Cable (wired) floor heating can be of two types: resistive and self-regulating cables. Resistive constantly emit the same amount of heat. Self-regulating ones change their thermal power depending on their own temperature: the more they heat up, the less heat they emit. They are also called "smart cables".
A warm floor from a heating cable requires the most insignificant costs for the purchase of the cables themselves. But they make it necessarily under the screed. This requires a mortar with fine grains and high-quality cement. You can use ready-made mixtures specifically for underfloor heating. In this case, the heat transfer will be higher, which means that the heating of the room is more efficient. But the components for the screed also require money. So, when considering the cost of this type of "electric floor", you need to include these components. And since the cable floor requires the thickest screed (5-6 cm) and fastening (mesh or fastening tapes), then the monetary “weight” of this component will be decent. Add significant labor intensity of the process and a long production time (at least 4 weeks due to the fact that the screed dries for 28 days). So the price of a heating cable is far from the entire cost of a warm floor.
Cable underfloor heating in the general case looks like this
Resistive heating cables
Resistive heating cables are available in single and twin cores. They are connected to the network through special couplings. The principle of their operation, regardless of the number of cores, remains the same: when a current passes, thermal energy is released. Only the connection method changes. In single-core cables, current flows through one conductor. In order for the circuit to be closed, both ends of the bay must be connected to the power supply.
How to connect single-core and two-core heating cables
In practice, laying is done as follows: they fix the transition sleeve at the connection point (without connecting near the thermostat), roll out and lay the cable so that the second “cold” end (this is the cable that is located after the sleeve) is in the mounting box. After connecting both couplings, the circuit is closed and the cable is ready for operation. Please note that the couplings remain on the floor and then fall into the screed, and only "cold" wires are brought to the walls.
Connecting a two-core resistive cable is simpler: only one end is connected, the second has a plug. In order for the circuit to be closed, it has a second current-carrying core.
The structure of both types of heating cables is similar: one or two cores in insulation, a metal braid that protects against damage and gives a greater degree of rigidity, everything is covered from above with a layer of outer insulation. Some brands may have drainage veins that serve to reduce the intensity of electromagnetic fields.
The structure of a two-core heating cable for underfloor heating
If we talk about the cost, then the two-core ones are a little more expensive. But they are still popular. Firstly, because it is easier to lay them (there is no need to put the other end on the thermostat), and secondly, because they create electromagnetic fields of lower intensity (the movement of electrons is multidirectional and the fields partially compensate each other).
For all that, both options have a significant drawback: they emit a constant amount of heat. If heat is not removed for some reason, the cable will overheat, which can lead to its failure. Therefore, when using resistive wires, they are not laid under furniture and make sure that voids do not form in the screed. Air has low thermal conductivity, and in the area where there is a bubble, heat is removed at an insufficient rate, which leads to an increase in the temperature of the cores and their failure.
Self-regulating heating cables
These heating wires will not overheat, due to their specific structure. A self-regulating cable is a serial connection of a huge number of small heating elements. Each of them consists of two conductive wires, between which there is a polymer. This polymer generates heat. This is not a cable in the usual sense, but a matrix made in the form of a wire / cable.
The structure of a self-regulating floor heating cable
The self-regulation of such an electric field is based on the property of the polymer: its electrical resistance strongly depends on temperature. The higher the temperature, the greater the resistance. Therefore, as the polymer heats up and its resistance increases, the current passing through the element decreases, and the amount of heat generated decreases accordingly. In this way, he can regulate the amount of heat that each segment gives off. Moreover, the temperature indicators of neighboring elements do not depend on each other.
The property is remarkable, but the cost of such a cable floor will be much higher: the price of self-regulating conductors is several times more expensive than resistive ones, and the laying method is the same.
Cable underfloor heating device
Any of the heating wires, if damaged, loses its performance. Therefore, cable underfloor heating is most often laid in a screed. Moreover, the thickness of the screed is chosen such that even large loads could not damage the wires inside. On the other hand, too thick a layer will greatly reduce the efficiency of the cable heating system and make it inertial. A very large layer can even cause the floor to not be warm even at maximum power. Therefore, choosing the thickness of the screed, based on the principle of reasonable sufficiency.
The electric floor heating circuit provides for the presence of a thermostat (thermostat) and a floor temperature sensor. You can, of course, do without them by directly connecting the cables to the power supply. But such a system will not work for a very long time: during operation it will give out the maximum temperature it is capable of, it will quickly overheat and fail. Especially if you use resistive cables. Therefore, when installing a cable underfloor heating system, we first install a thermostat.
The first thing you should do is check the resistance of the cable and its insulation. The resistance of the cores must match the passport (a passport with all technical data is attached to each coil of the cable: length / power / weight / resistance). If the data matched or differed by no more than 10%, you can continue editing.
Installing the thermostat
First you need to decide on the location of the thermostat. It is placed on one of the walls at a distance of at least 30 cm from the floor. Most often, thermostats are placed near the switches at eye level. A recess is cut out in the wall for a standard socket. You can put it both lower and higher, but you will need to somehow control the state of the system, and a thermostat located too low or high will be inconvenient.
The thermostat will increase the comfort of underfloor heating and save money
After a hole of the appropriate size has been made in the hay and a mounted box has been installed, power is supplied - zero, phase and ground (without connecting). Then a strobe is punched, directed from the thermostat to the floor. Three or two pieces of pipe or corrugated hose are placed in it. One / two segments come out of the wall near the floor - connecting wires from heating cables are placed in them. The pipe section or corrugated hose located between them must also pass along the floor and end at a distance of about 0.5-1 meter from the wall. The wires from the floor temperature sensor are laid in it. In this case, if the sensor fails (a fairly common failure), it can be easily replaced: remove the thermostat panel and pull out the damaged sensor by the wires from the corrugation or pipe, and then insert and connect the correct one.
Foundation preparation
Now about the device of the cable underfloor heating itself. The base is cleaned and leveled. If necessary, with a screed 3-7 cm thick. An even base is an important nuance. If you skip this step, the heating will be uneven, and if there is an air bubble under the resistive cable due to unevenness, it will quickly burn out.
Thermal insulation is laid on a flat, clean base to reduce heat loss. It consists of two parts: a tape, which is laid around the perimeter of the room and direct thermal insulation of the floor surface. When choosing thermal insulation, do not forget that it must be heat-resistant, i.e. tolerate temperatures up to 100°C.
The thickness of the thermal insulation layer depends on the level of heat loss through the floor. If you have an unheated basement below, you need to lay a thicker layer, if there is another apartment under you, then 2 cm of thickness can be dispensed with. In principle, you can not use a heat insulator at all, but then up to 30% of the power will go down.
It is better to take thermal insulation with a metallized layer, but not with foil
Insulation for cable underfloor heating is best taken with a metallized surface. So the heat, which under normal conditions is directed downward, will be reflected and heat not the interfloor overlap, but the screed located above. You can use ordinary heat-insulating material, and roll out a reflective film on top. Please note that it is useless to put foil in the screed - it collapses in a few months. So it's money thrown to the wind.
You can use both rolled heat insulators and plates. You can’t leave gaps between them, we adjust everything closely: any gap is a cold bridge through which heat escapes. The heat insulator is fixed depending on the subfloor: on double-sided tape, staples of the construction stapler, glue. The joints are sealed with tape. You can use the usual assembly, but better metallized. If the humidity in the room is high (bathroom, kitchen, toilet, etc.), a layer of waterproofing is laid on top of the thermal insulation. It can be a dense plastic film or other modern material.
Then there are two options: you can make a preliminary cement-sand screed of small thickness. It will contribute to a more even distribution of heat. This option prevents overheating of the cables. But you can do without this step. Then a grid with a cell of 1-1.5 cm or a special mounting tape (preferably) is laid on top of the waterproofing film. Tape laying step - 40-50cm. Nets are placed close to each other.
Mounting tape fasten cables faster
Read more about underfloor heating materials here.
Calculation of the power of cables for underfloor heating
The thermal power of an electric underfloor heating is calculated based on the nature of the heating. If the warm floor is an auxiliary heating system, it will take 110-140W to heat 1m2, if the system is the main (the only one), then they count 150W and more. It is clear that in many respects the amount of heat for heating depends on how much heat has gone into the floor. If you want to pay less for heating, make high-quality floor insulation.
Approximate norms of thermal power depending on the purpose of the premises (data for central Russia)
It is also necessary to determine the size of the area on which the cable will be laid out. It definitely does not need to be laid under furniture, plumbing or hanging low objects. This is necessary for resistive cables - they are afraid of overheating, for self-regulating cables this is not critical, but why heat furniture? By discarding these zones, you determine the actual heating area. Now you can calculate the total power of the electric floor heating: multiply the heating area by the norm for 1m2.
For example, an area of 11m2 will be heated in a room, a warm floor is auxiliary heating, but the thermal insulation of the floor is not very good, and the height of the ceilings does not allow laying a thick layer of heat insulator. Therefore, we take the maximum consumption: 140W. It turns out that we need 11m2 * 140W = 1540W for heating.
Underfloor heating option under the board without screed
For example, let the cable power be 16.5 W/m. Then 1540/16.5=93.3m. Choose several bays with a total length close to the estimated figure. Here's another thing to consider: if you have an extra piece of cable left, you can't cut it off. Couplings are attached to its ends using special equipment. It is possible to make something similar on your own, but the service life will not be 10-20 years, as manufacturers guarantee, but only a few years, but rather months, depending on diligence. Therefore, we lay the entire length.
Cable management
The power ends of the cables lead to the wall to the thermostat. Moreover, the couplings must remain in the screed. The heating elements are laid with a “snake” or “snail” (it is better to develop a scheme in advance). The "snail" is more difficult to implement, and does not provide benefits when using heating wires. Therefore, for cable underfloor heating, they almost always use “snake” laying. A double or triple "snake" can be used, or several loops can be sequentially laid. Read more about cabling schemes here.
Examples of the location of heating coils
The laying step is chosen based on the required thermal power: the closer the wires are, the greater the thermal power. The minimum distance between two adjacent conductors is 5cm, the maximum is 30cm. The specific distance is also chosen based on the purpose of the rooms: in children's and bedrooms, the step is usually smaller, in living rooms and common areas - less. You can also reduce the step in the door / window area, and reduce it in the middle of the room. The main thing, when developing a cable layout, remember that the wires should not touch and intersect, the distance from the walls to the cables is at least 15 cm.
After laying the heating cables, install the floor temperature sensor. The wires from it lead through a corrugated hose to the thermostat. It should be located between two wires, preferably in the middle. If the height of the screed is sufficient, you can lay the pipe with the sensor just on top and fix it. If the thickness of the solution is not enough, you will have to ditch the subfloor. To prevent the solution from getting inside the corrugation, you need to close the end with something, for example, with electrical tape or tape.
Finishing fill
Before pouring the screed, you need to check the performance of the cables. Brem tester and measure the resistance. It must match the passport data. The maximum allowable deviation is 10%. Be sure to check this parameter, otherwise you will have to break the screed and remove it later.
If everything is fine with the heating wires, you can fill the screed. If you did not lay the thermal insulation, but mounted it directly on the subfloor, then the thickness of the screed can be 3 cm. If there is thermal insulation, the concrete layer cannot be less than 6 cm. Only at this height of the cement layer will you ensure sufficient floor rigidity. You can make a screed layer less if you use a hard floor covering - laminate, parquet board, etc. How to choose a topcoat for underfloor heating, read here.
Assortment of one of the companies selling cables for underfloor heating
After leveling the layer of concrete mortar, leave everything for 3-4 weeks. Only after this period can the heating cables be connected to the thermostat. There are clamps on it, to which you first connect the heating cables, and then to the corresponding ones - the power wires. If working with electricity is not your forte, it is better to entrust this procedure to an electrician. That's all. Cable underfloor heating is ready. It remains to lay the flooring. But here, too, there are nuances.
What types of flooring can be used with cable underfloor heating
Where can this type of underfloor heating be used? Resistive cables feel good under tiles, slightly worse, but are quite compatible with laminate, wood floors or linoleum. If you can take any tile, then laminate and linoleum need special ones without a layer of insulation. Today, in the characteristics of these floor coverings, there is often a characteristic: "suitable for underfloor heating." Underfloor heating made of resistive wire must not be covered with carpets or laid under furniture. But self-regulating can be used everywhere, and these zones too.
If you are laying tiles, the adhesive and grout should be special for underfloor heating: they have greater elasticity and better thermal conductivity.
Results
It takes a lot of time to make cable underfloor heating. Most of it goes to the "setting" of the concrete mortar screed. Another minus is the rather large thickness of the cake of materials: at least 5-6 cm. The pluses include the low cost of a linear meter of cable, but the cost of making a screed, insulation, fastening tapes, etc. must also be added to the total cost. As a result, the cost is much higher. Therefore, before making a decision, it is worth familiarizing yourself with other possibilities for arranging an electric underfloor heating. If you want to lay the cable floor under the tiles, then look at the materials on electric mats or film infrared floors. Take a closer look at carbon rod mats. They, like carbon films, emit heat in the infrared range. These materials get along well with ceramic tiles, and are easier to install. The cost of heating when comparing these options should be compared relative to a square meter, not a running one.
The advantages of film and rod heaters include the fact that they radiate heat in the infrared range. And this range is better perceived by the human body, since we also radiate heat in the same range. Therefore, when heated with infrared warm floors, the comfortable temperature is 2-3 ° C lower than with thermal radiation. This results in reduced energy costs. To the advantages of a rod IR floor, you can add its ability to self-regulate (IR films do not have such an ability), that is, it is not afraid of overheating and reduces its temperature in the right places. So, as always, the question "Which is better"? there is no clear answer.
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