The device for floor heating of an apartment or a private house begins with calculations. Pipes or heating cables must be correctly selected according to the specific heat output and laid in a certain step. Practice shows: you cannot rely entirely on the experience of hired builders, it is better to develop a laying scheme yourself. How to calculate the electric and water floor heating by available methods is described in the further instructions.
We find out the required thermal power
To calculate all the parameters of the future warm floor - water or electric - you need to determine how many watts of heat to apply for heating a particular room. We suggest calculating the required heating power in the simplest way - by area or volume of the room.
Tip. Installation of floor heating circuits is not cheap. The price of work, taking into account materials and components, ranges from 5-8 y. e. per square meter (without installing and connecting the boiler). If you plan to hire a team of craftsmen and do not have a heating system project, require all the calculations from the performers to be completed, then compare the results.
As an example, we use the layout of a small one-story house of 100 m² (according to the external measurement), shown in the drawing. Note that corner rooms with light openings and external walls will lose much more heat in winter than internal rooms - a corridor, a bathroom and a hallway. The nuance is taken into account in the proposed methodology:
- By measuring and multiplying the lengths, find out the quadrature of each room.
- The areas of rooms with one outer wall and a light opening multiply by 0.1 kW. This category also includes the central premises (in the example - an entrance hall, a bathtub and a corridor).
- To heat rooms located in the corners of the building, you will need to allocate more thermal energy. The square of the room with two external walls and a window should be multiplied by 0.12 kW (kitchen and children).
- If there are 2 or more window openings in the corner room, the area is multiplied by 0.13 kW (living room and bedroom are on the layout).
The calculation results are the required heat dissipation of heating circuits or radiators in kilowatts separately for each room. With the received numbers, you can proceed to the next stage of the calculation.
Note. The indicated values are valid for the middle zone of the Russian Federation and the Republic of Belarus. For dwellings located in the south, the values of thermal power must be multiplied by a factor of 0.7. In the northern regions, an upward factor of 1.5–2 is applied to the results.
The above technique is not suitable for rooms with ceilings of 3 meters or more. In such cases, the required amount of heat is calculated by the volume of the premises, multiplied by 35, 40 or 45 W, depending on the location inside the building. The calculation of the load on the heating system is described in detail in a separate article.
Calculation of water heating circuits
Having found out what power of the heat flux is required to produce a warm floor in each room, calculate its main parameters in the following order:
- Determine the flow rate of the coolant that provides the necessary heat transfer to the circuits. Find out and adjust the surface temperature of the floor.
- Calculate the pitch of the loops, as well as the temperature of the coolant in the supply and return lines.
- Find out the length of the pipe in the circuit.
Before making further calculations, we want to caution against the use of underfloor heating as the main and only heating system. According to many experts, including Vladimir Sukhorukov, floor heating should work in conjunction with conventional batteries for the following reasons:
- water circuits warm a decent mass of concrete screed, and therefore are quite inert and slowly react to changes in coolant temperature;
- radiators respond well to manual and automatic adjustment, quickly respond to a rise or fall in the temperature of the mains water;
- in order to heat the room’s volume without batteries, the pipes must warm the surface to 28–33 ° C, creating a feeling of stuffiness in the room;
- accordingly, the heat carrier will have to be heated to 50–55 ° С; the economical temperature schedule of water floors is 45–35 ° С.
Hence the recommendation. Warm floors should be calculated for the most comfortable surface temperature of +26 ° C and additionally mount a radiator network that can function independently, separately from underfloor heating. It will warm the air to the desired temperature and will maintain it in automatic mode.
If you decide not to install convection heating batteries due to an increase in construction costs, you can still use the calculation below to find out the footage of the circuits, the diameter and the pitch of laying pipelines. Explanations of our expert regarding the installation of radiators:
Coolant flow rate and coating temperature
The proposed calculation method is based on a graphical method of solution. But the volume of water passing through the circuit for 1 hour, you need to know for the correct settings of the flowmeters of the distribution manifold, hydraulic calculation and selection of the circulation pump for productivity.
The consumption of heating water is calculated by the formula:
Explanation of symbols:
- G - the desired value of the flow, units - kg / h;
- Q - thermal power spent on heating the premises (calculated in the previous section), W;
- Δt is the temperature difference between the heat carrier in the supply and return branches, for a heating floor it is usually taken equal to 10 ° С.
Example. To heat a living room with an area of 15.75 m², you will need 15.75 x 130 = 2048 W of heat. The hourly flow rate of heated water will be G = 0.86 x 2048/10 = 176.13 kg / h.
To find out the surface temperature of the floors, it is necessary to know the type of coating, since tiles, linoleum and wooden parquet (laminate) pass the heat flux in different ways. Suppose, in the aforementioned living room, it is planned to lay linoleum, then we turn to the nomogram, where such parameters are reflected:
- the difference between the average temperature of the coolant and the air in the living room;
- specific heat transfer from 1 m² of floors;
- the corresponding surface temperature;
- graphs for pipe laying pitch from 10 to 35 cm.
To determine the degree of heating of the coating, select the nomogram compiled for linoleum. We look at the specific heat transfer - in the living room it is more than 120 W / m², which corresponds to a temperature of 31 ° C. Earlier, we agreed that this indicator is too large and take into account the optimal value - 26 ° C. Then the specific thermal power q will be 68 W / m².
The lack of heat recovered by radiators is easy to calculate. In our example, we multiply the found q value by the living room area, subtract the resulting figure from the previously calculated power indicator: 2048 W - 68 W / m² x 15.75 m² = 977 W.
Accordingly, the amount of coolant consumed by the floor system will change. Consumption will decrease to 0.86 x 1071/10 = 92.1 kg / h.
Note. Similar ready-made schedules are made for other types of coatings - tiles made of porcelain stoneware, laminate and thick flooring, nomograms are given throughout the article. Calculations of floor heating arranged in wooden floors with the “dry” method are carried out according to the schedules for ceramic tiles.
Laying pitch and water temperature
For floor heating of private houses and apartments, it is customary to lay pipes made of metal-plastic or cross-linked polyethylene with a diameter of 16 x 2 mm (DN10). The above nomograms are designed specifically for these polymeric materials.
The choice of the layout step will be made using the example of a living room of a one-story house:
- Using the same nomogram compiled for the synthetic coating (linoleum), we select a graph with an interval of 15 cm.
- From the point of intersection of the graph with the green line, we go down to the scale of temperature differences, we obtain tp = 19 ° C.
- We find the value of the average coolant temperature tav by the formula:
Here the designation tv shows the desired air temperature in the living room, taken +22 ° C. We consider tav: 19 + 22 = 41 ° C. Knowing that the temperature difference between the supply and return Δt is 10 degrees, it is easy to find out the temperature graph: 41 ± 5 = 46/36 ° С.
Please note: if you take a larger interval between the heating pipelines (for example, 20 cm), then the heat carrier will need to be heated more strongly. It is necessary to keep 48 ° С in the supply line, 38 ° С in the return line.
The calculation of the temperature graph will help to correctly select the three-way mixing valve, which must be installed on the collector of a water heated floor. When cooling the return water from the circuits to 36 degrees, it will mix the hot heat carrier from the gas (or other) boiler. Upon reaching 46 ° C, the valve will shut off the flow, and the pump will cause the water to rotate along the circuits until it cools again.
Pipe length and final results
Denoting the loop laying interval with the Latin letter b and converting units to meters, calculate the pipe length using the formula:
The letter F indicates the area of the room in square meters. The length of the pipe in the living room from our example will be L = 15.75 m² / 0.15 m = 105 m. Here we encounter the following problem: for the concrete monolith to warm evenly, the length of the circuit should not exceed 100 m, and the hydraulic resistance should be 20 kPa. It is required to put 105 m in the living room plus the length of the connections to connect the heating circuit to the comb.
An important point. Before performing the calculations, sketch a diagram with the plan of the house and take the place of the cabinet with the collector. In the drawing, the comb is in the corridor - the distance to all rooms is approximately the same.
How to solve the issue with a large pipe length:
- Divide the living room area into 2 heating circuits of the same size.
- The length of one pipeline should be determined taking into account the connection to the collector - (105 + 5) / 2 = 55 m.
- Make a deformation seam between the two monoliths, allowing the plates to expand from heating without destroying each other.
To properly fill 2 plates with a deformation seam, carefully study the presented diagram. The base and warming with foam plastic for monoliths are common, only the upper part of the “pie” is separated - a screed with pipes inside.
Tip. If the length of the circuits does not exceed 60 meters, instead of an additional pump and a three-way valve, it is recommended to put RTL thermal heads on the comb of warm floors. The element restricts the return flow until the coolant temperature reaches the calculated temperature (in this example, 36 ° C).
It remains to calculate the parameters of the floor contours in the remaining rooms of a one-story house. Suppose that the bedroom and the nursery are covered with a laminate, the kitchen with ceramic tiles. Using nomograms for the indicated coatings, we carry out calculations, the results are entered in the general table.
Note. The temperature of the flooring in the nursery is limited to 24 ° C according to the requirements of sanitary standards. The proposed calculation methodology is published in the book of V.V. Pokotilov "Water Heating Systems", published in 2008.
Features of electric floor systems
The technology for the preparation and layout of electric heating elements differs from the arrangement of water circuits and depends on the type of selected heating elements:
- resistive cables, carbon rods and cable mats may be laid “dry” (directly under the cover) and “wet” (under the screed or tile adhesive);
- The carbon infrared films shown in the photo are best used as a substrate for the coating without screed, although some manufacturers allow laying under the tiles.
For reference. Self-regulating rod systems are carbon heating elements connected in parallel by two conductors. In the event of a burnout of one rod, the remaining elements will increase the heating power and continue to heat the room.
3 features are inherent in electric heating elements:
- uniform heat transfer along the entire length;
- the heating intensity and surface temperature are controlled by a temperature regulator that focuses on the readings of the sensors;
- intolerance to overheating.
Self-regulating rods calmly carry such things, but another factor begins to influence here - buying and laying expensive carbon heaters under furniture is irrational.
Selection of cable and film heaters
In connection with the above points, the calculation of electric heating is somewhat simplified, the parameters of the cable floor heating are determined as follows:
- Calculate the amount of heat needed to heat a particular room (see section one).
- Draw the layout of the room with the location of stationary furniture and household appliances. Make a drawing to scale to the actual dimensions of cabinets, washing machines and so on.
- Count the free area of the room by taking the square of the occupied areas.
- The previously found amount of heat should be distributed over the remaining area. Divide the required power by the square of the free area - get heat transfer from 1 m².
- Resistive cables and mats with a thermal power of 9-25 W / m. n. are sold a fixed length. Select the heating element according to the required heat transfer from the manufacturer’s catalog.
- Divide the square of the free area by the length of the selected product - you will find out the cable layout step.
An example of calculating the bathroom of a one-story house with an area of 6 m², of which 2.5 m² are occupied by a bathtub, sink and cabinet. The square of the free area is 3.5 m², the required thermal power is 600 watts. According to the catalog of the famous Devi brand, we select a two-core heating cable of the DEVIflex 18T brand with a length of 37 meters with a heat transfer of 622 watts. Divide 3.5 m² by 37 m, we get a pitch of 0.095 m, rounded - 10 cm.
Note. It’s even easier to select cable mats - the manufacturer indicates the area occupied by the heating element. For the bathroom, a product with a capacity of 635 W of the brand DEVImat 200T, designed for a quadrature of 3.45 sq. M., Is suitable.
Similarly calculated and selected film heaters laid under the floor covering. A small nuance: when installing a carbon film or resistive cable in living rooms, a minimum spacing of 150 mm from the partitions is made. These stripes along the walls will also have to be taken away from the general quadrature. On loggias, balconies and bathrooms, this indentation is taken equal to the laying pitch (in the example - 10 cm).
Conclusion
The above calculation method does not mention the insulation of the “pie” of the warm floor from the ground or floor. The reason is simple: thermal insulation must be present in any case, on the ground - 10 cm of polystyrene foam or dense mineral wool, on the ceiling - 20 mm of extruded polystyrene foam. An accurate calculation of the material and thickness of the insulation is an extensive topic for a separate publication.
If the course of the calculations seemed too complicated for you, try using online tools - calculators posted on various sites. But remember - the results of the calculations must be checked using specialized programs or the proposed graphical method. An example of working with the software package from the Herz Armaturen brand is presented in the video.