Mixing Unit (Manifold) For Underfloor Heating: Device, Diagrams, Installation

Water floor heating is a little more complicated to regulate than its electric counterparts. Two important devices - the mixing unit for the floor heating and the manifold that supplies water evenly to all circuits of the system - perform the regulating functions.

Using them you can obtain the optimal temperature of the heating medium as well as its quantity, i.e. make the work of the heating equipment as efficient as possible. But how to correctly perform the installation of this important node? This is what we will talk about in our article.

We will look in detail the peculiarities of installation of water underfloor heating in the apartment building, and at the same time we will analyze the device and the main functions assigned to the mixing unit.

We have supplemented the article material with colorful photos and thematic videos on the collector assembly and nuances of installation of the mixing unit for the water underfloor heating.

Article content:

  • Functions and construction of the mixing unit
  • The purpose of using a manifold
  • Peculiarities of installing a water floor in a multistory house
    • How to make a water floor in a multistory house?
    • The subtleties of installing a manifold
  • Making a homemade manifold
  • Conclusions and useful videos on the subject

Functions and construction of the mixing unit

This unit is also called a sub-mix module, which corresponds fully to its purpose. It is designed to mix the water coming from the heating boiler with the water coming from the return side of the circuit to obtain a heating medium of an acceptable temperature

The boiler normally heats the water quite strongly, up to 80-90 degrees. For underfloor heating systems, this temperature is quite high, so the coolant needs to be diluted, and the easiest way to do this is with the return flow, which has already cooled.

Such devices are installed in heating systems with two or more working rings if underfloor heating is an additional way to heat simultaneously with radiators, and when the house is heated with underfloor heating only.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

The mixing unit for the liquid floor heating consists of a number of temperature sensors and a control head in order to supply the circuit with the correct temperature

The main components of the mixing unit are the two way valves with thermostats, the three or four way valve and the circulating pump.

If the boiler is already equipped with such a pump, then for the underfloor heating you have to buy another device, it will operate separately. The radiators are usually supplied with a temperature of 70-90 degrees, but for the floor heating it has to be cooled down to 35-40 degrees.

This is how the cooled return in a three-way valve system is mixed:

  1. Hot water is supplied from the boiler.
  2. The heating medium passes the three-way valve and enters the circuit leading to the floor heating manifold.
  3. The temperature sensor registers the temperature of the fluid.
  4. If the temperature is higher than normal, the three-way valve is triggered.
  5. It opens and the heating fluid mixes with the cold return flow.
  6. When the temperature of the heating fluid drops to the set temperature, the valve closes.

The two-way valve shuts off the flow of the heating medium until the circulating water has cooled down to the required temperature level.

Four-way valves for underfloor heating are divided into two varieties: X-shaped, working on the principle of two way cocks, and rotary valves that allow the mixing of the hot heating medium with the return in perfectly accurate proportions.

In addition to the pump and valve, the installation and use of the mixing unit requires a temperature sensor as well as a thermostat that will switch off the pump if the water temperature is too high.

Often the mixing unit is sold together with a manifold, but if it is not included, the necessary elements must be purchased and correctly installed.

Image gallery


Floor heating mixer

Technical fittings manifold with manifold

Triple acting rod mixer before the pump

Floor heating mixers in systems floor heating systems

Four-way stem mixer

Flow mixer unit with servo motor valve

Position of the unit next to the manifold

Factory assembled mixing unit

The following order should be observed: Put the three-way valve first, then the circulation pump, and connect the manifold after it. With this arrangement the pump will feed the heating medium through the valve. If the pump is placed before the valve, the latter will simply not work, as the flow will simply be misdirected.

The pipe through which the coolant enters must be fitted with a check valve to prevent cold water from flowing back into the system.

A further useful element that will ensure the normal operation of the mixing unit in systems with a two-way valve is the bypass. If all openings on the manifold are closed, the heating medium will flow through the bypass and circulate in a closed circuit until it cools.

In heating systems with two-way valves, the bypass is a must. In systems with three- and four-way valves you can do without it. However, in combination with a three-way valve the bypass enables both quantity and quality control of the heating medium.

In addition to the bypass, a balancing valve must be included in a two-way valve system with which the volume of the heating medium flowing through the bypass is regulated. This device is needed to control the cold water portions mixed with the hot water.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

The three-way mixing device for the water floor heating is designed to control the temperature of the heat carrier by mixing the cold and hot water flows

A set of devices, called a mixing unit, can be purchased as a complete set in the store. But, according to experienced craftsmen, buying individual units will be more reliable and cheaper. Systems with two-way valves and thermostats are suitable for compact circuits with small boilers.

Selecting a three- or four-way valve, you should consider its capacity and the size of the area the system serves.

On small areas, a device that passes about 2 cubic meters of coolant per hour will be sufficient. But if the area in question is over 50 square meters, it is better to take a mixing valve with a capacity of 4 cubic meters per hour.

There is an adjustment cap on top, with which you can set the temperature of the coolant. It is not always necessary to adjust the temperature because the manufacturer usually sets it at an acceptable level.

High performance models of three-way valves come not only with caps, but also with servo actuators. But when connecting the mixing unit, the features of the radiator heating system must always be taken into account.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

When connecting the water floor heating mixing unit simultaneously with a one-pipe radiator heating system, the bypass must always be left open

The bypass is an essential element when the mixing unit is installed. Experts recommend installing a bypass valve on it. This is necessary so that in case of excessive pressure in the system a part of the coolant is redirected to the return.

The important condition for a one-pipe heating system is that the bypass must remain open so that the circuit is always supplied with coolant flow. In two-pipe systems, on the other hand, the bypass must be closed.

If the water floor serves as the main heating method, a mixing unit can be dispensed with if desired.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

If the water floor heating is installed as auxiliary heating in a two-pipe radiator system, the bypass must be closed

In this case the temperature controller for the water entering the circuit is a thermostat. In this case, the heat transfer medium heated to 70-90 degrees will flow directly to the underfloor heating system.

As soon as this hot flow reaches the collector return, a thermostat installed at this point detects the increased temperature and stops the circulation of the heating medium. When the water cools to a predetermined temperature, for example to 40 degrees, the thermostat is triggered and circulation resumes.

This option has a significant drawback - not all flooring easily tolerates heating to 80 degrees. Neither for parquet nor for linoleum this heating mode can not be used, but for ceramic tiles it is quite acceptable option.

Another case, when the mixing unit is not necessary, is when the heat transfer fluid is heated by the heat pump, as the water temperature is unlikely to exceed 40 degrees. By the way, the heat pump can be made with your own hands, significantly saving on the purchase of expensive equipment.

The purpose of using a manifold

The manifold is a device by means of which the heat transfer fluid flow is distributed to the individual water floor circuits and then returned back for heating. The collector unit looks like two pipes with holes to which the system circuits are connected.

The presence of a distribution collector in the floor heating scheme makes it possible to control the volume of the coolant flow. One of the pipes of the collector is the supply pipe, the hot water flows into it and the inputs of the water floor circuits are connected to it.

The return pipe of the circuits is connected to the return pipe of the collector. The holes to which this connection is made are usually equipped with threaded, fitting or other connections.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

The collector consists of a number of elements such as the collector itself (1 and 2); the adapter for the Maevsky tap (3); the drain cock (4); the air vent (5); the valve (6); the bracket (7); the Eurocone (8)

The various devices by which the coolant flow rates can be adjusted are installed here. The simplest version of an industrial manifold is a pipe with a connector, which is called a eurocone. It is quite a convenient and reliable unit, but it does not allow controlling the water flow.

To use such a device effectively, it is necessary to additionally purchase and install a number of elements.

The collector manufactured in North Korea is slightly more complicated. In addition to the connections on the outlets there are valve valves, no automatic flow control is provided. This is an excellent and inexpensive option for a water floor in a small area with two or three circuits of equal length.

This system does not require complex control. But in large areas this type of collector will have to be supplemented with automation.

In addition, the axial distance between the supply and return sections in Chinese devices does not meet the standards adopted in Europe, which may cause problems when connecting it to devices manufactured in Europe.

Ball valves in such devices are sensitive to poor quality water, with time they start to leak. To fix the problem it is sufficient to replace the sealing rings, but it is worth considering that such repairs will be necessary from time to time.

If the water floor system is to be automated, it makes sense to buy at least a manifold with control valves.

Such valves can be fitted with servo drives connected to the thermostats in the rooms. This will provide automatic control of the heating medium flow according to the air temperature in a particular room.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

For the automatic operation of the hot water floor heating system the flow meters (marked with a frame) are installed in the manifold input side and the servo connectors (blue caps below)

The hardest thing to control is a water floor system where the individual circuits differ markedly in length but this is generally the case in complex systems. In such a situation the best choice is a manifold with flow meters in the flow and sockets in the return for the installation of actuators.

From the flow meters it is possible to adjust the flow rate of the heating medium and the actuators in combination with the thermostats allow the setting of a suitable temperature on each circuit.

If there is no need for automatic control, a supply manifold with flow meters and a return manifold with conventional valve cocks can be purchased.

There are times when it is not possible to select a manifold with the number of connection sockets that corresponds to the project. Then it is possible to take a device \"with reserve\". And extra holes are simply closed with plugs.

This solution may be useful if you later need to add a couple more loops to the water floor system.

Peculiarities of installation of water floor systems in multi-storey buildings

It is thought that the construction of water floor systems in high-rise buildings is impossible, but this is not entirely true. In practice, such a project can be implemented, but requires agreement with the provider of central heating services. They can only be installed on the first floors of buildings.

How to make a water floor in a multi-storey house?

There are two options: complete replacement of the radiator system with a water floor or installation of an additional heating system along with the operation of radiators.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

The optimum place for a hot water floor heating system in an apartment building is where the return of the common riser pipe connects to the boiler house tap

In the first case, the flow of heat carrier in the new system must be carefully calculated, as it must match the previous volumes. It is not necessary to reconstruct all heating in the apartment, you can limit yourself to one room.

If the water floor plays the role of auxiliary heating, heat meters will be needed. In addition, it is necessary to clarify whether the central heating system can cover the increased capacity and flow of the coolant.

If a high-rise house has a radiator system with upper distribution, the connection of the water floor is best made at the connection of the common riser return with the pipe leading to the boiler room. It is necessary to install filters in front of the water floor.

This is necessary due to the low quality of the heat carrier in the domestic centralized systems, otherwise the floor heating circuit will very soon get clogged.

Filters should be cleaned regularly. They are more than relevant for a direct connection to the central heating system, but the use of a heat exchanger helps to make the problem of blockages less acute and the operation of the water floor more stable.

But this requires the installation of an expansion vessel, heat exchanger, safety group and filter.

Tips of mounting a manifold

The flow side of the device must be mounted above the return side when mounting a water floor manifold. It is also possible to do the opposite, but it does not make much sense.

The manifold will work, just with the upper return part of the heat from the supply part will be transferred to the return flow, i.e. the heat energy is simply lost.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

It is very important when assembling and installing a water floor collector unit to connect all the elements of this device in the right order, for example using this diagram

The installation of flow meters is an important issue. They should be mounted on the flow side, they are useless on the return side.

In addition to the manifolds, flow meters and actuators with temperature sensors, a drain cock is needed for the installation, as well as a Meuse valve with adaptor, pipe fittings for the water floor, shut-off valve, etc. etc.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

In contrast to underfloor heating manifolds, the flow meters are always installed in the supply area, and the return area is equipped with actuators with thermoregulators

A manifold box is used to install all these devices. It is a metal box with doors, inside there are adjustable rails. Such a device makes installation much easier, but is not cheap.

So if there is a niche of suitable dimensions around the installation site, you can use it.

If the collector is mounted without a special cabinet, it must be suspended on brackets. As far as the collector location is concerned the rule applies: the higher the better, i.e. the collector should be mounted at the highest point of the system.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

The collector cabinet is a very convenient device that facilitates installation of the water floor heating system. But if there is a desire to save money, it can be replaced by a recess in the wall

This is due to the need to remove air from the system, for which a Maevsky valve is installed at the top of the manifold. In addition, it is best to install the manifold at an equal distance from all rooms, i.e. close to the center of the system so that the lengths of the individual circuits differ as little as possible.

Only nine individual floor heating rings can usually be connected to a single manifold. If the heating system is too complex and more than nine circuits need to be installed, two or more collectors are required.

In a multi-storey house it is not always possible to place the collector at the top. Then it is possible to place it below, even in the basement. But the problem of removing excess air from the system has to be solved differently.

The Maevsky valve on the collector itself will be useless. The venting device together with the shut-off valve installed before it has to be installed on the return of each circuit.

The installation is carried out in the area between the pipe and the collector, the Meyevsky valve must be easily accessible.

That way, if the collector is installed too low, instead of one Meyevsky valve as many air vents as the number of circuits will be stacked. Plus the same number of shut-off valves.

The manifold is assembled as follows:

  1. Install a manifold cabinet or prepare a special niche.
  2. Assemble the manifold, install additional modules: servo drives, flow meters, etc.
  3. Connect the manifold supply to the pipe leading from the boiler.
  4. Install a shut-off valve on the manifold return.
  5. Installation of manifold in cupboard/bay.
  6. Pipe connection to supply and return.
  7. Installation of mixing unit.
  8. Check installation quality, remedy faults.

Utually the manifold installation starts before the pipe laying and screed casting, therefore the floor level will rise noticeably at the end of work. The manifold cabinet already takes this moment into account.

But when installation is carried out with brackets, the unit should be placed about one metre from the subfloor.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

Do not install the floor heating water manifold too low, the lack of space may cause problems when connecting the pipes to the connectors

It is not necessary to hang the manifold too low, this position may make the pipe connection difficult. The connection to the polypropylene pipes that lead from the boiler is made with a connector that has a nut for the collector thread and a coupling for polypropylene pipes.

The air vent should be installed at the top point of the collector, and its head will point upwards. But the heads of items such as flow meters and actuators will point down when properly installed.

Usually the threads on the manifold are three-quarters of an inch, and the Maevsky cocks have half-inch threads, so an adapter must be used. The material of the adapter must match the material of the manifold.

There are two threads on the manifold return connection, one for connection to the heating boiler and one for installation of a shut-off valve.

All threaded connections need a seal, which can be realized by means of a sealing ring or, if such a ring is missing, by wrapping with hemp, linen thread, FUM tape, etc.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

When assembling the mixing unit for the floor heating water, all threaded joints must be carefully sealed using FUM tape or other materials

When connecting the metal plastic pipe to the manifold connector, the pipe edge must be flared and scraped. This will save the seals from accidental damage.

After this, the union nut should be put on the pipe, then the crimp washer, carefully attach the pipe to the connector, hand-tighten the nut, then carefully tighten with an adjustable wrench.

A mixer unit should be installed before or after the manifold. If, for some reason, this is not possible, a bypass with shut-off valve is installed instead.

The mixing unit is usually fixed with cap nuts. Such elements require the obligatory use of rubber gaskets.

Making a homemade manifold

To make a manifold from polypropylene pipes, we recommend using 32 mm or 25 mm designs, corresponding tees and stop valves.

How many floor heating loops will be connected, so many tees and valves are needed for the manifold. It will also be necessary to buy a circulation pump and a valve for the mixing unit.

Mixing unit (manifold) for underfloor heating: device, diagrams, installation

If the water floor heating system does not need serious automatic regulation, you can make a manifold yourself or buy a simple model with ordinary shut-off valves

To solder pipes, a special soldering iron is needed, and at least minimal experience with such equipment. Tees and pipes are used to form the supply and return sections of the manifold. The pipe sections should be very short so that the tees are separated by very little space.

After that, stopcocks are soldered, as well as fittings for the connection to the pump, etc. Such a simple device will be inexpensive if no flow meters and other controls are installed.

But a more advanced plastic manifold is easier to buy than to make, the cost of such a device is not great.

Conclusions and useful video on the topic

Interesting material on the assembly and installation of the mixing unit:

The video demonstrates the process of assembling a set of manifold elements:

An inexpensive manifold making itself is explained in this video:

The distribution as and the mixing units are very important elements for the water floor. You can do without them only if the system includes only one or two circuits and occupies a small area.

But if you decide to create a quality water floor, then all these nodes must be assembled and installed correctly so that the system works with maximum efficiency and minimum costs.

You are engaged in installation of water floors not the first year and are familiar in practice with all the subtleties of this process? Share your experiences in the comments to the article - this information will be extremely useful for beginners.

Are you finding mistakes or material in the article not corresponding to theoretical norms? Please tell us about it in the comments block.

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