A correct determination of the necessary power must be based on a calculation, for example according to the ČSN EN 12830 regulation (Thermal systems in buildings - Calculation of heating performance). The main issue here is the general concept and construction of the building, particularly the materials and technologies used in construction. In general though, it can be said, that in a building which meets the contemporary energy requirements, so it is a building with a "B" energy label (51 – 97 kWh/(m2.year)), the value of necessary power for floor heating somewhere around 70 W/m2 in normally tenanted rooms such as bedrooms, kitchens aso. This value corresponds to a maximum 27°C surface temperature of the floor, a 20°C calculation temperature in the room and a minimal outdoor temperature of -15°C.
In bathrooms, swimming pools and saunas, is the performance of floor heating for a 29°C maximum floor temperature and a room temperature of 24°C, somewhere around 85 W/m2. For a better dynamic of the system, it is possible to raise the performances when installing the floor sensors, up to 100 W/m2 in residential rooms and up to 160 W/m2 in rooms of the bathroom type. From an increase like this we obtain a power reserve for periods with lower outdoor temperatures or an eventual need to raise the room temperature. Furthermore, it speeds up the floor temperature startup in sudden weather changes or when a higher room temperature is required.
