulation under the mat, never on top

Insulation belongs beneath the foil, so the heat has a path into the room. The Protiler foil manual puts the insulation under the mat and tells you not to put insulation on top of the mat. A layer above the foil holds heat in the build-up, and the room gets less of the output you bought the mat for. People reverse that ban when a spare roll of underlay is already in the hall.

An underfloor heating insulation board is the layer these manuals mean. A soft quilt sold for ordinary laminate is a different product. Buy the board your heating manual names, including any coating it specifies. This article will not give you a thickness in millimetres, because the guides do not agree on one depth.

Fit the boards before you roll the mat. Mark the thermostat wall, the cold-tail route, and the strip where the floor probe conduit has to travel. Boards that stop short of that route leave you cutting a channel after the foil is down, which is when the mat gets nicked. Leave any extra insulation off the top of the mat unless your manual names that layer.

Place the floor probe so you can replace it

The foil heating mat floor sensor tells the thermostat when the floor is warm enough. After the floating floor is down, that probe is out of reach unless you left a way back to it. ThermoSphere's foil guide treats a spare sensor or a conduit as part of the install, and it asks you to test before you cover the mat and again afterwards. A failed probe should be a pull-through or a swap at the thermostat.

Uheat's foil manual places the sensor about 25 cm into the heated area, between the cables. Protiler's manual asks for a conduit at least 50 cm from the wall. If your manual prints a different distance, use that distance. Sit the probe between the cables and keep it off the heating wire, then tape it so it cannot drift onto a wire while you lay the floor.

Run the floor probe conduit from the thermostat into the heated area before the mat is fixed, and cut it to the length your sheet shows. A conduit that stops under the skirting leaves you with no route when the sensor fails. A spare floor sensor is the other route ThermoSphere allows: a second probe laid now and left unconnected at the thermostat until you need it. Keep the floor-temperature limit enabled. ThermoSphere's guide prints a 27 degree floor limit, written as 27°C, and your thermostat should keep the limit your own manual prints.

Match the resistance to the label before you cover it

Test the mat before you cover it, and test it again once the floating floor is down and the room is still empty. ThermoSphere's installation guide asks for that before-and-after check. Compare the reading with the figure on your mat's label. There is no universal ohm value for electric underfloor heating foil, because a short run and a full-room mat will not measure the same. Match the reading to your label, inside the tolerance that maker prints.

Write the label value in the notes the manual gives you, then measure with the meter that sheet names. If the reading misses the match your manual allows, stop and leave the mat uncovered. A failed test before the floor goes down is an afternoon, and a failed test after the boards are locked means emptying the room. This page will not print a plus-or-minus band, because that band lives on the label for your size of mat.

Insulation resistance uses an instrument electricians carry, and these guides treat that test as the electrician's reading. A continuity beep on a basic multimeter does not complete it. If that meter is not yours to interpret, leave the reading with the electrician who connects the system, and write down the resistance you did take before anyone covers the foil. A match to the label still leaves the insulation side and the probe position as checks you make by eye.

Hand the mains connection to an electrician

Laying the mat and connecting it to the mains are different jobs. These guides put the thermostat supply with an electrician. UK mains are 230 V, and the electrician foil connection is the normal end of the install. The supply and the thermostat wiring belong with the person who will sign that work. This page stops at that handover.

Leave the heating wire at the length it left the factory. If the cold tail will not reach the back box, use the fix your manual allows: a thermostat closer to the mat, a deeper box, or the joint the sheet actually draws. Adding a homemade length of heating wire is how a mat that passed its first test fails the second one under a finished floor. Plan the thermostat wall when you plan the boards, while the mat is still a roll.

Foil is a different system from a wet underfloor loop. An underfloor heating actuator is the head on a valve for one water loop at the manifold, and it opens or closes that loop. The foil mat heats the floating floor under its own thermostat and floor probe. If one piped room is cold and the boiler is running, start with that valve head. If you are about to cover a thin electric mat, stay with the foil installation steps.