what size actuator do i need for my radiator

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Choosing the right actuator for a radiator is not just about attaching it to a valve, but about precisely matching it to the system's hydraulic parameters and the type of regulation. An incorrect size or actuator force can lead to unstable room temperatures, excessive valve wear, or even damage to the entire heating circuit.

The difference between DN and KVS as the basis for calculation

Many owners think it is enough to select actuators based on the thread diameter on the radiator, but the key parameter is the flow capacity of the valve, indicated by the flow coefficient KVS. The actuator must have sufficient pulling force to be able to open or close the valve even at maximum operating pressure in the system, which often ranges from 0.5 to 1.5 bar.

When selecting, it is always important to consider whether it is a small apartment system with low pressure or a larger building with higher hydraulic resistance. If the valve is too narrow (low KVS), a smaller, cheaper actuator will be sufficient, but if the valve is wide and the system has high pressure, a weak actuator will not be able to fully close and will cause heat loss even when turned off.

Pulling force and torque for turning the valve

The technical parameter that determines whether a valve will open is the pulling force of the actuator, given in newtons (N). For standard thermostatic valves on radiators, a force of 10 to 20 N is sufficient, but for full three-way valves or regulating valves with high pressure, you need a power of 40 N or more. A weak actuator at high pressure will cause the valve to "float" and not reach full closing positions.

Important is also the torque, especially for valves with internal sealing or those that are not used for a long time and may be slightly stuck. When selecting a specific model, for example EUROMIX F4 3/4" kvs=6, make sure the manufacturer guarantees sufficient torque for your system pressure, otherwise frequent failures and the need for technician intervention are likely.

For standard home radiators, a standard actuator with a pull of about 15 N is sufficient.
For system valves with pressure above 1 bar, we recommend an actuator with a pull of at least 25 N.
Possible mechanical obstructions or old valves require an extra strong actuator (over 40 N).

Electrical connection and power supply

No less important than the physical size is the electrical dimension, i.e., the power supply of the actuator. Most modern actuators for home heating operate on 230 V AC, which is standard for regular electrical wiring, but there are also models on 24 V DC, which are safer and suitable for low-voltage systems or intelligent control units. Incorrect power supply can lead to immediate motor burnout or the valve not moving at all.

Another critical point is the type of signal – whether the actuator is two-pole (ON/OFF) or three-pole (with position feedback). A simple ON/OFF signal is sufficient for basic thermostats, but for advanced regulation and centralized control, it is better to use an actuator with the ability to provide feedback, allowing you to monitor the valve status in real time more accurately.

Specifications for mixing and regulating valves

For mixing valves used to stabilize temperature in floor heating or boiler circuits, the requirements for the actuator are significantly higher. Here it is not just about opening/closing, but about smooth position adjustment, which requires an actuator with precise step control and sufficient torque to overcome the pressure difference between the inlet and outlet. An example of such a solution is ROTODIVERT DN20, which requires a specific type of actuator with high precision.

For these applications, it is not recommended to use cheap actuators intended only for thermostatic valves. You must ensure that the actuator is compatible with the valve rotation (e.g., 90 degrees or continuous rotation) and has sufficient durability for frequent position changes. An incorrect choice here leads to rapid gear wear and loss of temperature regulation.

Mixing valves require an actuator with the ability for smooth position adjustment.
It is necessary to comply with the direction of rotation and compatibility with the type of valve (e.g., 3-way vs. 2-way).
For large pipes (DN25 and above), an actuator with an external reducer or high torque is often required.

Practical examples from real-life practice

We often see situations where a customer wants to install a powerful actuator on a small EUROMIX residential valve, which is an unnecessary investment and can lead to damage of the plastic parts of the valve. On the contrary, during the reconstruction of older systems with high pressure, we had a case where a weak actuator was not sufficient to overcome the pressure and the valve remained in a half-open position, which caused the room to cool down and wasted energy.

For a standard residential radiator with a valve EUROMIX F4 1" kvs=10, a standard actuator with a force of 15 N and a supply voltage of 230 V is sufficient. However, if you have underfloor heating with long circuits and high hydraulic resistance, we recommend choosing a more robust solution, such as ROTODIVERT DN25 with an appropriate strong actuator, which ensures reliable operation even under extreme conditions.

Hydraulic resistance and system dynamics

The calculation of the required actuator must take into account not only the static pressure, but also the dynamic changes in the system when the pump is started. A rapid change in flow can momentarily create a hydraulic shock, which a weak servomotor cannot compensate for, and the valve may "break" or damage the sealing.

Frequently asked questions

How can I find out if my valve can withstand a given servomotor?

Always check the maximum allowable pressure of the valve and compare it with the pressure in your system; if the pressure is lower than 1 bar, a standard actuator will be sufficient, otherwise look for a model with a higher torque.

Can I use the same actuator for all types of valves?

No, for 2-way valves a simple ON/OFF actuator is sufficient, while for 3-way or control valves you need an actuator with the ability to smoothly regulate the position.

What should I do if the valve gets stuck even with a strong actuator?

The cause may be limescale deposits or corrosion, so it is necessary to first manually release the valve and check the condition of the seals, or replace the valve with a new one, for example model EUROMIX F4 5/4" kvs=10,6.

Conclusion

The choice of the correct servomotor is crucial for the efficient and reliable operation of the entire heating system, with the decisive factor being not only the physical size, but also technical parameters such as force, torque and power supply.

The correct combination of valve and actuator will prevent frequent failures, reduce energy consumption and extend the life of your heating system without unnecessary repair costs.

Do you have a question about this topic?

Not sure or dealing with a specific situation in your home? Write to us - we are happy to help.