The subtleties of calculating a warm floor

The subtleties of calculating a warm floor

Home improvement should start with an appropriate calculation. He will give a rough idea of ​​all the characteristics of the planned work and will reveal the question of the profitability of the idea as a whole. The calculation is especially important in the case of installing underfloor heating in a private house..


Underfloor heating is a heating equipment, and its stable operation is extremely important. It depends not only on the quality of installation, but also on the materials used. The most important component of the efficiency of the floor is the reliable calculation of all operating parameters. It is also clear from school tasks that it is difficult to calculate something without understanding the meaning, so you need to understand the principles of the heating system and the peculiarities of its placement. There are two types of underfloor heating:

  • warm floors with water heat carrier;
  • electric underfloor heating.

The construction of water-heated floors is designed in such a way that heating occurs due to the heat given off by heating circuits, consisting of small diameter water pipes. These pipes are laid under the floor surface and looped around the heating unit – the boiler, which is responsible for heating. In most cases, the system is supplemented by devices that provide comfortable heating, as well as control devices.

Underfloor heating, powered by electricity, heats the floor surface using a similar technology. Instead of tubes, a special two-core cable is laid in the floor structure, which is a heat-emitting conductor. The radiation intensity is regulated by a special thermostat.

You need to have an idea of ​​how this system is located in a heated room. For ease of understanding, you need to think of the floor as a layer cake. The first frame layer is usually a concrete slab on which a roll of waterproofing material is laid. Next, a material with a low resistance to heat transfer is applied, for example, expanded polystyrene, which is insulated with foil. Finally, all this is covered with a screed, into which the heating pipes of the warm floor are mounted..

The calculation of underfloor heating is a rather serious task. You need to carry it out as carefully as possible. As a result, this will allow you to get a complete picture of the required characteristics for the pump, the length of the heating pipes, the amount of heat radiation for specific cases, and much more. Of course, if you have money, you can pay for a range of services to specialists, but it’s better to keep everything under your control..

Despite the fact that the calculation is not easy, following the step-by-step instructions, it will not be difficult to cope with it.

Calculation table in a private house

Underfloor heating can serve as the main source of heating in a room or as a means for heating only the floor surface. Depending on what specific functions are planned to be assigned to the underfloor heating system, its heat transfer is calculated. In addition, the input data are also the geometric and structural characteristics of the room. First, you need to find out how much heat will be lost due to the design features of the room. Without knowing this parameter, it is impossible to understand how much heat the heating circuit should give off, which in general is the focus of the calculation.

Only after this step, you can select the rest of the system parameters, such as:

  • required pump power;
  • power of an electric boiler or gas boiler;
  • material and thickness of the coolant tubes;
  • length of contours.

In the event that the heating system in the house functions perfectly, and only insulation of the floor surface is required from the underfloor heating system, the main calculated value will be the footage of the heated room. Heat losses and the length of the pipelines to be laid for a warm water floor will mainly depend on the geometry of the heated surface. For the calculation to be absolutely accurate, you need to take into account the climate, construction features, number of storeys and much more. As a result, you get a rather complex thermal calculation..

It may turn out that the consumer is not a professional, but still wants to save money on home improvement. In this case, it is possible to use the average heat consumption indicators for private houses. Heating a house with a warm floor has been used for a long time, and a special table has been formed by experienced specialists. It shows the required amount of heat for the intended room in which the heating circuits of the water floor will be placed..

Power formula

In most cases, underfloor heating is used as a system that replaces heating radiators. Then the calculation, of course, will become more complicated, because you need to take into account all the factors. In order to be able to heat the entire internal volume of the room, it is necessary to have information about the heat loss of the room. Only then, knowing the capacity of the heating circuit, can you start designing it. So, the calculation itself looks like this:

Mk = 1.2 x Q, where Mk is the required heat transfer power of the heating circuit, Q is the same heat loss, and 1.2 is the error coefficient.

It is clear from the formula that the target parameter is the temperature of the coolant in the circuit, to determine which it is necessary to calculate the heat loss. To determine them, you will need to walk around the house with a tape measure. It is necessary to measure the area and thickness of all enclosing objects: walls, floors, windows, doors, and so on. To take into account the structure of the material of all objects, you need a coefficient characterizing the thermal conductivity of individual materials (λ). Accordingly, you need to know what is made of what is to be calculated, be it a wall, door or ceiling. All popular building materials and their coefficients are shown in the following table:

Heat loss are calculated separately for each barrier element of the room, since each object has different properties. The calculation is performed according to the following formula:

Q = (1 / R) x (tvn-tn) x (1 + ∑β) x S, where R is the temperature resistance of the raw material from which the enclosing structure is made, t is the temperature of the structure, the indices, respectively, mean the external and internal temperatures, S – the geometric area of ​​the element, β – climatic heat losses depending on the cardinal direction, which must be taken into account.

The calculated heat losses for individual elements are summed up as a result. So, the resulting total heat loss of the room is substituted into the formula for calculating Mk – the heat transfer power of the circuit.

For example, we will calculate the required heat transfer of the circuit for a block room of 20×20 m, the width of the walls of which is 2.5 mm. Based on the fact that the thermal resistance of foam concrete blocks is 0.29 (W / m x K), we obtain the calculated value Rpb = 0.25 / 0.29 = 0.862 (W / m x K). The walls are plastered with a layer of 3 mm, which means that Rpc = 0.03 / 0.29 = 0.1 (W / m x K) must be added to the resulting resistance. This means that the total thermal resistance of the wall is Rst = 0.1 + 0.862 = 0.962 (W / m x K). Next, we calculate the heat loss using the above formula:

Q = (1 / 0.962) x (20 – (-10)) x (1 + 0.05) x 40 = 1309 W.

We calculate the heat loss through the ceiling, door and windows in exactly the same way. We summarize everything obtained and substitute it into the formula to determine the power of the heating circuit. To the resulting value, add 10%, which will correct for air infiltration. Any calculator can handle this..

How to calculate the styling correctly?

After finding out the power required for a warm floor, you can familiarize yourself with the intricacies of the location of its contour. Next, it remains only to calculate the required length of the contour, which will help to get an idea of ​​the upcoming costs. For clarity, you need to make a sketch on graph paper. The drawing must be carried out taking into account the pipe spacing and scale factors.

A step is a measured interval of voids between pipes, it must be selected in accordance with several conditions:

  • when moving on the floor, the human foot should not feel the temperature difference, So, if the step is too large, then the surface will be heated by stripes.
  • The step should be chosen in such a way that the pipe performs its function as economically and efficiently as possible..

For error-free pipeline installation, you need to understand the advantages and disadvantages of the types of installation used. Currently, 4 schemes are used for the installation of a heating pipeline:

  • “Snail (spiral)” – the most demanded option, because such laying ensures a uniform distribution of thermal energy. Location occurs from the periphery to the center with a constant decrease in radius, and then to the other side. When using this method, the step length can be any value, starting from 10 mm.

Also, this method is the easiest in terms of installation, there are no restrictions due to the shape of the room..

  • “Snake” Is a rather unpopular method of contouring. A huge disadvantage is that the connection to the supply unit occurs on one side, therefore, there is a significant temperature difference. The surface of the floor will be colder the further you are from the boiler. The second significant disadvantage of the “snake” is the complexity of installation. This arrangement provides for 180 degree bends in the pipe. As a result, the annular spacing should be increased to 200 mm, while the universal value is considered to be 150 mm..

  • “Corner snake”. The warm flow spreads from the corner where the boiler is located. The method is not popular because the temperature spreads out in a gradient, which, in fact, creates the effect of the “sun”. The closer you are, the warmer.
  • “Double snake” is a modification of the usual “snake”. The difference is that heat losses are compensated. It does this by circulating the flow in both directions. Laying in this way is just as difficult. “Snake” is used for small spaces, such as a bathroom.

All of the above methods can be combined with each other. Small areas are sometimes covered with a “snake”, and elements that do not need to be heated are circled with a “spiral”. Sometimes combined pipe laying methods provide the lowest material cost and minimum investment. Now, having the necessary information, you can start calculating the required length of the pipeline. The calculation is carried out according to a simple formula:

L = 1.1 x S \ N. The above formula reflects the dependence of the length of the heating pipe (L) on the area of ​​the circuit (S), taking into account the step (N). A factor of 1.1 is necessary to take into account the stock of the pipe for bends. At the end, you should also take into account the segments that will be current and countercurrent to connect the stack with the boiler..

To avoid misunderstandings, we will calculate the length of the heating circuit for a living room of 25 sq. m. In order to remove the limitation in the dimension of the step, we will give preference to the method of spiral laying and choose a step of 0.15 meters. In this case, it turns out that the length of the pipeline being laid is L = 1.1 x 25 / 0.15 = 183.4 m.

Let’s say the underfloor heating system is powered by a comb, which is located 5 m from the circuit. When calculating, it is necessary to double this distance, since the collector has a counterflow. Therefore, the resulting length of the contour will be L = 183.4 + 5 + 5 = 193.4 m.

Professional advice

Having dealt with the calculation, you can go with the results to specialists and concretize their task. There is no need to rush, it will not be superfluous to familiarize yourself with some of the nuances. They can only be encountered when installing a warm floor not for the first time. Those who know this business well recommend:

  • when drawing a contour, try to figure out how to use as little pipe as possible. With a short pipeline length, there will be no tangible resistance, and therefore no pressure drops, that is, there will be no need to spend money on a powerful pump.

In general, a short pipe is less costly..

  • When the calculation of the length of the pipeline is completed, the obtained value must be compared with the permissible length of the circuit. It depends on the diameter of the pipe to be laid. If the diameter is 16 mm, then the permissible value for the length of the contour is 100 m, and if the diameter is 20 mm, then the limitation will be 120 m..
  • The annular spacing is taken in the optimal range, but depends on the diameter of the heating pipe.

  • When designing the installation, it must be remembered that not all areas in the room have the same need for heating, therefore, plan the location of the pipe more tightly near windows and door structures. This will provide intense heating there..
  • In cases where the projected area exceeds 40 sq. m, you need to connect the second circuit, since the operation of a single-circuit underfloor heating in large rooms is ineffective.

Thus, the calculation of the warm floor can be done independently..

It is recommended to perform the calculation both manually using the formulas and on a special calculator, and then compare the resulting values.

For more information on this issue, you can find out by watching the video below.

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