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Underfloor heating is becoming more and more commonplace in our homes. They heat the floor with water heating, laying pipes in a screed, or electricity – various heating elements that turn electricity into heat. It is far from always possible to make a water heated floor – in old apartments it is unrealistic to get permission for it. It is easier with electric heating – you can find an option even for old floors, which gives the minimum load. But in order for the house to be warm, it is imperative to pre-calculate the electric floor heating. Then the cost of the arrangement will be optimal, and the power is sufficient even for the coldest periods.
Calculation methods
First of all, you need to decide whether you will have a warm floor as the main heating (without radiators and other heat sources) or additional (to increase comfort). Depending on this, the calculation of the electric floor heating changes. If floor heating is only additional heating, the only requirement is that there should be enough power to heat the floor to a comfortable 28,5-29°C. There are no other requirements. In this scenario, boldly use the average numbers, which are determined empirically (in the table below). When using floor heating as the main heating, the approach is different: there must be enough heat to compensate for heat loss. Here everything is somewhat more complicated – calculations are needed.
Calculation of electric underfloor heating by heat loss
There are two ways to make an electric floor heating calculation. The first one is just a calculation. When using this technique, the heat loss of the room is first determined. This takes into account the region in which the building is located, the material and thickness of the walls, the thickness and type of insulation, the size of the windows and the type of glazing, the presence and area of the walls facing the street, the orientation of the room (south, north, etc.). All these factors affect the amount of heat that leaves the room and that will have to be replenished.
Heat loss for each type of building material can be found in the special literature, there are separate methods. Such a calculation is a chore, but it allows you to get accurate data. This is in case you want to count yourself. If not, you can order a heat engineering calculation from specialists. And, if the areas for floor heating are planned to be large, it is better to order anyway. Sometimes, independently determined heat losses are several times higher than those that will be given to you by specialists. And extra power is a waste of money.
The resulting figure will be the power of the electric underfloor heating, which is necessary to compensate for the heat loss of this room. The whole calculation of an electric underfloor heating is to select the heating elements in such a quantity and such power that they give out the required amount of heat in total (it is possible with a small margin). If these are heating cables, it will be necessary to develop a laying scheme so that all the required cable footage is placed on a given area. If you decide to use a film underfloor heating, you need to look for a film of the required power. In any case, keep in mind that in order not to feel cold and hot places of heating with your feet, the distance between adjacent heating elements should not be more than 30 cm. And for normal heat redistribution (not in stripes), the minimum height of the screed should be – 3 cm, better about 5 cm.
Pay attention! Electric underfloor heating is laid only on the area that is not occupied by furniture and large household appliances. This is due to the fact that for the most part the heating elements of the warm floor do not tolerate overheating (except for the self-regulating heating cable). Therefore, the calculation of an electric underfloor heating begins with the location of furniture and appliances on the plan (on a scale). Having determined the area not occupied by the situation, you can proceed to the calculation. Another important point: if a warm floor is the main source of heat, then the heated surface should not be less than 70% of the total area of uXNUMXbuXNUMXbthe room.
Determining the required power depending on the purpose of the room
The second way is to count according to the average data. The amount of materials used in the construction of residential buildings is limited. This made it possible to derive the average figures for the required underfloor heating capacities for heating premises for various purposes. (see table).
| Type of heating | name of the property | Power required |
|---|---|---|
| Additional heating | Kitchen, living rooms on the ground floor | 140-150 W/m2 |
| Additional heating | Kitchen, living rooms on the second floor and above | 120-130 W/m2 |
| Additional heating | Bathroom | 140-150 W/m2 |
| Additional heating | Balcony, loggia | 180 W / m2 |
| Main heating | All premises, regardless of assignments | 180 W / m2 |
When calculating an electric underfloor heating, the unoccupied area found is multiplied by the rate taken from the table. They get a figure that an electric underfloor heating can give out. In principle, this will also be the maximum power consumption required for underfloor heating.
For example, if 10 square meters are heated in a living room on the ground floor, then the heating element can produce / consume 140 W / m2 * 10 m2 = 1400 W. This is the power consumption per hour. Don’t be afraid. In reality, such a flow can be only immediately after switching on and until the floor reaches the set temperature. During this period of time, the heaters operate continuously. Then the heating is turned on/off by the thermostat, which maintains the set temperature with an accuracy of 1°C. The amount of electricity consumed during this period depends on the weather (the colder, the more often it will turn on) and the degree of insulation of the floor and the room as a whole.
What can affect heat transfer
How well the floor heating will work is influenced not only by the power of the heating elements, but also by how well the whole “pie” is designed and made, how the materials are correctly selected.
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First of all, the heat transfer is affected by the coating, which is laid on top of the heating elements. For example, if a resistive or self-regulating cable, mats from it or a rod infrared floor are used for heating, most often they are poured into the screed. In this case, special mixtures for underfloor heating are used. Another option is to add additives to a standard cement-sand mortar that increase the thermal conductivity of concrete. The second option is cheaper, but you will have to look for information about the necessary additives. But you can save.
Then ceramic tiles are laid on the screed – in the bathroom, corridor, in the kitchen. In living rooms, laminate, linoleum, and carpet are more often used.
No matter what kind of flooring you plan to purchase, you should only use materials that are designed for laying on underfloor heating. They have increased thermal conductivity, normally tolerate prolonged heating. So the increased price is justified, and the heating will be more efficient.
The most unfortunate choice of finishing coating for underfloor heating is carpet. Even a special one, it conducts heat worse than all others. In order to heat it up to an acceptable 28-29°C, it is necessary to raise the temperature of the heating elements by 4-5°C more than with other types of finishes.
The most successful choice is ceramic tile or porcelain stoneware. They have good thermal conductivity, but they also have a high heat capacity – a lot of time passes until they warm up. It is necessary to lay tiles and a warm floor on a special glue.
When using heating cables (any) or underfloor heating, the laying technology is the same. First, the screed is poured, the concrete gains strength over 28 days, then the tiles are laid. When using heating cable mats, the process changes, and significantly: the tiles can be laid directly on top of the mats on the required adhesive layer. The consumption of glue in this case is large (the minimum layer of tiles + glue is 3 cm), but much less time is required.
Film underfloor heating can be done without a screed. It is placed under the laminate. Only a special substrate (for underfloor heating) is spread over the film and laminate can be laid. Under the linoleum or the same carpet, they make a rigid base – they put sheets of plywood, chipboard or OSB (OSB), and the finish coating is already laid on them. Such an electric underfloor heating device – without a screed – is possible only if there is radiator heating. Everything fits quickly, but the heating is inefficient – high heat transfer cannot be achieved by any means.
Thermal insulation
The better the insulation of the floor under the electric heaters, the less electricity will be required to maintain a normal temperature. If during construction the floor was already sufficiently insulated, it is possible not to lay the insulation. Although any system – you lay a cable or film floor – indicates the need to use a heat-insulating substrate. They are different in different systems, but their presence is desirable. Then, making the calculation of the electric underfloor heating according to average statistics, you can take the required power along the lower edge or even a little lower. And this is money saved both during installation and during operation (less heat is spent on non-target heating).
A little about the heat-insulating materials that are recommended for use when installing a warm floor. The most optimal is extruded polystyrene foam (EPS). It has sufficient density and strength to withstand the pressure of the screed and everything that will be on it. The second option is high-density sprayed thermal insulation. The method is even better, but also more expensive. The density under the screed requires a high 60-80 kg / cubic meter, and such sprayed thermal insulation costs even more than XPS. True, it has the best characteristics for today (thermal conductivity is almost the same as that of air 0,2-0,3, depending on the manufacturer).
Often, when laying an electric underfloor heating, it is advised to use thermal insulation with a foil surface. This is argued by the fact that the foil reflects heat rays into the room. It works like this, but with an air gap between the heater and the foil (at least 3 cm). There are no and cannot be any air gaps in the pie of the warm floor. So laying this material is just a waste of money and time. There is another argument against laying a layer of foil under a warm floor. The foil in the concrete crumbles to dust after a few weeks and becomes completely useless. They cannot even redistribute heat more evenly in this state.
Temperature controllers and sensors
The electric floor heating circuit assumes the presence of a thermostat and a temperature sensor. Their presence is not necessary – you can manually turn the heaters on and off. But only together with these devices, the system will work normally, for a long time, provide the required level of comfort, rationally use electricity, and avoid overheating. The presence or absence of a temperature controller with a sensor does not affect the calculation of an electric underfloor heating, but it affects the service life very much. As already mentioned, the vast majority of heating elements are afraid of overheating, and it is very difficult to avoid it with manual control. A couple of times you don’t have time to turn it off in time, the cables / film / mats will melt.