For uniform heating of the room air, convector heaters can be replaced by a floor heating system. Problems arise only where large window areas are involved, but this can be overcome by the installation of additional heating-such as floor convectors.
In general, surface heating includes large areas of surface surrounding a room and involves relatively low temperatures. Types of surface heating include floor heating, ceiling heating and wall heating. With floor heating, the heat from the floor surface is not only imparted to the room air, but also to the walls and ceiling. Heat transfer to the air occurs by convection, i.e. by air movement over the floor surface. The heat given to the walls and ceiling takes place due to radiation. The heat output can vary between 70 and 110W/m^2, depending on the floor finish and system employed. Almost any usual type of floor finish can be used – ceramics, wood or textiles. However, the diathermic resistance should not exceed 0.15m^2k/W.
House dust allergies can be a problem in heated rooms. Previously, precautions against house dust or dust mite allergy paid no attention to the effects of heating units. Heaters cause swirling of house dust containing allergens, which can then rapidly come into contact with the mucous membranes. In addition to this, there are insoluble difficulties in cleaning heaters which have convection fins. It is therefore advantageous if heaters are designed to embody the smallest possible number of convection elements and to have straightforward cleaning procedures. These requirements are fulfilled by single-layer panes without convection fins and by radiators of unit construction.
**Storage of heating oil** : The quantity of heating oil stores should be sufficient for a minimum of 3 months and a maximum of one heating period. A rough estimate of the annual requirement for heating fuel is 6-10/m^3 of room volume to be heated. A maximum volume of 5m^3 may be stores in a boiler house. The container must b within a storage tank capable of accepting the total quantity. Storage containers in the ground must be protected from leakage, e.g. through the use of double-walled tans, or plastic inner shells. Maximum capacities and additional safety measures are prescribed for areas where water protection regulations are in force. Within buildings, either plastic battery tanks with a capacity per tank of 500-2000 litres may be installed, or steel tans which are welded together in situ, whose capacities may be freely chose. The tank room must be accessible.
The tanks must be inspected for oil-tightness are regular intervals. In the event of an emergency, the tank room must be able to retain the full amount of oil. Tank facilities must have filling and ventilation pipe lines. Additionally, overfilling prevention must be incorporated and depending on the type of storage, a leak warning system may be prescribed (e.g. in the case of underground tanks).
The floor screed for floor heating systems must satisfy local regulations. The thickness of the screed depends on the type of covering used, its preparation and the anticipated loading. A minimum covering over the heating pipes of 45mm is prescribed when using cement floor screed and heating pipes which are directly above the thermal insulation. If there is no fininish over the basic floor, then a minimum total depth of 75mm is required. The floor screed expands during use, and a temperature difference arises between the top and bottom surfaces of the screed.
Due to the differential expansion, tensile stresses occur in the upper region of the layer. In the case of ceramic floor coverings, this can only be countered by top reinforcement. On carpeted floors or parquet floors the reinforcement can be avoided, since the temperature drop between the upper and lower surfaces of the floor covering is less than in the case of a ceramic finish. Special requirements are contained in the thermal insulation regulations with respect to the limitation of heat transfer from surface heating, irrespective of the choice of type of insulation method: In surface heating, the heat transfer coefficient of the component layer between the hot surface and the external air, the ground, or building section having an essentially lower internal temperature, must not exceed a value of 0.45W/m^2.
The maximum permissible floor surface temperature for a permanently occupied area is 29^c. For the boundary zone it is 35^c, where the boundary zone is not to be wider than 1m. For bathrooms, the maximum permissible floor temperature is 9^c above normal room temperature.
Under normal conditions, floor heating is possible, since the heating requirement seldom lies above 90W/m^2. In only a few exceptions (e.g. when there are large window areas, or when the room has more than two external walls) is there a greater heating requirement, and then additional static heating surfaces or air heating must be installed in additions to the floor heating.