How to calculate the length of the pipe for underfloor heating
Today it is difficult to imagine a country house without floor heating. Before you start installing heating, you need to make a calculation of the length of the pipe (calculator), which is used for a warm floor. Almost every country house has its own heat supply system, the owners of such houses independently install a water floor if this is provided by the layout of the premises. Of course, you can also install such floor heating in apartments, but such a process can bring a lot of trouble for both apartment owners and workers. This is due to the fact that it is impossible to bring the floor heating to the heating system, and installing an additional boiler is problematic.
The size and shape of the pipe for a warm floor can be different, therefore, in order to understand how to calculate the warm floor, it is necessary to understand in detail the system and the structure of such a system.
How to calculate heat loss
On the correctness of this calculation, depends on the amount of heat that must be supplied to the room to always be a comfortable temperature. The calculations performed will help determine the capacity of the underfloor heating, as well as help make the right choice of boiler and pump.
To perform such a calculation is very difficult. Have to take into account quite a lot of different criteria:
 Time of year;
 The temperature of the air outside;
 Type of room;
 Number and dimensions of windows;
 Flooring on the floor.
 Wall insulation;
 Where the room is located, downstairs or on the upper floors;
 Alternative heat sources;
 Office equipment;
 Lighting fixtures.
In order to make this calculation easier to perform, we take average values. If the house has double glazing and good insulation, this parameter will be roughly equal to 40 W/m2.
Warm buildings with low thermal insulation permanently lose around 7080 W/m2.
If we take an old house, the heat loss increases sharply and is close to 100 W/m2.
In new cottages, where there is no insulation of the walls, where panoramic windows are installed, the losses may be about 300 W/m2.
Once you have chosen an approximate value for your room, you can begin to calculate the heat loss replenishment.
Maximum loop or loop length of the underfloor heating
The loop length of a surface heating system has certain limitations and depends on the hydraulic resistance. The pressure loss in the system in turn depends on the diameter and flow capacity of the pipe.
For different diameters, in order to minimize losses, the following length restrictions apply:
Metal and polyethylene pipes with a diameter of 16 mm:
Metal plastic pipes and polyethylene pipes with a diameter of 20 mm:
What technical parameters are determined when laying the pipeline
Before installing the floor heating circuit, a thermal calculation is generally carried out that takes into account the optimum room temperature, the heat loss depending on the wall material (thermal conductivity), the temperature parameters of the heat carrier in the system. The data obtained help to calculate the number of pipes for a warm floor, that is, to determine their optimal length and diameter. Before installing underfloor heating, the professional and/or homeowner should decide on a number of factors listed below.
Selection of pipe material
For laying underfloor heating, several types of metal and polymer pipes are optimal, the main requirements for the materials: corrosion resistance, good thermal conductivity, low thermal expansion coefficient and long service life. The following varieties are considered when choosing a piping material for underfloor heating:
Copper. Annealed copper pipes have the highest degree of thermal conductivity and high corrosion resistance, their main disadvantage is the high cost. Also copper pipes are difficult to install, when laying them for bending requires a pipe bender, the connection is usually made by gas welding.
Another disadvantage of copper may be the form of issue of the standard coil length of 50 m is not always enough for a heating circuit without joints under the screed.
Stainless steel. Corrugated piping made of stainless steel has reasonable cost at high thermal conductivity, not bad corrosion resistance and relative ease of installation. Its main disadvantage is high hydraulic resistance to the water flow, due to the ribbed surface of the inner walls, as well as not always acceptable quality of metal in the cheap product, leading to corrosion of the walls and leaks over time.
Crosslinked polyethylene PEX. Crosslinked polyethylene (PE) pipes are the main competitors of metal pipes, they have lower cost and the highest degree of corrosion resistance due to the chemical neutrality of polymers.
The main disadvantages of the pipeline made of crosslinked polyethylene high coefficient of thermal expansion, oxygen permeability and low thermal conductivity is eliminated with one shot. After the addition of the PEXpipe shell of aluminum (metalplastic) dramatically reduces the linear expansion of the material from heat and oxygen permeability, improving the heat transfer of the pipeline mowing line.
PEXpipes without aluminum coating are easy to lay; to connect them to distribution manifolds, one can use compression eurofittings that are easily fixed with an adjustable wrench without the use of special tools (soldering irons, press jaws).
Crosslinked polyethylene PEXpipes are sold in coils up to 200 m long, so that their meterage will always be sufficient for the arrangement of heating circuits of any length.
Heatresistant polyethylene PERT. The thermally modified material has the same physical properties of plasticity and flexibility as the usual polyethylene, it has the same drawbacks as the crosslinked analogue of PEH. The improved PERTpipes with inner aluminum jacket have higher characteristics. The pipeline made of heatresistant PE is also mounted on compression sleeves (with aluminum layer on press sleeves), its length in coils is up to 200 m.
Indoor floor temperature
The surface of the heated floor must not be too cold, at a low temperature is difficult to get enough heat in the room, and stay and move on such a surface will not be comfortable. The opposite situation will lead to overheating of rooms and also to discomfort when using the floor. It is generally accepted that the following temperature values of the flooring:
 for living spaces 29 32 ° C;
 For bathrooms, sanitary units and swimming pools 32. 35 ° C;
 for workshops or workrooms with vigorous physical activity 26 28 ° C;
 in corridors, nonresidential rooms, stairwells, gymnasiums 18 22 °C.
Coolant temperature
Temperature characteristics of the coolant also have a significant impact on the calculation of the pipe for underfloor heating, that is, the higher it is, the shorter the length of the pipeline needed to heat the premises.
In contrast to the radiator batteries on the floors the coolant is supplied in a much smaller temperature range from 40 to 55 ° C. It is found that the optimal temperature difference between supply and return is considered a value of 10 ° C is it adhered to when setting and adjusting the heating system.
Pipeline diameter
For laying underfloor heating, they mostly use polymer pipes with an outer diameter of 16 or 20 mm and different wall thickness.
When implementing the first option, the pipeline is easier to lay, to overlap the contour will need a layer of screed with a thickness of 4 mm less. The main disadvantage of 16 mm mowing line compared to 20 mm is its higher hydraulic resistance, which reduces the efficiency of the system. Therefore it is recommended to lay a 16 mm pipe on the objects of small area, and 20 mm products are used in large rooms with heating circuits of great length.
The maximum length of the heating circuits
The greater the length of the pipeline and the smaller its diameter, the greater is the hydraulic resistance of the heat carrier flowing through the loop, and accordingly a greater power of the circulating pump is required to push it through.
Industry produces mainly circular electric pumps with standardized power parameters, designed for certain loads, that is, if the hydraulic resistance in the mowing line becomes too large, the pump can not push the working environment for its normal passage through the circuit.
Based on practical results, the maximum length of underfloor heating pipes has been established: for 16 mm products it should not exceed 100 m, for 20 mm 120 m.
To avoid possible overloads, for normal operation of the system usually not
lay 16 mm pipeline over 80 m, and 20 mm over 100 m.
Laying type
There are two basic forms of laying sex circuits zigzag (serpentine) and snail (spiral). If we look closely at the first option, its main disadvantage is obvious. the different temperature of the coolant in the initial and more distant from the distribution comb. In addition, when laying a snake pipe will have to bend 180 degrees, which is sometimes unacceptable when using rigid materials (will require the use of a pipe bender), and will also lead to an increase in hydraulic losses.
When laying a snail, you get an absolutely even floor heating, due to the fact that the supply and return branches run side by side and their total temperature is always equal to. That is, at the starting point of the circuit, with the hottest supply, the pipe with the coldest return is located next to it, and this situation is observed throughout the room. Another big advantage of the snail is that it is much easier to lay the floor than the zigzag.
Based on the above features, the scheme of laying zigzag is used in narrow rooms of small area and a short heating circuit, and the volute laying the pipeline in the main rooms of the larger area.
It should be noted that the disadvantage of laying by conventional zigzag is eliminated in the scheme with a double serpentine, where the return passes next to the supply pipe.
Spacing of underfloor heating pipes (laying spacing)
The generally accepted laying pitch is a range of 100 to 300 mm inclusive, and the standard size of its changes is a length of 50 mm. These distances are determined by experiment, that is, if the pipes are located closer to each other, the temperature difference between the supply and return temperatures will be too small and the efficiency of the heating system will fall. With greater distances it is difficult to get the heat transfer needed to achieve a comfortable temperature regime, and the floor surface itself will heat unevenly with noticeable strips of heat. Pitch influences the calculation of the length of the pipe for a warm floor, it is clear, the smaller it is, the longer the pipeline is needed for installation.
Also when laying, lower screed temperatures near walls and window openings to the street are taken into account. Therefore, many experts in the area of the edge zones (1 meter from the outer walls) recommend reducing the laying step by 50 mm from the main distance to ensure the uniformity of floor heating.
Also, to reduce heat loss, it is recommended to lay the pipeline at a distance of at least 150 mm from the walls overlooking the street.
Generally accepted balloon laying in large residential areas 200 mm, small rooms such as small kitchens, bathrooms and sanitary units 150 mm.
Connecting the floor heating to the heating system. options, schemes, knots system. If you read about the consumption of floor heating pipes per 1 m2 table, it might also be interesting to know about the options for connecting floor heating pipes to the heating system, you can read about this m in a separate article on our website.
The method of consolidated calculations of the “warm floor
Water underfloor heating is increasingly being designed in homes in Ukraine, as the main source of heat. Its advantages economy, comfort, freedom in furniture placement. I will try to give a simplified, based on personal experience, the author’s methodology of a few points on how to simplify, but at the same time, the most correct to design and create a system of surface heating, which is called a water underfloor heating with your own hands
Calculation formula for pipe length
Remember! the length of each loop is calculated separately. In one room can be several circuits.
Wk x (Dk / W) W x 2 x (Dk / W) K x 2
 Shk is the width of the room
 Dk. room length
 Y. laying pitch
 К. distance from manifold or manifold cabinet to inlet point
We recommend to add not less than 5% to the obtained result. For simplicity, it can simply be multiplied by 1.05. This is the safety factor. Part of the pipe will go under the fittings, somewhere you can make a mistake. Different bending angles of the pipe can also slightly increase the consumption.
Example of pipe length calculation for floor heating
Let’s take a 20 m2 room with sides of 5×4 meters and a collector distance of 5 m as an example. Let’s assume that we make the distance between the pipes equal to 0.2 m. Get it:
5m x (4m/0.2m) 0.2m x 2 x (4m/3) 5m x 2 = 110.53m
Add 5% reserve to the calculated figure and we have 116.06 m. It is possible to reduce to a lesser extent and buy 116 linear meters of pipe for a warm floor.
Calculation of the length of pipes
To calculate how much pipe you need for a warm water floor, use the following formula:
S / H x 1.1 D x 2 = L
How to design Underfloor Heating by LoopCAD (Manual J method).
The factor of 1.1 in the formula is the necessary 10% margin. Unused scraps, wrongly cut or wrongly metered pieces of pipe left over when laying the floor. To take them into account you need to add these 10%.
The distance between the underfloor heating pipes depends on the diameter of the pipes and the heat requirement. If you want to do the calculation yourself, you can use this table:
We calculate the area of the room: 4 x 3.5 = 14 sq.м.
Substitute the values in the formula and get: 14 / 0.2 x 1.1 2.5 x 2 = 82 linear meters of pipes.
Computer help
How many pipes you need for underfloor heating can help you find out with special programs that will make your work easier.
To calculate the length of the pipes, you will need:
o The level of hydraulic resistance;
o Capacity of boiler, pump and other devices.
Competent project and calculations. the key to a quality system. Of course, a qualified specialist will cope with this work better, but if you do not have extra money, all the work you can do yourself, with the help of computer programs.
Calculation of pipes using formulas
To determine how much pipe you need for underfloor heating, you must first calculate:
 The area of the living room or other room that needs to be heated;
 comfortable temperature conditions in the room;
 The pipes used, differing in the material from which they are made;
 The method of laying pipes;
 the distance between the coils of the floor.
Calculation of the area and temperature of the room
To determine the area on which you need to distribute the pipes, you should use the formula
When calculating the area must take into account that:
 the parameter is calculated taking into account the final finishing of the room. If you make a calculation without taking into account the finish, you can make mistakes that can lead to an incorrect project and unnecessary money spent on the purchase of materials;
Example of calculation of the heated room parameters
How to properly calculate underfloor heating with DDSCAD
 the obtained value must be reduced by the area occupied by largesized furniture, as under heavy furniture can not be laid water floor pipes;
 a distance of at least 20 cm is required from the walls. This distance is required for laying of a damping strip designed to smooth the expansion of the floor screed when heated.
Calculation of the length of the pipe for underfloor heating is also carried out on the basis of the average temperature of the room, which is considered the most comfortable for living.
The most comfortable temperature conditions in different rooms
Selection of pipes
The length of the pipe for underfloor heating depends on the material used for the manufacture of pipes. For the floor can be used:

, Notable for low thermal conductivity and low cost. When making a floor of these pipes, it is necessary to reduce the pitch, which leads to an increase in the number of pipes;
the most expensive pipes for the floor, characterized by high heat dissipation
 corrugated stainless steel pipes. Heat transfer performance is slightly less than copper pipes, but remains at a fairly high level. The use of corrugated pipes helps to increase the distance between the coils of the floor, which leads to a reduction in the amount of material needed. The advantage of this type of pipe is also the flexibility of the material, which affects the strength and durability of the finished structure.
Pipes with high heat output and low cost
Methods of laying the floor pipes
How many meters of pipe you need for a warm floor? The next indicator on which the number of pipes depends is the method of laying.
Underfloor heating pipe and how to calculate how much you need
 serpentine (the form of laying corresponds to an elongated sine wave);
 double serpentine (the pipes are laid in a sinusoidal shape. Each bend consists of two pipes smoothing temperature differences);
 coils (spirals).
The most common ways of laying the floor
Laying materials in the form of a “snake” is optimal for small rooms. This is due to the fact that when using 70 m of pipe temperature difference at the inlet and outlet is approximately 10 ° C, which leads to uneven floor heating.
“Double snakes” or “snail” help to achieve the same floor temperature in the whole area of the room.
When selecting the method of laying the pipes, you should also calculate the number of closed loops. The maximum length of the pipes of the contour of a warm floor is determined by experts and is:
 for pipes made of metal plastic and having a diameter of 16 mm, the length of the contour is 100 m;
 for metalplastic pipes with a diameter of 20 mm, the contour should be 120 m;
 for copper and corrugated pipes. 8090 m.
Determination of the laying pitch
Pitch is the distance between the coils of the pipeline, which is the base of the floor.
Distribution of pipes, taking into account the pitch
 The material used for the manufacture of pipes;
 the zoning of the room. Near outer walls, doors and windows, it is recommended to reduce the distance between coils.
Influence of the loop spacing on the required number of pipes
The consumption of floor heating pipes per 1 m2, depending on the distance between adjacent pipes, is shown in the table below.
Final calculation of quantity of pipes
How to calculate the length of pipes for underfloor heating, based on the considered parameters? To calculate, use the formula:
 L. length of pipes required;
 S. calculated area of the room;
 N. the calculated loop spacing of the coils;
 M. distance from the heating collector to the floor;
 1.1. coefficient determining the stock of pipes for arrangement of turns.
For example, the area of a room (S) in which you want to lay a floor heating is 25m². Large furniture occupied 7 m². It is assumed that the pipes will be laid with a standard pitch of 20 cm. The distance from the boiler to the room is 4 m.
The area to be laid is 25. 7 = 18 m².
Thus, to make the floor according to the given parameters will require 107 m of pipes.