Calculation of pipes for floor heating: formulas, choice of installation step, how to determine the flow

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Despite the complexity of installation, floor heating using a water circuit is considered one of the most cost-effective methods of heating the room. In order for the system to function as efficiently as possible and not to fail, it is necessary to correctly calculate the pipes for a heated floor — determine the length, loop pitch, and contour laying scheme.

From these indicators depends largely on the comfort of using water heating. These questions we will analyze in our article - we will tell you how to choose the best option for pipes, taking into account the technical characteristics of each type. Also, after reading this article, you will be able to correctly choose the installation step and calculate the required diameter and length of the contour of the heated floor for a particular room.

The content of the article:

  • Parameters for calculating the thermal circuit
    • Pipe Coverage Area
    • Heat flow and coolant temperature
    • Type of flooring
  • Evaluation of technical properties when choosing a pipe
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    • Option # 1 - crosslinked polyethylene (PEX)
    • Option # 2 - metal plastic
    • Option # 3 - copper pipes
    • Option # 4 - polypropylene and stainless steel
  • Possible ways of laying the contour
    • Method # 1 - Snake
    • Method # 2 - Snail or Spiral
  • Pipe calculation method
    • Principles of construction of the scheme
    • Basic formula with explanations
    • Thermal calculation with the definition of the contour pitch
    • Final contour length selection
  • A specific example of the calculation of the heating branch
    • Step 1 - calculation of heat loss through structural elements
    • Step 2 - heat to heat + total heat loss
    • Step 3 - the required power of the thermal circuit
    • Step 4 - determination of the laying step and the length of the contour
  • Conclusions and useful video on the topic

Parameters for calculating the thermal circuit

At the design stage, it is necessary to solve a number of issues that determine design features underfloor heating and mode of operation - to choose the thickness of the screed, the pump and other necessary equipment.

Technical aspects of the organization of the heating branch are largely dependent on its purpose. In addition to the appointment, for the exact calculation of the footage of the water circuit, a number of indicators will be needed: the area of ​​the coating, the density of the heat flow, the temperature of the heat carrier, the type of floor covering.

Pipe Coverage Area

When determining the dimensions of the base for pipe laying, a space is taken that is not cluttered with large appliances and built-in furniture. It is necessary to think in advance about the layout of objects in the room.

Water floor heating

If the water floor is used as the main supplier of heat, then its capacity should be enough to compensate for 100% of heat loss. If the coil is an addition to the radiator system, then it is obliged to cover 30-60% of the heat cost of the room.

Heat flow and coolant temperature

The heat flux density is a calculated indicator characterizing the optimal amount of heat energy for heating a room. The value depends on a number of factors: thermal conductivity of walls, floors, glazing area, the presence of insulation and the intensity of air exchange. Based on the heat flow, the step of laying the loop is determined.

The maximum temperature of the coolant - 60 ° C. However, the thickness of the screed and floor covering knock down the temperature - in fact on the surface of the floor there is about 30-35 ° C. The difference between thermal indicators at the inlet and outlet of the circuit should not exceed 5 ° С.

Type of flooring

Finishing affects system performance. The optimal thermal conductivity of tile and porcelain - the surface heats up quickly. A good indicator of the efficiency of the water circuit when using laminate and linoleum without a heat-insulating layer. The lowest thermal conductivity of a wooden coating.

The degree of heat transfer depends on the fill material. The system is most effective when using heavy concrete with natural aggregate, for example, sea pebbles of small fraction.

Cement-sand screed

Cement-sand solution provides an average level of heat transfer when the coolant is heated to 45 ° C. Efficiency contour significantly decreases when the device semi-dry screed

When calculating pipes for underfloor heating, it is necessary to take into account the established standards for the temperature regime of coating:

  • 29 ° С - living room;
  • 33 ° С - rooms of high humidity;
  • 35 ° С - passage zones and cold belts - sections along the end walls.

An important value for determining the density of laying the water circuit will play the climatic features of the region. When calculating heat losses, it is necessary to take into account the minimum temperature in winter.

As practice shows, pre-warming of the whole house will help reduce the load. It makes sense to first insulate the room, and then proceed to the calculation of heat loss and parameters of the pipe circuit.

Evaluation of technical properties when choosing a pipe

Due to non-standard operating conditions, high requirements are placed on the material and size of the water floor coil:

  • chemical inertnessresistance to corrosive processes;
  • having a completely smooth inner coatingnot prone to the formation of lime growths;
  • strength - inside the walls are constantly affected by the coolant, and outside - the screed; the pipe must withstand pressure up to 10 Bar.

It is desirable that the heating branch had a small proportion. Pie of a water floor and without that exerts a significant load on the floor, and a heavy pipeline only exacerbates the situation.

Welded metal

According to SNiP in closed heating systems, the use of welded pipes is prohibited, regardless of the type of weld: spiral or straight

Three categories of pipe rolled products meet one or another of the listed requirements: cross-linked polyethylene, metal-plastic, and copper.

Option # 1 - crosslinked polyethylene (PEX)

The material has a net-rich cellular molecular structure. Modified from ordinary polyethylene is characterized by the presence of both longitudinal and transverse ligaments. Such a structure increases the specific gravity, mechanical strength and chemical resistance.

The water circuit made of PEX pipes has several advantages:

  • high elasticity, allowing to lay a coil with a small bend radius;
  • security - when heated, the material does not emit harmful components;
  • heat resistance: softening - from 150 ° С, melting - 200 ° С, burning - 400 ° С;
  • keeps structure with temperature fluctuations;
  • damage resistance - biological destructors and chemical reagents.

The pipeline retains its original throughput capacity — no sediment is deposited on the walls. The estimated service life of the PEX circuit is 50 years.

Crosslinked polyethylene

The disadvantages of cross-linked polyethylene include: fear of sunlight, the negative effect of oxygen when it penetrates inside the structure, the need for rigid fixation of the coil when laying

There are four groups of products:

  1. PEX-a - peroxide crosslinking. Achieved the most durable and uniform structure with a density of bonds up to 75%.
  2. PEX-b - silane crosslinking. The technology uses silanides - toxic substances that are not allowed for household use. Manufacturers of plumbing products replace it with a safe reagent. To install valid pipes with hygienic certificate. The density of crosslinking is 65-70%.
  3. PEX-c - radiation method. Polyethylene is irradiated with gamma rays or an electron. As a result, bonds are sealed to 60%. Disadvantages PEX-c: insecurity of use, uneven stitching.
  4. PEX-d - nitriding. The reaction to create a grid proceeds at the expense of nitrogen radicals. The output is a material with a crosslink density of about 60-70%.

The strength characteristics of PEX pipes depend on the method of crosslinking polyethylene.

If you stopped on pipes made of cross-linked polyethylene, we recommend that you familiarize yourself with arrangement rules floor heating systems of them.

Option # 2 - metal plastic

The leader of the pipe rolled for arranging underfloor heating - metal-plastic. Structurally, the material includes five layers.

Metal pipes

The inner coating and outer shell are high-density polyethylene, which gives the pipe the necessary smoothness and heat resistance. Intermediate layer - aluminum gasket

The metal increases the strength of the line, reduces the rate of thermal expansion and acts as an anti-diffusion barrier - it blocks the flow of oxygen to the coolant.

Features of metal pipes:

  • good thermal conductivity;
  • the ability to retain a given configuration;
  • working temperature with preservation of properties - 110 ° C;
  • low specific weight;
  • noiseless movement of the coolant;
  • safety of use;
  • corrosion resistance;
  • Duration of operation - up to 50 years.

The lack of composite pipes - the inadmissibility of bending on the axis. With repeated twisting there is a risk of damage to the aluminum layer. We recommend to get acquainted with proper mounting technology plastic pipes that will help avoid damage.

Option # 3 - copper pipes

On the technical and operational characteristics of the yellow metal will be the best choice. However, its demand is limited to high cost.

Copper contour

Compared to synthetic pipelines, the copper circuit benefits in several ways: thermal conductivity, thermal and physical strength, unlimited bending variation, absolute gas impermeability

In addition to the high cost, copper piping has an additional negative - complexity montage. To bend the contour, you need a press machine or pipe bender.

Option # 4 - polypropylene and stainless steel

Sometimes the heating branch is made of polypropylene or stainless corrugated pipes. The first option is affordable, but fairly tough to bend - the minimum radius of the eight diameters of the product.

This means that pipes with a size of 23 mm will have to be placed at a distance of 368 mm from each other - an increased installation pitch will not ensure uniform heating.

Stainless corrugated pipes

Stainless pipes have high thermal conductivity and good flexibility. Minuses: fragility of sealing rubber, creation of corrugated strong hydraulic resistance

Possible ways of laying the contour

In order to determine the flow of the pipe for the arrangement of a heated floor, it is necessary to determine the layout of the water circuit. The main task of layout planning is to ensure uniform heating, taking into account cold and unheated areas of the room.

Pipe laying methods

The following layouts are possible: snake, double snake and snail. When choosing a scheme, it is necessary to take into account the dimensions, the configuration of the room and the location of the external walls.

Method # 1 - Snake

The coolant is fed to the system along the wall, passes through the coil and returns to distribution manifold. In this case, half of the room is heated with hot water, and the remainder is cooled.

When laying a snake it is impossible to achieve uniformity of heating - the temperature difference can reach 10 ° C. The method is applicable in narrow spaces.

Snake pipe laying

The scheme of the corner snake is best suited if it is necessary to maximally insulate the cold zone near the end wall or in the hallway.

Double snake allows you to achieve a softer transition of temperatures. Forward and reverse loop runs parallel to each other.

Method # 2 - Snail or Spiral

This is considered the optimal scheme, ensuring uniform heating of the floor covering. Forward and reverse branches are stacked alternately.

Snail pipe layout

An additional advantage of “shells” is the installation of a heating circuit with a smooth bend. This method is relevant when working with pipes of insufficient flexibility.

In large areas implement a combined scheme. The surface is divided into sectors and each develops a separate circuit leading to a common collector. In the center of the room, the pipeline is laid out by a snail, and along the outer walls - by a snake.

We have another article on our website in which we have reviewed in detail installation layouts warm floor and led recommendations for choosing the best option depending on the characteristics of a particular room.

Pipe calculation method

In order not to get confused in calculations, we propose to divide the solution of the issue into several stages. First of all, it is necessary to evaluate the heat loss of the room, determine the laying step, and then calculate the length of the heating circuit.

Principles of construction of the scheme

Starting the calculations and creating a sketch, you should familiarize yourself with the basic rules for the location of the water circuit:

  1. It is advisable to lay the pipes along the window opening - this will significantly reduce the heat loss of the building.
  2. The recommended coverage area of ​​one water circuit is 20 square meters. In large premises it is necessary to divide the space into zones and for each to lay a separate heating branch.
  3. The distance from the wall to the first branch is 25 cm. The permissible pitch of the pipe turns in the center of the room is up to 30 cm, on the edges and in cold zones - 10-15 cm.
  4. Determining the maximum pipe length for underfloor heating should be based on the diameter of the coil.

For a contour with a cross section of 16 mm, a maximum of 90 m is permissible, the restriction for a pipeline 20 mm thick is 120 m. Compliance with the norms will ensure normal hydraulic pressure in the system.

Pipe flow

The table shows the estimated flow of the pipe, depending on the pitch of the loop. To obtain updated data, take into account the reserve for turns and the distance to the collector.

Basic formula with explanations

The calculation of the length of the contour of the heated floor is performed according to the formula:

L = S / n * 1.1 + k,

Where:

  • L - the desired length of the heating line;
  • S - covered floor area;
  • n - laying step;
  • 1,1 - standard factor of ten percent bending margin;
  • k - remoteness of the collector from the floor - take into account the distance to the wiring circuit on the flow and return flow.

Decisive importance will cover the area of ​​coverage and step turns.

Contour layout plan

For clarity, on paper it is necessary to draw up a floor plan indicating the exact dimensions and mark the passage of the water circuit.

It should be remembered that the placement of heating pipes is not recommended for large appliances and built-in furniture. The parameters of the designated items must be subtracted from the total area.

To find the optimal distance between the branches, it is necessary to carry out more complex mathematical manipulations in terms of heat loss from the room.

Thermal calculation with the definition of the contour pitch

The density of placement of pipes directly affects the amount of heat flow from the heating system. To determine the required load, it is necessary to calculate the heat costs in winter.

Room heat loss

Thermal costs through the structural elements of the building and ventilation should be fully compensated by the generated heat energy of the water circuit.

The power of the heating system is determined by the formula:

M = 1.2 * Q,

Where:

  • M - loop performance;
  • Q - total heat loss of the room.

The value of Q can be decomposed into its components: energy consumption through the building envelope and the costs caused by the operation of the ventilation system. We will understand how to calculate each of the indicators.

Heat loss through building elements

It is necessary to determine the heat energy consumption for all enclosing structures: walls, ceilings, windows, doors, etc. Calculation formula:

Q1 = (S / R) * Δt,

Where:

  • S - the area of ​​the element;
  • R - thermal resistance;
  • Δt - the difference between the temperature inside and outside.

When determining Δt, the indicator is used for the coldest time of the year.

Thermal resistance is calculated as follows:

R = A / Ct,

Where:

  • BUT - layer thickness, m;
  • Ct - coefficient of thermal conductivity, W / m * K.

For the combined elements of the structure, the resistance of all layers must be summed up.

Thermal conductivity of materials

The coefficient of thermal conductivity of building materials and insulation can be taken from the directory or look in the accompanying documentation for a specific product.

More values ​​of the coefficient of thermal conductivity for the most popular building materials, we have given in the table contained in the next article.

Ventilation heat loss

To calculate the indicator, the formula is used:

Q2 = (V * K / 3600) * C * P * Δt,

Where:

  • V - volume of the room, cub. m;
  • K - air exchange rate;
  • C - specific heat of air, J / kg * K;
  • P - air density at normal room temperature - 20 ° С.

The air exchange rate of most rooms is equal to one. The exception is made at home with internal vapor barrier - to maintain a normal microclimate, the air must be updated twice per hour.

Specific heat capacity is a reference. At standard temperature without pressure, the value is 1005 J / kg * K.

Air density

The table shows the dependence of air density on the ambient temperature at atmospheric pressure - 1,0132 bar (1 atm)

Total heat loss

The total amount of heat loss of the room will be equal to: Q = Q1 * 1.1 + Q2. Coefficient 1.1 - an increase in energy consumption by 10% due to air infiltration through cracks, leaks in building structures.

Multiplying the obtained value by 1.2, we obtain the required floor heating power to compensate for heat losses. Using the graph of heat flow versus coolant temperature, you can determine the appropriate pitch and diameter of the pipe.

The dependence of the density of the heat flow

The vertical scale is the average temperature mode of the water circuit, the horizontal one is the indicator of heat energy generation by the heating system per 1 square meter. m

The data are relevant for warm floors on a sand-cement screed with a thickness of 7 mm, the coating material is ceramic tile. For other conditions, an adjustment of the values ​​is necessary taking into account the thermal conductivity of the finishing.

For example, when laying carpet, the value of the coolant temperature should be increased by 4-5 ° C. Each additional centimeter of the screed lowers the heat output by 5-8%.

Final contour length selection

Knowing the step of laying the coils and the covered area is easy to determine the flow of pipes. If the value obtained is greater than the allowable value, then it is necessary to equip several contours.

Optimally, if the loops have the same length - do not adjust and balance anything. However, in practice, more often there is a need to break the heating line to different areas.

Contour distribution

The scatter of contour lengths should remain in the range of 30-40%. Depending on the purpose, the shape of the room can be “played” by loop pitch and pipe diameters

A specific example of the calculation of the heating branch

Suppose you want to determine the parameters of the thermal circuit for a house of 60 square meters.

For the calculation will need the following data and characteristics:

  • the dimensions of the room: height - 2.7 m, length and width - 10 and 6 m, respectively;
  • The house has 5 metal-plastic windows of 2 square meters each. m;
  • external walls - aerated concrete, thickness - 50 cm, Kt = 0.20 W / mK;
  • additional wall insulation - foam foam 5 cm, Kt = 0.041 W / mK;
  • ceiling material - reinforced concrete plate, thickness - 20 cm, Kt = 1.69 W / mK;
  • attic insulation - expanded polystyrene plates 5 cm thick;
  • the dimensions of the entrance door are 0.9 * 2.05 m, thermal insulation is polyurethane foam, a layer is 10 cm, CT = 0.035 W / mK.

Next, we consider a step by step example of the calculation.

Step 1 - calculation of heat loss through structural elements

Thermal resistance of wall materials:

  • aerated concrete: R1 = 0.5 / 0.20 = 2.5 square meters * K / W;
  • expanded polystyrene: R2 = 0.05 / 0.041 = 1.22 m * K / W.

Thermal resistance of the wall as a whole is: 2.5 + 1.22 = 3.57 sq. M. m * K / W. The average temperature in the house is taken as +23 ° C, the minimum outside of 25 ° C with a minus sign. The difference is 48 ° C.

Calculation of the total area of ​​the wall: S1 = 2.7 * 10 * 2 + 2.7 * 6 * 2 = 86.4 sq. M. m. From the resulting figure, it is necessary to take away the size of windows and doors: S2 = 86.4-10-1.85 = 74.55 sq. m. m

Substituting the obtained parameters into the formula, we obtain wall heat loss: Qc = 74.55 / 3.57 * 48 = 1002 W

Heat loss accounting

By analogy, heat costs are calculated through windows, a door and a ceiling. To assess energy losses through the attic, the thermal conductivity of the material of the ceiling and insulation is taken into account.

The final thermal resistance of the ceiling is: 0.2 / 1.69 + 0.05 / 0.041 = 0.118 + 1.22 = 1.338 square meters. m * K / W. Heat losses will be: Qп = 60 / 1,338 * 48 = 2152 W.

To calculate the leakage of heat through the windows, it is necessary to determine the weighted average value of the thermal resistance of materials: double-glazed windows - 0.5 and profile - 0.56 sq. m * K / W, respectively.

Ro = 0.56 * 0.1 + 0.5 * 0.9 = 0.56 m * K / W. Here, 0.1 and 0.9 is the share of each material in the window construction.

Window heat loss: Qо = 10 / 0.56 * 48 = 857 W.

Taking into account the thermal insulation of the door, its thermal resistance will be: Rd = 0.1 / 0.035 = 2.86 square meters. m * K / W. Qd = (0.9 * 2.05) / 2.86 * 48 = 31 W.

Total heat losses through the enclosing elements are: 1002 + 2152 + 857 + 31 = 4042 W. The result should be increased by 10%: 4042 * 1.1 = 4446 watts.

Step 2 - heat to heat + total heat loss

First, we calculate the heat consumption for heating the incoming air. Volume of premises: 2.7 * 10 * 6 = 162 cu. m. Accordingly, the ventilation heat losses will be: (162 * 1/3600) * 1005 * 1.19 * 48 = 2583 W.

According to the parameters of the room, the total thermal costs will be: Q = 4446 + 2583 = 7029 watts.

Step 3 - the required power of the thermal circuit

We calculate the optimal power of the circuit required to compensate for heat losses: N = 1.2 * 7029 = 8435 W.

Further: q = N / S = 8435/60 = 141 W / sq.m.

Heat flux density

Based on the required performance of the heating system and the active area of ​​the room, it is possible to determine the heat flux density per 1 square meter. m

Step 4 - determination of the laying step and the length of the contour

The resulting value is compared with the dependency graph. If the temperature of the coolant in the system is 40 ° C, then a circuit with the following parameters will fit: pitch - 100 mm, diameter - 20 mm.

If water circulates to 50 ° C circulates in the line, the interval between the branches can be increased to 15 cm and a pipe with a cross section of 16 mm can be used.

We count the length of the contour: L = 60 / 0.15 * 1.1 = 440 m.

Separately, it is necessary to consider the distance from the collectors to the heating system.

As can be seen from the calculations, for the arrangement of the water floor will have to do at least four heating loops. And how to properly lay and fix the pipes, as well as other secrets of installation, we reviewed here.

Conclusions and useful video on the topic

Visual video reviews will help to make a preliminary calculation of the length and pitch of the thermal circuit.

Selection of the most effective distance between the branches of the floor heating system:

A guide on how to find out the length of the loop of a heated floor:

The method of calculation can not be called simple. At the same time, there are many factors that affect the parameters of the circuit. If the water floor is planned to be used as the only source of heat, then this work is better to be entrusted to professionals - mistakes at the planning stage can be costly.

Calculate the required length of pipes for floor heating and their optimal diameter yourself? Maybe you have questions that we have not touched on in this material? Ask them to our experts in the comments block.

If you specialize in calculating pipes for arranging underfloor heating and you have something to add to the above material, please write your remarks below under the article.

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