The words of underfloor heating, without the jargon.

The floor

Screed

A layer of mortar poured on the slab to obtain a flat floor, on which the floor covering is laid. A poured screed has to dry before it is covered. Water-based underfloor heating embeds its pipes in it; the system we fit does without: see fitting without screed.

Dry screed

Boards laid dry and joined together, which do the work of a screed with no water and no drying. One goes under large-format tiles, solid or large-plank wood flooring, or a thin glued floor covering.

Decoupling mat

A thin layer laid between tiles, or glued-down wood flooring, and the base beneath them. It absorbs the movements of one relative to the other when the temperature changes, and prevents cracks. See under tiles.

Levelling compound

A compound poured in a thin layer to make up for the defects of a floor before anything is laid on it.

Flatness

The gap allowed between the floor and a straight edge laid on it. For this system, the manufacturer requires 2 mm at most over one metre; beyond that, a levelling compound is needed.

Floating installation

Wood flooring, vinyl or laminate whose planks lock into one another, without being glued or nailed to the subfloor. It is the thinnest way of laying over underfloor heating.

Height added

Everything that is added to the existing floor, floor covering included. It decides what happens to the doors and thresholds: from 13 mm under click vinyl to 45 mm under solid wood flooring on dry screed, according to the manufacturer.

The system

Heating film

A thin sheet that heats when current passes through it. On a striped film, only stripes of carbon heat; on a full-surface film, the whole sheet. See the four families of carbon heating film.

Reflective layer

The bottom layer, 1 mm: it sends the heat back towards the room instead of letting it go into the floor, and it is vapour-tight.

Insulating and sound-deadening layer

The middle layer, 4 mm: it separates the film from the cold floor and deadens footstep noise.

Radiation

The way a warm surface heats what faces it, without going through the air. That is how underfloor heating heats; a convector heats air first.

Room thermostat

It measures the temperature of the room, switches the heating on below the set temperature and off above it. There is one per room: see the thermostat.

Hysteresis

The temperature gap between the moment the thermostat switches on and the moment it switches off. Half a degree for the manufacturer’s thermostat.

Floor sensor

A sensor placed in the floor, which limits its temperature. The manufacturer of the system does not provide for one; it remains possible, as a limiter, if the manufacturer of the floor covering asks for one.

Electricity and energy

Output and consumption

Output, in watts per square metre, says what the heating can deliver at a given moment: 115 W/m² here, 180 W/m² in a tiled bathroom. Consumption, in kilowatt-hours per square metre per year, says what it actually used over a year. Multiplying one by hours does not give the other: see measured consumption.

Direct electric heating

Heating that turns electricity into heat, with nothing in between: one kilowatt-hour paid for, one kilowatt-hour of heat. Electric radiators and electric underfloor heating are examples.

Heat pump

A machine that takes heat from outside, from the air or from the ground, and brings it into the house. It gives more heat than it consumes in electricity.

Seasonal performance factor

The number of kilowatt-hours of heat a heat pump gives for one kilowatt-hour of electricity, measured over a year. The Fraunhofer institutes recorded on average between 2.2 and 3.1 for air-source heat pumps, depending on the study and on what is counted: see heat pump or carbon underfloor heating.

Simultaneity

Not all the rooms heat at the same moment. For the consumer unit and the supply connection, the manufacturer allows 40% of the installed power.

Final energy, primary energy

Final energy is what the meter records. Primary energy adds what it took to produce it and deliver it. In France, one kilowatt-hour of electricity counts as 1.9 kilowatt-hours of primary energy in the energy certificate, 1.7 from 1 January 2027, and 2.3 in the regulations for new buildings.

Energy certificate

In France, the document that rates a home from A to G (diagnostic de performance énergétique). It is a calculation, not a reading of bills. Belgium, Luxembourg and the Netherlands each have their own, under another name.

The checks

Type examination

An independent body tests a sample of the product against a standard, and issues a certificate for that model. It covers safety, not consumption: see warranty and certifications.

CE marking

The manufacturer’s declaration that its product complies with the European rules that apply to it. For an electrical appliance, it is first of all the “Low Voltage” Directive.

Thermal camera

It turns the temperature of a surface into an image. At the end of the job, it shows that the whole floor heats: see the thermal camera check.

Is a word missing? Ask for it.

Updated on 9 October 2026.