Thermostatic valve for a radiator: purpose, types, principle of operation + installation

Alexey Dedyulin
Checked by a specialist: Alexey Dedyulin
Author: Oleg Sysoev
Last update: May 2019

A standard heating system cannot be called flexible. To adjust the parameters of the battery, invented various devices.

One such device is a thermostatic valve for heating radiators. It is used to regulate the heat transfer of the system depending on weather conditions. In this article, we will analyze the device and the principle of operation of a thermal valve, get acquainted with existing varieties and major manufacturers.

We also give installation recommendations, providing the material with visual photos and video reviews on the installation and the response speed of devices of various brands.

Why do I need a thermostatic valve?

The valve solves two problems: it maintains a room temperature at a comfortable level plus saves energy.

But in order for him to really cope with such functions, you need to understand in which cases the device is appropriate and how to install it correctly.

If in the middle of winter there is a need to open windows so that the temperature in the room drops to an acceptable level, the thermostat is definitely needed. But it will not help when the batteries are barely warm - it may become even colder with it.

In the second case, it is better to try otherwise to adjust the temperature in the room: change the volume of coolant in each radiator, adjust the operation of the boiler (for a large area), select optimal circulation pump or adjust the work of an existing one.

Conventional thermostatic valve
The price of the thermostat varies in the range of several hundred rubles (200-600), so re-equipment of the heating system will cost inexpensively. But there are also expensive models

As a temporary measure, control fittings can be used. But ball valves are not recommended for this purpose.

Device and features of the device

Consider how the thermostatic valve works and by what principle.

How is a thermal valve arranged?

The device consists of two main working elements - a valve and thermostatic head. The first is most often made of brass, sometimes nickel-plated, its lower part blocks the pipe, and the top continues the pressure rod and spring.

Valves can be bronze (nickel or chrome plated), as well as stainless steel. The latter are rare and expensive.

What happens inside the valve? A sensing element is present in the head device. It is located in a cavity with gas or liquid (bellows).

Heating provokes expansion in this medium, the element is pushed forward, presses on the rod, spring, and later on the valve. The force of pressure determines the degree of overlap.

Thermostatic valve device
The figure shows a device with liquid in a bellows. Gas thermostats respond faster to temperature changes (5-10 minutes), but also cost more. There is no special difference from this during operation

An additional part of the thermostat is a plug or a handle with a scale. Some devices have electronic controls.

The principle of operation of the device

Let's take a closer look at the principle of operation of thermostatic valves for batteries. The mechanics of their action looks like this: when the temperature of the coolant or the environment changes, a gas or liquid in the head reacts to these vibrations.

The sensing element acts on the pressure rod, and he goes up or down. When the rod moves down the valve blocks the flow of coolant, which stops the flow of heat, slows down the speed of circulation. The battery does not receive heat, so the temperature in the room does not increase.

And here it is important to distinguish the thermostatic valve from the control valve. The latter can reduce the valve capacity and so regulate the temperature of the batteries.

How the thermostatic valve works
When turning the regulator or entering a digital value on the panel, the user sets the initial value of the pressure in the thermal head, under which it “adjusts” during operation
Radiator Control Valve
The control valve does not have a thermal head. The thermostat is open or closed, it is controlled by a thermal head, it does not change the volume of the coolant, but only turns on and off its flow

Let us examine the principle of operation of a thermal valve using an example. So, set the device to a recommended temperature of 20 degrees. Usually this is the three or the largest point on the scale of the regulator.

What is going on inside the device? If the surrounding air heats the head to 21 degrees, i.e., increases the set temperature by 1 degree, it presses the rod, the flow of coolant into the battery is completely blocked by the valve.

The radiator does not heat up, the room temperature begins to decrease. When the ambient temperature drops to 19 degrees, the thermal valve opens, the battery starts to heat up.

We deal with the types of devices

According to the method of adjustment, the valves are divided into mechanical and automatic. The former require manual rotation of the duct narrowing mechanism in the pipes.

Automatic and manual thermostat
Both devices perform the same function - they adjust the flow of coolant to the radiator in accordance with the parameters set by the user, but the use of automation is less troublesome

Automatic models do not need manual adjustment. When the temperature around the thermostat decreases, they independently fix it and adjust the flow of coolant.

Manufacturers offer different designs of thermostats:

  • Conventional for two-pipe systems - the simplest device. If you need hydraulic linking of radiators in one branch, it is recommended to add a shut-off and control valve on the feed (return) to the circuit.
  • With concealed and open hydraulic superstructure - in such devices there is a coupling with an internal stem, so hydraulic adjustment is possible.
  • For single pipe gravity systems - due to the increased passage, the throughput of these devices is increased to 5.1 m3/ hour, so they can be installed in non-pressure systems.
  • 3-way for bypass circuits - are able to regulate and distribute the coolant in conjunction with bypass. When the set temperature reaches the valve, the coolant is sent to the bypass; when it drops, the bypass partially overlaps.

The percentage of thermal valves for double tubes is much larger than for single tubes, and the latter in our country is about 80%.

This is due to the fact that the device was originally invented for the former, where the coolant is distributed over the devices forcibly under high pressure. Presetting by valves is intended for uniform distribution of pressure throughout the system.

Only some manufacturers have valves for single tubes - Heiz, Danfoss, Heimeier, Oventrop.

In schemes with a single pipe, you can not use the usual "two-pipe" thermostats: they have lower throughput, they are able to work only with a large difference in supply and return pressures, so there will be a risk of redirecting the coolant to bypass.

Externally, the “single pipe” valves are larger in size.

3-way thermostatic valve
Three-way valves are appropriate in schemes with a solid fuel boiler, as well as for separation of flows, bypass piping of radiators. The device can also be used in single pipe wiring

Thermostatic valves also vary in shape. They are straight, angular or come in headsets with jumpers for pipes. Direct are appropriate on conventional batteries. Corners are needed in schemes with a lower pipe connection, when the CO is partially masked under the floor.

A separate type of thermal valves is electronic. They have wider functionality than usual. With their help, you can set different temperatures in the room for every day of the week and even hourly.

Electronic thermostatic valve
Electronic thermal heads are more expensive and more common than usual: inside the case there is a compartment for two batteries. There are models with removable and integrated control units

Electronic thermostats provide significant savings in coolant flow. If from 8 am to 6 pm there is no one in the apartment or house, the device will regularly maintain the minimum temperature. And by the arrival of the owners heats the room to a comfortable level.

On sale there are valves with an anti-vandal casing. They are reliably protected from unskilled interference and are suitable for installation both in a house with young children, and in kindergartens, schools.

Features of installation and connection of the valve

The device itself is simple, but special attention must be paid to installing and calibrating the thermostatic valve on radiators. Proper installation will ensure the accuracy of the device.

What factors are considered during installation? A variation of the thermal valve is for single tube or double tube. Plus the direction of movement of the coolant - it comes from below or above.

The direction of movement of the coolant on the valve
On the valve itself, the direction of movement of the coolant is indicated by an arrow. According to this marker, it is necessary to install thermostats on radiators, otherwise the device will not work correctly

Hot water pipes to the battery are supplied in different ways. It depends on the heating circuit. Placements for plugs and thermostats are also different. The general recommendation for most thermostat models is to place them within 40-60 cm from the floor.

The installation algorithm is approximately as follows:

  1. We disconnect the radiator from the heating system and lower the water.
  2. We remove the section of the horizontal pipe and the crane, too.
  3. The thermostat can also be mounted in the radiator cap if a shut-off valve is installed in front of it. Or make an insert in the horizontal part of the pipe in front of the battery.
  4. The tightness of the joints is important. We provide it with standard winding of the FUM tape on the threaded section.

The traditional connection scheme is as follows: bypass -ball valve - temperature regulator.

Another point: there are such systems where in different rooms the coolant moves in different directions. This is especially true for U-shaped risers.

Installation nuances for single pipe and double pipe systems

AT single tube hot water circulates in one pipe with radiators connected in series. The coolant pipe enters the top of the batteries. The latter runs through the installation, leaves the bottom from the same side and goes to the main highway.

One-pipe and two-pipe heating system
A single-pipe system is considered ideal for private construction and an apartment building up to 5 floors. In other cases, it is recommended to equip a two-pipe СО

In a single pipe system, the thermostat is placed on an unregulated bypass. This jumper combines a straight pipe and a return, so hot water moves freely after the pressure is blocked by the valve.

Such a jumper can be welded to the pipe yourself, for which a piece of pipe with a diameter of not more than 8 cm is suitable. In this case, you need to prepare the holes in the appropriate places.

Thermostat installation diagrams
Standard and recommended thermostat installation schemes for single-tube and two-pipe СО. The figure shows how to connect a valve with a jumper (bypass) and a bottom valve

In the two-pipe, the coolant flows to radiator through one pipe, and is discharged through another. No bypass is needed; the thermostatic valve must be installed on the water supply pipe.

Rules for adjusting the operation of the device

After installation, you need to adjust the operation of the device. To do this, first close the windows and doors - isolate the room to prevent heat leakage.

Then we act like this:

  1. We turn on the heating.
  2. We set the valve to the maximum heat transfer position, measure the temperature.
  3. We are waiting for the temperature in the room to rise by 5 degrees and become constant.
  4. Close the valve and wait for a comfortable temperature.
  5. Further on, we slightly open the thermostat until we hear the noise of passing water. The case of the device itself should warm.
  6. The last position you need to remember.

In a private house, air must be vented from the batteries before adjustment. At the same time, maximum care must be taken so that there is no emission of hot steam.

Room temperature adjustment
When more than three batteries are connected to the boiler, each thermostat must be opened at a different level so that the heat is distributed evenly throughout the rooms

Adjustment begins with the coldest room. It needs to be warmed up well to move to other rooms.

Frequent installation errors and possible problems

The first mistake is to position the thermal head vertically. The problem is in the hot metal valve under the head: hot air flows from it upward.

This air heats the head, and it turns off the radiator erroneously. As a result, the battery is almost always turned off, the room does not warm up. The device must be installed horizontally ("head" in the room).

Incorrect thermostat installation
The instructions for the thermostat on the diagrams show how and where to install it in different cases, but there is not a single circuit with a vertical arrangement. If it does not work out vertically, you need to use devices with remote sensors

The second mistake is the location of the thermostat where the temperature differs from the real one in the room. Example: in a niche with a battery. In this embodiment, the head will always be “hot”.

A significant malfunction in its work will be present when curtains are placed behind a dense fabric, under window sills, at the edges of window openings.

If the thermostat cannot be positioned otherwise, the model with the remote sensor will again help out. They differ from conventional devices by the presence of a capillary tube of about 2 meters with a temperature sensor at the end. You can attach a similar device to the wall away from the window and the battery.

Thermostatic valve with remote sensor
Models with a remote element more accurately than conventional devices determine the temperature due to their location at a distance from the radiator, but they also cost much more

On sale there are also heads with external regulators, the installation of which is possible anywhere at a distance of up to 15 m from the battery and valve. There are electronic heads that are controlled by thermal computers.

The thermostatic valve completely shuts off the flow of coolant. If in radiant heating system all devices will do this at the same time, there will be problems with the boiler. A possible solution is bypass valves on the circuits.

If there are 2-3 radiators in the room, does it make sense to put thermostats on each battery? Will there be a conflict between them? In this case, it is necessary to balance the adjustment valves (ball valves).

Conclusions and useful video on the topic

What is a thermal head, why is it needed and how does it work.

Analysis of the finished system with a thermostatic valve.

An experiment on the response speed of thermal heads from 4 manufacturers.

The use of thermal valves for radiators allows you to make the heating system as flexible as possible..

With their help, you can adjust the temperature of individual batteries so as to constantly maintain a comfortable microclimate in the room. But at the same time, it is important to take into account the appropriateness of installing such devices, to correctly install and configure them.

Thinking about installing a thermal valve, but want to clarify a couple of points for installation? Ask your questions under this article - our experts and site visitors using such temperature-control equipment will try to answer you as detailed as possible.

If your heating system is equipped with thermostatic valves, share your opinion with other users. Tell us, what equipment manufacturer did you prefer, is it convenient to use, are you satisfied with the result? Write your recommendations in the comments section, add unique photos of the thermal valve.

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Visitors Comments
  1. Semen

    With a thermostat, life in the apartment becomes much more comfortable, I know for myself. It is unclear how they drown in the boiler room - they do not really adjust to the weather outside. They can continue to drown to the fullest in the thaw, and in the apartment the Sahara just begins. With a thermostat, you can simply reduce the temperature to a comfortable temperature. I generally took myself an electronic one. Yes, more expensive, but the temperature is precisely set and many functions by the clock.

  2. Gregory

    I took and installed a thermal head Giacomini P470 for testing. It is manually adjusted, there are many divisions, the air temperature in the apartment from +8 to +30 goes. I don’t understand how it works.
    Put as in the instructions, horizontally. I touch the battery, it’s hot, then warm, cold doesn’t happen. But the room did not seem to be so hot as before that the window had to be opened. So far I’m thinking whether I need to go to other rooms or not.

    • Expert
      Alexey Dedyulin

      Of course, put in other rooms, the only way you can fully feel all the advantages of a thermal head, when in different rooms you can set a different temperature. And the thermal head works quite simply - set the desired temperature, and it already independently supports it by adjusting the water supply to the radiator depending on the temperature you set.