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How to connect a unibox for underfloor heating

How to connect water underfloor heating to an existing heating system

The advantages of underfloor heating (abbreviated. TP) over conventional batteries are well known. Therefore, many owners of apartments and private homes want to make a floor heating circuits, and the coolant supply from the existing radiator system.

Here there is a number of difficulties. you need to install and properly connect the water floor heating to keep the water temperature in the loops between 55-60 °C. But the first task is to make sure that it is technically possible to lay the TP “pie” and connect to the existing mains with the lowest cost.

Multibox for underfloor heating

Multibox is designed for decentralized temperature control in underfloor, plasterboard or combined systems. Compensation for deviations of up to 6° on each side, in case of misalignment during installation.

Cover with concealed fixing bolts. Color: white or chrome. Universal installation on all types of walls, thanks to the variable distance of up to 30 mm between the mounting box and cover plate.

Key features

  • Compensation of deviation up to 6° on each side in case of misalignment during duct assembly
  • Cover with concealed bolt attachment
  • Models come with cover and scale head in white RAL 9016 or chrome
  • Universal installation on all types of walls with a variable distance of up to 30 mm between trunking and cover plate


For underfloor heating systems, warm wall systems, and floor/radiator combinations.


Multibox K: Room temperature control,Presetting (V-exact II),Closing,Ventilation.

Return temperature limitation,Presetting,Closing,Drainage option.

Multibox K-RTL: Room temperature control,

Limitation of return temperature,Pre-setting (V-exact II),Closing,


Valve body DN 15.The installation depth of the mounting box for the unit is only 60 mm.Versatile installation thanks to variable distance of up to 30 mm between box and cover plate.

The decorative cover enables a deviation of up to 6° on each side to be compensated for in the event of a misalignment during installation of the box.


Thermostatic head K: 6 °C. 28 °CReturn temperature limiter RTL: 0 °C. 50 °C


Max. Operating temperature: 90 °C Min. Operating temperature: 2°CFor all Multibox models it must be ensured that the flow temperature in the system is suitable for the design of the underfloor heating system.


Valve body: corrosion-resistant gunmetalST: EPDM Seal: EPDM Bonnet: EPDM Return spring: Stainless steelValve insert: brass, PPStem: Niro steel stem with double O-ring gasket.

External o-ring can be replaced under pressure.ABS and PA plastic parts.

Thermostatic element: Thermostatic head K with fluid filled thermostat. RTL return temperature limiter.

Surface treatment:

All models are equipped with a cover plate and scale head in white RAL 9016 or chrome-plated version.


TAH, flow direction arrow, II marking.


Tube-side connection. G3/4″, with taper, allowing compression fittings to be used to connect to polymer, copper, steel thin-wall or metal-polymer pipe.

Multibox C/E and C/RTL

  • Key Features
  • Closed decorative cover
  • Multibox C/E enables connection of actuators or remote control units
  • Compensation of deviation up to 6° on each side in case of misalignment during duct installation
  • Universal installation on all types of walls thanks to the variable distance of up to 30 mm between the mounting box and a decorative cover

Construction sizes and popular manufacturers

Built-in manifold cabinet has the dimensions shown in the table.

Designation Dimensions Manufacturers Price
SHV-1 670×125×494 Grota 1614.00
ШВ-1 648-711×120-180×450 Wester 1713.00
DV-2 670×124×594 Grota 1789.00
SHV-2 648-711×120-180×550 Wester 1900.00
ØÂ-3 670×125×744 Grota 2108.00
TSB-3 648-711×120-180×700 Wester 2236.00
SHV-4 670×125×894 Grota 2445.00
SHV-4 648-711×120-180×850 Wester 2596.00
SHV-5 670×125×1044 Grota 2963.00
SHV-5 648-711×120-180×1000 Wester 3144.00
SHV-6 670×125×1194 Grota 3207.00
ШВ-6 648-711×120-180×1150 Wester 3403.00
SHV-7 670×125×1344 Grota 3981.00

Outdoor manifold cabinet has the dimensions shown in the table below.

Designation Dimensions Manufacturers Price
SHN-1 651-691×120×454 Grota 1466.00
SHN-1 652-715×118×450 Wester 1523.00
SHN-2 651-691×120×554 Grota 1558.00
SHN-2 652-715×118×550 Wester 1618.00
SHN-3 651-691×120×704 Grota 1846.00
SHN-3 652-715×118×697 Wester 1919.00
SHN-4 651-691×120×854 Grota 2327.00
SHN-4 652-715×118×848 Wester 2325.00
SHN-5 651-691×120×1004 Grota 2507.00
SHN-5 652-715×118×998 Wester 2603.00
SHN-6 651-691×120×1154 Grota 2878.00
CHN-6 652-715×118×1147 Wester 2990.00
SHN-7 651-691×120×1304 Grota 3454.00
Shn-7 652-715×118×1300 Wester 3588.00

After completing the installation of the overhead structure, adjustments and branches, you need to do a test run, heating the system to detect defects or malfunctions. In addition, you should provoke a working pressure in the device by about 25 percent exaggerating the pressure in unconstrained operation, and well consider the tightness of the joints.

The main components of the water underfloor heating

In the design of the water heated floor, there are two main parts. The engineering components of water underfloor heating are:

The underfloor heating distribution unit

The floor heating water distribution system includes:

A manifold group. A set of shutoff valves for each floor heating circuit;

Note: A floor heating circuit is an enclosed pipe laid in the floor in a certain way (according to a diagram).

Circulation pump. It ensures the continuous movement of water, as a coolant, on the water floor heating circuit;

Mixing knot or sub-mix knot. It ensures that the incoming hot water (coolant) stream from the heating source is mixed with the chilled water returned from the floor heating loop.

It is worth noting that the assembly of the distribution node of the floor heating is possible from the individual components. Separately, you buy a collector box (metal box) and it is mounted distribution unit, consisting of a pump-mixing unit and collectors. Alternatively, the purchase of the assembled distribution node of the water floor heating in the manifold cabinet. Approximate

Why in most cases we can not just take, and directly connect the manifold of the underfloor heating to the mains of radiator heating?

Collector floor heating is not connected directly to the radiator heating mains due to the fact that the temperature of the water floor heating circuit differs from the radiator heating system temperature by several tens of degrees. The need to maintain a low temperature in the contour of the water underfloor heating is regulated by the norms of SanPiN. When heating the floor above the maximum allowable temperature, convection currents occur, which raise the dust lying on the floor, which greatly increases the risk of various respiratory and respiratory diseases for everyone living in the house. Also, the constant high temperature of the floor, can not favorably affect the organs of the musculoskeletal system.

Connecting the floor heating to the heating system

Even 10 years ago the heating system was not perceived as a primitive heating system with a constant room temperature.

There were very few heating specialists and they were worth their weight in gold and as a rule changed hands.

To correct the heating system or change the temperature mode in the existing heating is very difficult, without knowledge you can disturb the balance of the whole heating.

But it is necessary to try, and in this article we will try to understand.

A comb for underfloor heating with his hands

Since the distribution comb for underfloor heating in the collection costs a lot of money, there are a couple of ways to save money by making the supply and return manifold with their own hands:

In both cases you need to buy thermostatic valves and other elements according to the chosen control scheme. Tees are connected by threading, and polypropylene fittings. by welding (soldering). The number of connections is quite large, each joint must be made reliably so that later leaks did not occur. When making a polypropylene loop, the heating time should be kept and the parts should be connected as fast as possible.

How to wire underfloor heating & radiator zones. UFH WIRING GUIDE

The main disadvantage of combs for underfloor heating, made their own hands. the complexity of presetting and adjustment without flow meters. The flow rate of the coolant will have to be determined at random, even when the pipe lengths in the circuits are the same, because the heat loss in the rooms is different.

It is very convenient to limit the water flow in the TP loops with the help of rotameters. To reduce the flow you need to turn the adjusting washer, the control box in the bulb will react to changes

Methods of temperature regulation of underfloor heating, RTL regulation and other methods

To make the scheme of the floor heating easier and cheaper help return flow regulators. RTL-cocks. The most famous companies, producing heating equipment, offer consumers their thermostatic RTL-cocks, flow limiters for underfloor heating. What are the peculiarities of such temperature control, we will consider further. Also, how do you usually regulate the temperature of the underfloor heating and what kind of temperature is needed

What the temperature should be

The most comfortable temperature of the floor heating is 28 degrees. The comfortable temperature for long-term use is adjusted individually by preference. But usually it is lower, 22 to 26 degrees, so that the floor covering “becomes invisible”.

In individual rooms that are not constantly present, it is usually a good idea if the temperature is slightly higher, up to 32 degrees. It is a hallway (porch), toilet, bathroom.

To maintain the temperature at a given level two different methods are used.

Ways to maintain the temperature of the underfloor heating

The first method is based on a stable high velocity of the coolant.To keep the temperature of the floor heating stable in it it is necessary to supply a certain amount of thermal energy with the coolant. The thermal fluid is prepared at a given temperature and flows through the circuit in a significant volume.

The volume must be such (the speed of movement must be such), that at the outlet of the circuit the temperature of the liquid did not decrease by more than 10 degrees. Then within the circuit the temperature difference will be insignificant and unnoticeable. For example, the circuit is fed 45 degrees, on the outgoing will be 35 degrees. And the surface temperature can be 28 degrees.

connect, unibox, underfloor, heating

The second way is to supply a liquid of high temperature, but intermittently, in portions. A portion of hot fluid fills the circuit fairly quickly (a few minutes), after which its movement stops.

The fluid cools down and gives energy to the screed. The heat-carrying screed gradually absorbs and dissipates energy without overheating at the location of the socket. As soon as the coolant cools down to the set value, a portion of hot water is fed back into the circuit.

For example, the circuit can be fed a liquid of 75 degrees, and its replacement will be carried out after cooling to 30 degrees. Due to the distribution of heat in a solid screed on the surface of the floor will be maintained at all times about 28 degrees.

Temperature control diagram by the mixing unit

To regulate the temperature by the first method, maintaining a significant rate of fluid flow, you must install a mixing node, in which the water is prepared to a predetermined temperature.

The coolant from the boiler is supplied 65. 80 degrees. To reduce the temperature to the required 40.50 degrees, install a displacement unit, which part of the return from the floor heating with a temperature of 30-35 degrees to the input of the circuit. As a result, the thermostatic head, which regulates the ratio of incoming flows, maintains a predetermined temperature at the inlet, for example, 45 degrees.

Such a scheme is not difficult to assemble yourself, which will be cheaper. The basis. a three-way valve, the stem which is regulated by the thermostatic head. It is advisable to install the control element of the thermal head on another branch. The place of installation of the pump and the three-way valve (flow / return) does not matter. But the pump must be installed in the loop manifold floor heating (downstream three-way valve), otherwise the three-way valve will not work.

By setting the thermostatic head to a certain return temperature, we can set the temperature of the floor heating in a wide range.But in order to get colder circuits, the only thing left is to reduce the speed of the coolant flow in them with the adjustment cocks on the manifold.

Temperature control of underfloor heating with flow limiters

The second method of batching hot water into the floor heating circuits is through RTL thermostatic taps (flow regulators). Mixing unit is not used. the loop is supplied with a high temperature coolant, which is required for the radiator network.

At the return of each circuit, an RTL valve with an RTL thermostatic head is installed, which opens when the liquid cools down to the preset temperature. As soon as the temperature of the fluid passing through rises above the set value (the circuit is filled with hot water), the valve almost completely shuts off its movement until it cools down.

These valves are only installed on the return, in order to react quickly to changes in temperature in the circuits. In fact, RTL taps regulate the flow. the amount per unit time (litre/minute). They work depending on the heat loss of each room (circuits, screed area limited by temperature joints), depending on how quickly the screed cools down.

Design feature of RTL taps and RTL uniboxes

The RTL valve has a brass or copper core, which is in tight contact with the same core of the RTL thermal head being installed, so the temperature is transferred to its working body very quickly.

The RTL thermostatic head only reacts to the temperature of the fluid. If it exceeds a level set by the control, the valve shuts off the flow.

The RTL thermostatic head looks very similar to conventional thermostatic heads that are installed on radiators and that measure the air temperature. That’s why it’s often puzzling. how does the head on the manifold “over the air” regulate the underfloor heating in the bedroom

Unibox RTL is a faucet and thermostatic head combined in one body, which can be separately mounted in the wall so that the top is a single cover with or without the thermostatic head. Their purpose is to control a single heating circuit, for example, if the floor is heated only in the bathroom. Using uniboxes is cost-effective, because it is not necessary to install a mixing unit for only one circuit.

But the design can include not only RTL-head, but also an air thermostatic head, so that at the same time and controls the temperature in a small remote room where the floor heating can be the only heating device.

Where it is beneficial to use RTL flow control in heating systems

The RTL collector design is very compact. There is no pump and mixing unit, and the return manifold itself may be assembled from tees with RTL cocks with heads on the inlets. That’s why this system is practical or indispensable where there’s no space for a large structure. For example, this could be in an apartment.

Also, a return flow regulation system is beneficial if there are only a few circuits or only one circuit. Installing a complete mixing unit with a pump in this case is simply not profitable. Uniboxes are used, as mentioned above.

How RTL regulation is used, what are the limitations

The floor heating circuits simply connect in parallel to the main supply, like a radiator branch or a radiator. The supply of the floor heating loop is carried out by a branch from the supply line. And on the return from the circuit, an RTL tap is installed on the manifold or separately (unibox), which is then connected to the common return.

The number of circuits with backflow control may limit the capacity of the pump in the boiler (in the system).

The next limitation. the heat capacity of the screed. This system is designed to work with a massive concrete screed as a heater, which can dissipate high temperatures from the water portion, without overheating the surface fragments. How to make a screed with heating circuits

A general limitation for the use of backflow control is the length of the circuits. The length of the circuit affects both the fill time / cool down time ratio and the total hydraulic resistance of this branch from the total network. Experience shows that in the case of loops with 16 mm pipe, the RTL regulation system works fine for loops up to 50 meters long. If the circuits were made longer. you need to install a mixing unit and use the first method.

In controversial cases, the use of a 20-th pipe with a lower resistance can help.Thus, for RTL system to regulate the reverse flow of the floor heating screed must be fragmented in advance temperature seams, for a small length of the circuits of 35. 45 m.

Types and examples

The Oventrop range includes about 18 models of uniboxes, which are designed for the correct installation of underfloor heating. The most common type

  • minimum temperature. 2 °С;
  • maximum temperature. 100 ° C ;
  • material. plastic;
  • 10 bar pressure
connect, unibox, underfloor, heating
  • maximum temperature. 100 ° C ;
  • material. plastic;
  • 10 bar
  • maximum pressure drop. 1 bar.



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