Before laying, a thermal calculation of the room is made, heat losses are determined, and then, based on the value obtained, a cable of the required power is selected. On average, in standard high-rise buildings without insulation, heat loss is 100 W / sq.m. The cable is selected so that excessive heating of the floor is not allowed, the surface temperature of which should not exceed 30–35 C.
The cable is laid in a screed on a prepared (ideally even) surface. A layer of heat-reflecting material is laid under the screed, for example, a lavsan film with a metallized coating. The heat-reflecting layer does not allow the heat to “leave” down, but not every material is suitable for such a layer, so it is better to check with the manufacturers which material they recommend.
The screed is usually made from a cement-sand mixture (wet cement screed), but a dry screed has recently become widespread (for example, from expanded clay backfill). The thickness of the screed layer above the cable is usually made no more than 4–5 cm. Too thin screed will be fragile, and too thick will be excessively massive. It will slowly heat up and cool down just as slowly, and this is inconvenient (recall that the main advantage of electric heating is a very quick access to the calculated heating temperature, a thick screed nullifies this advantage).
Make a preliminary cable layout diagram. The cable should be evenly placed on the floor, the distance between the individual cable strands (laying step) should not exceed the value specified by the manufacturer (usually about 20 cm). Too large a laying step leads to the fact that the screed warms up unevenly. The cable is attached to the base using plastic or metal clamps. You can also purchase a ready-made option — a warm floor based on a mat with a heating cable, in which the cable is already fixed on the basis of their plastic mat. Such ready-made kits are much easier to lay, since you do not have to make sure that the laying step is too large or small, or, say, the bending radius of the cable is too small. The advantage of a cable over a mat is greater flexibility and variability in laying.
Try to determine in advance where furniture with low legs (or no legs at all) will be placed — cabinets, beds, etc. The areas of the floor occupied by such furniture will be isolated from the heat exchange between the cement screed and the air in the room. It makes no sense to lay a cable in them.
The heating cable can be resistive and self-regulating. A resistive cable heats up evenly along its entire length, regardless of the ambient temperature, and a self-regulating cable is able to respond to this temperature and reduce or increase the intensity of heat generation. If a segment of such a cable heats up, then the intensity of its heat release decreases, and vice versa. This is very convenient, since such a self-regulating cable will not overheat if it finds itself in conditions of insufficient heat exchange, if, for example, a cabinet is placed on the floor where it is located or a carpet is laid. Therefore, if you do not know exactly how the furniture will be arranged and the carpets will be laid out, be sure to choose a self-regulating cable for installation.
Do not forget about floor temperature sensors that register the degree of heating of the cement screed and give a command to turn the heating on and off. They should be placed in the screed at the maximum distance from the heating cable threads, exactly in the middle between them.
In the process of laying a wet cement screed, it is not allowed to turn on the cable for heating. If you turn on the warm floor until all mortars (cement screed or tile adhesive) have completely hardened, then the drying mass will crack.