Bathrooms and other wet room
The bathroom is the room in the house with the longest tradition of electric underfloor heating. There are multiple reasons why electric underfloor heating is the preferred choice here, among which the heating of the room, freeing up of space and the requirement for a safe and secure installation, both with respect to handling and the risk of electrical shock, are the most important. Since tiles, which is the most common top flooring in bathrooms, feel cold when they have a temperature of 22-23°C (normal room temperature), heating cables in bathroom floors are normally used year round, so as to keep a comfortable floor temperature of 27-28°C.
It is rarely necessary to perform a heat loss calculation for dimensioning heating cables in a bathroom floor. In houses built according to modern standards, the installed power should be in the range 120W/sqm - 150W/sqm. Consideration must be made with respect to heat obstacles and top flooring when the electric underfloor heating system is dimensioned.
Heat Obstacles are objects in and on the floor, near, or under, which heating cables must not be installed. Examples of these are integrated bath tub, cabinet with a base (not feet), drains and piping in the floor. If much floor area is lost on account of heat obstacles, it may be necessary, or desirable, to increase the installed power in the remaining, available area, so as to ensure sufficient heating of the whole room.
Traditional / conventional screed thickness in a floor is about 5 cm. Nexans normally recommends a maximum thickness of 6 cm, as going beyond this gives an extremely thick floors with a high degree of thermal storage (meaning slow adjustment of temperature). The lower part/layer of concrete/screed in thicker floors can also be quite challenging to compact when being poured, which in turn can lead to reduced thermal conductivity. This may, consequently, mean even further reduction of the possibility to adjust the temperature of the floor. In worst case, a layer of concrete with insufficient thermal conductivity may result in overheating of the heating cable and ultimately damage to and malfunction of the cable.
In bathrooms, tile is the most common floor covering, but coverings made from PVC or other plastic materials are also widely used. When using tiles, Nexans recommends a maximum installed power of 150W/sqm. 160W/sqm is an absolute limit of what is approved, and an installed power higher than this will void the warranty of the heating cable. Using PVC flooring, or similar, Nexans recommends installing maximum 100W/sqm, but this is in the interests of the flooring and the possibility of discoloration of this. If a supplier of such flooring approves higher installed power, then the same limitations as when using tiles apply. Note, however, that it a thicker layer of screeds is required when using PVC flooring as compared to using tiles.
Temperature control and adjustment
In order to achieve the most energy efficient floor, is recommended to use an electronic, programmable thermostat, which allows for day and night setback. The degree of efficiency will depend largely on the installed power and the thickness of the floor (in combination with the quality of the screed used).
In wet room, a waterproof membrane shall be installed in the floor, so as to prevent water from flowing through the concrete and into the framework of the building (or even further). This membrane can be mounted on the floor base, before the screed is poured (the "bottom membrane"), or it can be installed on top of the concrete floor ("top membrane). Both types of membrane are approved by Nexans for use with our heating cables. Note though, that in a floor with a bottom membrane, the heating cable will lie in a very moist environment with high pH (alkaline environment) throughout its lifetime, something which represents an additional challenge for the heating cable.