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# How long should the underfloor heating circuit be

## How to place your heating pipes

A water underfloor heating system consists of many elements, the main one being the pipes that let heat beneath the floor of the entire house.

Based on how the handyman is more comfortable, you can arrange the communications in 4 ways:

The location of the pipes in a warm water floor pie will have a significant impact on the calculation of the necessary water for heating, but all types are equally effective when properly implemented.

## The power of the system

In order to determine the length of the water floor, you need to calculate how much power the system requires to heat the usable area. To do this, there are special calculators, which include programs for calculations. Specialists have derived tables. They indicate the norms of heating rooms with different heat loss.

Depending on these indicators set the floor line of a certain power. For 10 m2 of the required 1 kW of energy. How to calculate the pipe for underfloor heating?

• For creation of normal microclimate in living room heating equipment should have 120 W/m2 power. The same figure is valid for bedrooms, children’s rooms.
• Balcony and terrace are the cold places with high heat losses, so provide for more power equipment, 150-180 W/m2.
• Rooms on the ground floor and basement level require 130 W/m2.

When calculating the capacity of underfloor heating with a calculator, you enter data on the size of the room, the number of windows, the height of the ceiling, the duration of operation of the building. Floor, wall and roof insulation must be taken into account. The normal temperature in the rooms:

For efficient heating it is necessary to place the water floor in an area of 70%. If the room is 64 m, its area will be 24 m2. 20 % of the room is underneath the stationary furniture. About 19 m2 of the floor will need to be heated. I place the underfloor heating pipes in an area of about 13 m2. If it is necessary to install a water main in the living room, the heating elements will require a power of 1560 watts.

## What is the optimal length for underfloor heating?

Underfloor heating is a great solution for home improvement. The floor temperature depends on the length of the floor heating pipes hidden in the screed. The pipe in the floor is laid with loops. In fact, the number of loops and their length adds up to the total length of the pipe. It is clear that the longer the pipe in the same volume, the warmer the floor. In this article we will talk about the limitations on the length of one contour of the floor heating.

Approximate design specifications for pipes with a diameter of 16 and 20 mm are: 80-100 and 100-120 meters respectively. These data are given for approximate calculations. Let’s take a closer look at the process of installation and pouring of underfloor heating.

## How many pipes do we use?

What to do if the room needs to have a circuit of more than a hundred meters? The solution is obvious: installing more than one loop and a comb is an excellent solution for large rooms.

The main quality of the heating system is its reliability and efficiency. If the calculation showed that we need 140 meters of the contour, but we need to make a system of 2 loops, 70 meters each. In such conditions the equipment in the form of a circulating pump and a boiler heater can qualitatively heat the room, maintain the required pressure and water temperature in the pipes.The circuits do not have to be the same, but you should not make a big difference either. According to the professionals, the difference in length can reach no more than 15 meters.

## Location of pipes

The underfloor heating system includes a considerable list of elements. We are interested in the pipes. It is their length and determines the concept of “maximum length of the warm water floor. They must be laid taking into account the peculiarities of the room.

Based on this, we get four options, known as:

If you make a proper installation, then each of the above types will be effective for heating the room. Different can be (and most likely will be) the meterage of the pipe and the volume of water. On this will depend on the maximum length of the contour of the water underfloor heating for a particular room.

## What is the optimal length of the floor heating pipe?

Underfloor heating is a great solution for improving your home. Floor temperature depends directly on the length of the floor heating pipes hidden in the screed. The pipe in the floor is laid in loops. In fact, from the number of loops and their length and add up the total length of the pipe. It is clear that the longer the pipe in the same volume, the warmer the floor. In this article we will talk about the limitation on the length of one circuit of the floor heating.

Approximate design specifications for pipes with a diameter of 16 and 20 mm are: 80-100 and 100-120 meters respectively. These data are given as approximate calculations. Let’s take a more detailed look at the process of installation and pouring of the floor heating.

### Consequences of exceeding the length

Let’s see what consequences can result from increasing the length of the floor heating pipe. One of the reasons. it increases the hydraulic resistance, which will create additional load on the hydraulic pump as a result of which it can fail or just can not cope with the task assigned to it. The resistance calculation consists of many parameters. Conditions, laying parameters. The material of the pipes used. Here are the three main ones: the length of the loop, the number of bends and the heat load on it.

It is worth noting that the heat load increases as the loop increases. The flow speed and hydraulic resistance also increase. There are restrictions on the flow rate. It should not exceed 0.5 m/s. If we exceed this value various noise effects may occur in the pipe system. Also increases the main parameter, for which this calculation is done. is the hydraulic resistance of our system. There are also restrictions on it. They amount to 30-40 kP per loop.

The next reason is that as the length of the floor heating pipe increases, the pressure on the pipe walls increases, causing this section to lengthen when heated. The pipe in the screed has nowhere to go. And it’s going to taper at its weakest point. Narrowing can cause a blockage of the flow in the heating medium. Pipes made of different materials have different expansion coefficients. For example, polymer pipes have a very high expansion coefficient. All these parameters must be taken into account when installing floor heating.

Therefore pour screed floor heating must be pressurized pipes. It is better to pressurize with air at a pressure of about 4 bar. So when you fill the system with water and start heating it up, the pipe in the screed will be where to expand.

### The optimal length of the pipe

Considering all of the above reasons, taking into account corrections for the linear expansion of the pipe material, we will take the maximum length of the floor heating pipes per circuit as a basis:

## Possibility to connect to one node and pump

The number of loops that can be connected to one collector and one pump is determined by the power of the equipment used, the number of heat loops, the diameter and material of the pipes used, the area of heated rooms, the material of the enclosing structures and many other different indicators.

These calculations should be entrusted to professionals who have knowledge and practical experience in performing such projects.

## Temperature range

The temperature above the floor surface should be a couple of degrees above the comfort temperature of the entire room. Also note that the temperature in bathrooms and corridors must be higher than in living rooms.

Table of temperature above the floor

Room type Temperature, °C
1 Living rooms (bedroom, guest room, children’s room) 29
2 Rooms with frequent stays (office, computer room, game room, kitchen) 30
3 Bathroom, WC 33
4 Corridors, hallways, storage rooms, loggias and verandas 35

The temperature recommended in the table is considered the most favorable for a comfortable stay of people, but these figures can be shifted a little in one direction or another according to your own preferences.

Important: Underfloor heating is a low temperature loop. It should not be heated too much, in which case you will be very uncomfortable to walk on it!

## Underfloor heating calculation

The temperature must be no higher than 55 o C, and in some cases no higher than 45 o C.

precisely: the temperature should be in accordance with the temperature calculated in the project, which takes into account the heat requirements of the particular room and the material of the under-floor cavity.

Use this thermometer to check the temperature, or preferably two.

One thermometer indicates the temperature of the heat transfer fluid in the supply of the underfloor heating (the temperature of the mixed water), and the other one. return temperature.

If the difference between the two thermometers is 5. 10o C means your floor heating is working properly.

What should be the surface temperature of the underfloor heating?

29 o C. In rooms where people are present for long periods of time;

For laying of underfloor heating pipes they use different forms: serpentine, angular serpentine, snail, double serpentine (meander).

It is also possible to combine these forms when laying one contour.

You could, for example, arrange the periphery area in a serpentine pattern and then lay the base area in a snail-shaped pattern.

Which laying is best for underfloor heating??

For large rooms of square, rectangular or circular shape without geometric exclusivity, it is better to use a snail.

For small rooms, complex-shaped rooms or long rooms, use a serpentine sweep.

How big should be the pitch?

The paving pitch should be in accordance with the design calculations.

A pitch of 10 cm is used for the periphery areas. For the remaining zones with a difference of 5 cm. 15 cm, 20 cm, 25 cm. But not more than 30 cm.

This limitation is due to the sensitivity of the human foot. With a larger pipe pitch, the foot begins to feel the difference in temperature of areas of the floor.

How to calculate the length of the pipe?

To do this you can use a very simple formula: L = S / N 1.1, where

S. the area of the room or the circuit for which the pipe length is calculated (m2 ); N. laying pitch; 1.1. 10% pipe reserve for curves.

Do not forget to add the length of the pipe from the manifold to the underfloor heating, including the flow and return pipes.

For example, consider the problem in which you want to calculate the length of the pipe for a room in which the floor has a usable area of 12 m 2. The distance from the collector to the underfloor heating. 7 м. Pipe spacing 15 cm (do not forget to convert to m).

What is the maximum length of a single circuit?

Everything depends on the hydraulic resistance or pressure losses in a particular circuit, which in turn depend directly on both the diameter of the used pipes and the volume of the heat carrier, which is fed through the cross section of these pipes per unit time.

In the case of underfloor heating (if the above factors are not taken into account) you can get the effect of the so-called locked loop. A situation in which no matter how high in pressure you place the pump, circulation through the loop will not be possible.

In practice, it has been found that a pressure loss of 20 kPa or 0.2 bar is just such an effect.

To avoid going into the calculations, here are some recommendations that we use in practice. For 16 mm metal plastic pipe we do not make the contour more than 100 m. We usually stick to 80 m. The same applies to polyethylene pipes. For 18 pipes made of cross-linked polyethylene the maximum length of the circuit is 120 m. In practice we stick to 80. 100 м. For 20 metal plastic pipe the maximum loop length is 120. 125 м.

Can the contours of the floor heating be of different lengths?

The ideal situation is when all loops are the same length. There is no need to balance or adjust anything.

In practice it is possible to achieve this, but more often than not it is not expedient.

For example, at the site there is a group of rooms where you want to make a heated floor. Among them, there is also a bathroom, which has a usable area of floor heating of 4 m 2. Accordingly, the pipeline length of this circuit together with the length of pipes to the collector is only 40 m. Is it really necessary to adjust all the rooms to this length, breaking up the usable area of the remaining rooms by 4 m 2? ?

Certainly not. This is not reasonable. And then why the balancing valve, which is precisely designed to help balance out the pressure loss in the circuits?

Again, you can use the calculations, through which you can see up to what the maximum variation of the lengths of pipes of individual circuits at a particular facility with this equipment.

### UNDERFLOOR HEATING GUIDE AND INSTALL PART 1. Plumbing Tips

But again, without immersing you in complex boring calculations, let’s say that we at our facilities allow a spread of pipe lengths of individual circuits in 30. 40%. Also, if necessary, you can “play” pipe diameters, laying pitch and “cut” the area of large rooms not into small or large, but into medium-sized pieces.

How many circuits can be connected to a single mixer with a single pump?

The physical meaning of this question is similar to the question “How much load can be carried by car??”

What else would you want to know if someone were to ask you this question??

### How to set up & commission underfloor heating systems & manifold flow meters (TUTORIAL)

Absolutely correct. You would ask: “What kind of machine are we talking about??”

So when you ask “How many loops can be connected to a floor heating manifold??”, you need to consider the diameter of the collector and how much coolant is able to pass through a mixing unit per unit time (assumed to be m 3 / hour). Or, also equivalent, what is the heat load of the mixing unit you have selected??

Suppose you have a Valtec Combimix as a mixing unit. What is the heat load it is designed for?? Take its data sheet. Look at the clipping in the data sheet.

Its maximum capacity is 2.38 m3 /h. If we put the pump Grundfos UPS 25 60, then the third speed at a given ratio this unit is able to “pull” the load of 17000 W or 17 kW.

What this means in practice? 17 kW is how many loops?

Let us imagine that we have a house with many (unknown) rooms with 12 m2 of usable floor space in each room. Our pipes are laid with a pitch of 20 cm, which leads to a length of each circuit, taking into account the length of the pipes from the floor heating itself to the collector, 86 m. In accordance with the design calculations, we also obtained that the heat take-off from each m 2 of this floor heating gives 80 W, which leads us accordingly to the heat load of each circuit

How many rooms or similar circuits can our mixing cabinet provide heat?

17000 / 960 = 17,7 such circuits or rooms.

In practice, however, in most cases it is not necessary to calculate the maximum values. So let’s stop at 15.

Valtec itself has a manifold with the maximum number of outputs to this node. 12.

Do I have to make several heating circuits in large rooms??

In large rooms, the design of the floor heating should be divided into smaller areas and make several loops.

This need arises for at least two reasons:

limiting the length of the loop pipe is necessary so as not to get a “locked loop” effect, in which there will be no circulation of heat carrier through it;

The correct operation of the cement filler plate itself, which should not exceed an area of 30 m 2. The ratio of the lengths of its sides should be 1/2 and the length of one of the edges should not exceed 8 m.

How to know how many loops of floor heating are needed for my house?

In order to understand how many loops of underfloor heating will be needed and on this basis to choose a suitable collector with the same number of outlets, you need to start from the area of the rooms themselves, in which this system is planned.

After that, you calculate the usable area of the underfloor heating. How to do this is described in question 12 ‘How to calculate the effective area of an underfloor heating system??”.

Then, use the following method: based on the pitch of the underfloor heating, break down the usable area of the underfloor heating in each room into the following dimensions:

If the floor area in the room is less than the specified dimensions, it does not need to be divided. We recommend reducing these values by 2 m 2. If the length of the pipe connection from the floor heating to the manifold exceeds 15 m. When breaking up the usable floor area in the rooms, try to also achieve that the length of the pipes in these loops is either the same, or the difference between the individual loops does not exceed 30. 40 %. How to find out the length of the pipes in each circuit, read in question 6, “How to calculate the length of a pipe?”.

How to calculate the usable area of the underfloor heating?

To calculate the usable area of the future floor heating, you need to draw a plan of the room where it will be located. It is better to make a plan to scale.

Separate 30 cm from each of the walls of the room. Shade the resulting space. On the floor plan, mark the places where your furniture will be constantly parked: fridge, wall unit, sofa, big closet, etc.д. Shade these areas as well. The white shaded part of the floor plan will be the usable area of the floor heating you’re looking for.

For clarity, let’s calculate the usable area of the dining room with underfloor heating. The dining room has a floor space of 20 m2. 4 m and 5 m length of the walls, respectively. The kitchen will have a kitchen unit, refrigerator and sofa that will be marked on the floor plan. Let’s not forget to provide 30 cm distance from the walls. Let’s shade the occupied areas. See figure below.

And now let’s calculate the usable floor area.

What is the total thickness of the underfloor heating pie?

It all depends on the thickness of insulation as you know all other values.

At the next thickness of insulation you will have these values (the thickness of the finishing coat is not taken into account):

What do you use to calculate your underfloor heating system?

To calculate both radiator heating systems and underfloor heating systems, we use the company’s Audytor CO.

Here’s a screenshot of the underfloor heating pre-calculation module and the layer calculation module.

When you look closely at these screenshots, you can see how serious the proper calculation of underfloor heating is.

You can also see the operation of the program itself, which makes it possible to monitor visually important parameters such as the length of the pipe, pressure loss, temperature on the floor surface, heat escaping uselessly downwards, useful heat flow, etc.д.

How to determine the dimensions of a manifold cabinet to place all the necessary nodes in it?

Figuring out the dimensions of a manifold enclosure is easy. We again suggest using the products of Valtec and their ready-made recommendations presented in the table, provided that you use ready-made assemblies for underfloor heating produced by this manufacturer.

Model Length, mm Depth, mm Height, mm
SHRV1 670 125 494
VFD2 670 125 594
503 670 125 744
454 670 125 894
ШРВ5 670 125 1044
ШРВ6 670 125 1150
VFD7 670 125 1344
651 651 120 453
SHRN2 651 120 553
5 BFH3 651 120 703
VHF4 651 120 853
5 651 120 1003
SHRN7 658 121 1309

Selecting a manifold cabinet

Model SHRN/ShRV Combimix cabinet ball valve

At what height should a manifold cabinet be installed?

On the one hand, it is clear that when installing the manifold box, the height of the future screed and trim must be taken into account to avoid a situation where the box door cannot even be opened.

On the other hand, you need to consider the ease of maintenance and the need for possible replacement of individual elements of the system with the likelihood of disconnecting the pipeline.

The shorter the pipe section, the greater its stiffness and vice versa.

Taking this factor into account, it is possible to make the manifold cabinet rise by 20. 25 cm from clean floor level.

However, we can not forget about a very important design element. If raising the cabinet causes unacceptable disturbance to the design and it is not possible to solve this problem any other way, lower the cabinet to the floor level, but in such a way that it can be opened.

### Author

#### Kerariel

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