Calculation of heated floors based on heat loss, determination of pipe footage and other data

Air 0 40 Supply 0 80 Return 0 80
Calculation results

Materials

Floor surface temperature

Heat flow

Coolant

Supply temperature / return temperature

Supply temperature—temperature of the coolant in the supply manifold. Those. at the entrance to the heated floor circuit.

Return temperature - the temperature of the coolant in the return manifold (at the outlet of the circuit).

In order for a warm floor to heat a room, it must give off heat, i.e. The supply temperature must be higher than the return temperature. It is optimal if the difference in supply and return temperatures is 10°C (for example, supply - 45°C, return - 35°C).

To heat the room, the supply temperature must be higher than the desired room temperature.

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Features of electrical floor systems

The technology for preparing and laying out electric heating elements differs from the design of water circuits and depends on the type of heating elements selected:

• resistive cables, carbon rods and cable mats can be laid “dry” (directly under the coating) and “wet” (under screed or tile adhesive);
• carbon infrared films shown in the photo are best used as a substrate under a coating without pouring a screed, although some manufacturers allow installation under tiles.

For reference. Self-regulating rod systems are carbon heating elements connected in parallel by two conductors. If one rod burns out, the remaining elements will increase the heating power and continue to heat the room.

Electric heating elements have 3 features:

• uniform heat transfer along the entire length;
• the heating intensity and surface temperature are controlled by a thermostat based on sensor readings;
• intolerance to overheating.

The last property is the most unpleasant. If in a section of the circuit the floors are filled with furniture without legs or stationary household appliances, heat exchange with the surrounding air will be disrupted. Cable and film systems will overheat and will not last long. All the nuances of this problem are covered in the next video:

Self-regulating rods easily tolerate such things, but another factor begins to influence here - it is irrational to buy and install expensive carbon heaters under furniture.

Length of underfloor heating supply line

This is the sum of the pipe lengths from the supply manifold to the beginning of the heated floor circuit and from the end of the circuit to the return manifold.

When placing the underfloor heating collector in the same room as the underfloor heating, the influence of the supply line is negligible. If they are located in different rooms, then the length of the supply line can be large and its hydraulic resistance can be half the resistance of the entire circuit.

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Selection of cable and film heaters

In connection with the above points, the calculation of electric heating is somewhat simplified; the parameters of a cable heated floor are determined as follows:

1. Calculate the amount of heat needed to heat a specific room (see section one).
2. Draw the layout of the room with the location of stationary furniture and household appliances. Make the drawing to scale to the actual dimensions of cabinets, washing machines, and so on.
3. Calculate the free area of ​​the room by subtracting the square footage of the occupied areas.
4. The previously found amount of heat should be distributed over the remaining area. Divide the required power by the square footage of the free area - get the heat transfer from 1 m².
5. Resistive cables and mats with a thermal power of 9-25 W/m. items are sold in fixed lengths. Select a heating element from the manufacturer's catalog according to the required heat transfer.
6. Divide the square footage of the free section by the length of the selected product - you will find out the cable layout pitch.

Scheme of underfloor electric heating of a bathroom
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 footage of the free area is 3.5 m², the required thermal power is 600 W. According to the catalog of the famous Devi brand, we select a two-core heating cable of the DEVIflex 18T brand, 37 meters long with a heat output of 622 W. We divide 3.5 m² by 37 m, we get a laying step of 0.095 m, rounded - 10 cm.

Note. It is even easier to select cable mats - the manufacturer indicates the area occupied by the heating element. For the bathroom, a product with a power of 635 W of the DEVImat 200T brand, designed for an area of ​​3.45 square meters, is suitable.

Film heaters placed under the floor covering are calculated and selected in a similar way. A small nuance: when installing carbon film or resistive cable in living rooms, a minimum distance of 150 mm is made from the partitions. These stripes along the walls will also have to be subtracted from the total square footage. On loggias, balconies and bathrooms, this indentation is taken to be equal to the laying step (in the example - 10 cm).

Screed thickness over underfloor heating pipes

The purpose of the screed over the pipes of heated floors is to absorb the load from people and objects in the heated room and evenly distribute the heat from the pipes over the floor surface.

The minimum permissible thickness of the screed above the pipe is 30 mm with reinforcement. With a smaller thickness, the screed will have insufficient strength. Also, the small thickness of the screed does not ensure uniform heating of the floor surface - stripes of hot floor appear above the pipe and cold between the pipes.

It is not worth pouring a screed thicker than 100 mm, because... this increases the inertia of heated floors and eliminates the possibility of quickly adjusting the floor temperature. With a large thickness, a change in the temperature of the floor surface will occur after several hours, or even days.

Based on these conditions, the optimal thickness of the heated floor screed is 60-70 mm above the pipe. Adding fiber and plasticizer to the solution allows you to reduce the thickness to 30-40 mm.

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Calculation rules

To install a heating system on an area of ​​10 square meters, the best option would be:

• use of 16 mm pipes with a length of 65 meters;
• the flow rate of the pump used in the system cannot be less than two liters per minute;
• the contours must be of equal length with a difference of no more than 20%;
• the optimal distance between pipes is 15 centimeters.

It should be taken into account that the difference between the temperature of the surface and the coolant can be about 15 °C.

The optimal method for laying a pipe system is represented by a “snail”. It is this installation option that promotes the most uniform distribution of heat over the entire surface and minimizes hydraulic losses, which is due to smooth turns. When laying pipes in the area of ​​external walls, the optimal step is ten centimeters. To perform high-quality and competent fastening, it is advisable to carry out preliminary markings.

Table of heat consumption of various parts of the building

Average floor surface temperature

This parameter is the main criterion for calculating a heated floor in terms of comfort for residents. It represents the average value between the maximum and minimum floor temperature.

According to standards, in rooms with constant presence of people (living rooms, offices, etc.), the average floor temperature should not be higher than 26°C. In rooms with high humidity (bathrooms, swimming pools) or where people are not constantly present, the floor temperature can be up to 31°C.

A floor temperature of 26°C does not provide the expected comfort for the feet. In a private house, where no one has the right to tell the owner what temperature to heat the home at, you can set the average floor temperature to 29°C. At the same time, your feet will feel comfortable warmth. You should not raise the temperature above 31°C - this leads to drying out the air.

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Find out the required thermal power

To calculate all the parameters of a future heated floor - water or electric - it is necessary to determine how many watts of heat to supply to heat a particular room. We suggest calculating the required heating power in the simplest way - by area or volume of the room.

Advice. Installing underfloor heating circuits is not a cheap pleasure. The price of work, taking into account materials and components, ranges from 5-8 USD. 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 design, require all calculations from the contractors, then compare the results.

As an example, we use the layout of a small one-story house of 100 m² (according to external measurements), shown in the drawing. Please note that corner rooms with light openings and external walls will lose much more heat in winter than internal ones - a corridor, a bathroom and a hallway. The nuance is taken into account in the proposed methodology:

1. By measuring and multiplying the lengths, find out the square footage of each room.
2. Multiply the area of ​​rooms with one outer wall and a light opening by 0.1 kW. This category also includes central rooms (in the example, the hallway, bathroom and corridor).
3. Heating rooms located in the corners of the building will require more thermal energy. The square footage of a room with two external walls and a window should be multiplied by 0.12 kW (kitchen and children's room).
4. If there are 2 or more window openings in a corner room, the area is multiplied by 0.13 kW (living room and bedroom on the layout).

The calculation results are the required heat output of heating circuits or radiators in kilowatts separately for each room. With the obtained figures, you can proceed to the next stage of calculation.

Note. The indicated values ​​are valid for the central zone of the Russian Federation and the Republic of Belarus. For dwellings located in the south, the thermal power values ​​must be multiplied by a factor of 0.7. In the northern regions, an increasing factor of 1.5-2 is applied to the results.

The above method 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.

Determination of heating heat transfer by volume of rooms with ceilings of 3 m and above

Calculation of heat loss at home

Before calculating a water heated floor, you must first calculate the heat loss of the house. Heat loss is the amount of heat that a room loses per unit of time. To reduce heat loss, heating devices are used, for example radiator heaters, heating pipes, and heated floors. In addition, it is possible to reduce heat loss by installing double-glazed windows and insulating walls with various materials that can retain heat inside the room.

Calculation of heat loss is an important parameter when designing a residential premises. In this case, it is necessary to take into account:

• room area;
• area of ​​all windows;
• ceiling height;
• number of external walls;
• temperature from the outside of the room;
• window type;
• thermal insulation of walls;
• type of room located above.

Basically, heat loss depends on the difference in temperatures outside and inside the room, as well as on the degree of thermal insulation of windows, walls, and partitions. To more accurately calculate heat loss, you can use one of the many online calculators. They are quite simple and easy to use; just enter the required values ​​and the calculation will be done automatically. In such calculators it is possible to calculate heat loss through windows, ceilings, walls, and floors. This will allow you to obtain detailed information on the basis of which the power of the heating equipment should be calculated.

It is generally accepted that a warm floor will cope if the heat loss does not exceed 100 W per meter of area. If this indicator is exceeded, you will have to resort to installing an additional heating device.

What is a calculator for?

For heated floors, it is necessary to make accurate calculations, since the materials are high in cost, but the payback can also be seen after several months of operation. It is best to do all calculations using a special calculator. This calculation can be done directly online.

With it you can make the thermal parameters of the system, take into account the diameter and length of the pipe. The calculator will help you calculate the material, regardless of how it will be sold: using the wet method or the dry method.

Another advantage is that if the maximum permissible parameter values ​​are too high, the calculator will generate errors.

First of all, it is worth considering that heat flows must go from bottom to top, then the conditions in the room will be favorable for humans. A warm floor will not take up much space, and all heating systems are also placed compactly.

We recommend: How to install Onor heated flooring?

If underfloor heating systems are implemented correctly, they will not only heat well, but also, using high-quality materials, will last a long time. The service life can reach 75 years.

Sometimes a heated floor system is the only way to heat a room; if it is not enough, then additional sources are installed. The calculator will calculate everything exactly for a given room.

Number of circuits

The table shows the optimal values ​​for the length and number of circuits for each pumping and mixing unit.

Calculating the circulation pump

To make the system economical, you need to select a circulation pump that provides the required pressure and optimal water flow in the circuits. Pump passports usually indicate the pressure in the circuit of the longest length and the total coolant flow in all loops.

The pressure is influenced by hydraulic losses:

∆ h = L*Q²/k1 , where

• L —contour length;
• Q - water consumption l/sec;
• k1 is a coefficient characterizing losses in the system; the indicator can be taken from hydraulic reference tables or from the equipment passport.

Knowing the pressure value, calculate the flow rate in the system:

Q = k*√H , where

k is the flow coefficient. Professionals assume the flow rate for every 10 m² of a house is within 0.3-0.4 l/s.

Among the components of a warm water floor, a special role is given to the circulation pump. Only a unit whose power is 20% higher than the actual coolant flow will be able to overcome the resistance in the pipes

The figures regarding pressure and flow rates indicated in the passport cannot be taken literally - this is the maximum, but in fact they are influenced by the length and geometry of the network. If the pressure is too high, reduce the length of the circuit or increase the diameter of the pipes.

Results

Having carefully made all the calculations online, you can double-check them by calculating them yourself or asking a specialist to do it. It is important to remember that calculations are the initial stage, on which the correct installation of the entire system and its operation in the future depends.

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