How to choose the right radiator valve – type, connection and compatibility
How to choose the right radiator valve – type, connection and compatibility
A radiator valve is a small component that is often underestimated during renovations and heating system installations. Customers choose a nice design radiator and have the piping planned, but when it comes to the valve, they stand in front of a shelf full of different shapes, threads and markings and don't know what they actually need. The result? Either they buy the wrong type and have to replace it, or they grab the first one that falls into their hands and then wonder why the radiator doesn't heat evenly, why the head doesn't fit, or why water is dripping from the joint.
This article will guide you through the entire issue from the basics. We will explain what types of valves exist, what the different dimensions and markings mean, how to determine which type fits your radiator and piping, and what to watch out for when it comes to compatibility with a thermostatic head. If you are planning to replace old valves, renovate a bathroom or install new panels, this text is an essential foundation for you.
Why choosing the right valve is important at all
A valve is not just a tap for opening and closing the flow. A modern thermostatic valve actively regulates the amount of hot water flowing through the radiator, thus directly affecting the room temperature. A properly set valve in combination with a thermostatic head can reduce energy consumption by 10 to 20 percent compared to a system where the valves are set rigidly or are not regulated at all.
It is not only about energy efficiency, but also about the hydraulic balance of the entire system. If you have ten radiators in your house and each has a different flow setting, those furthest from the boiler will be cold, while those closest will be overheated. A properly dimensioned and set valve is therefore crucial not only for comfort, but also for the long life of the pump and boiler.
Types of radiator valves – overview and differences
We encounter several basic types on the market. Each has its application and not every type fits into every situation.
Thermostatic valve
A thermostatic valve is now the standard for every new installation and renovation. It has a specially shaped stem (cone), onto which a thermostatic head or actuator is mounted. The valve itself is "dumb" – the regulation is ensured by the head, which reacts to the temperature of the air in the room and thus increases or decreases the flow.
A thermostatic valve is sold either as a one-sided (valve with a fixed flow setting set by the manufacturer or installer during installation), or as a two-position valve. A two-position valve allows you to set the hydraulic resistance – that is, precisely limit the maximum flow through the radiator. This is essential for systems with more than five to six radiators, where the system needs to be hydraulically balanced. A typical representative of this category is, for example, the thermostatic two-position valve – 1/2" x EK corner, which allows flow setting and also serves as a thermostatic valve for mounting a thermostatic head.
Manual (hand) valve
A manual valve does not have a shaped cone for a thermostatic head – it is operated directly by hand or with a key. It is cheaper and suitable where you do not need automatic regulation: for example, in technical rooms, corridors, boiler rooms. It is not recommended for apartments and living spaces, because without automatic regulation you have to adjust the valve manually and energy consumption is higher. More about the differences can be read in the article Thermostatic head vs. manual valve – which is more cost-effective.
Ball valve (drain / service valve)
A ball valve is part of most installations, but it is not a regulating valve in the true sense of the word – it is used to disconnect the radiator from the system during service or replacement. It is usually installed on the return (return end), while the thermostatic valve is on the supply. A ball valve is either fully open or fully closed – it has no intermediate position for regulation.
Regulating valve (without thermostatic function)
There are also purely regulating valves, where the flow is set once during installation and then not changed. These are used more in industrial systems or as part of a hydraulic balancing system. In domestic installations, they are mostly replaced by two-position thermostatic valves.
Corner vs. straight valve – connection geometry is the basis
One of the most common mistakes we see among customers is confusing corner and straight valves. They look similar visually, but their geometry is completely different and they are not interchangeable without modifying the piping.
Corner valve (angled, 90°) has an inlet thread in a direction that forms a right angle with the outlet thread. It is used when the supply of hot water comes from the wall (horizontally) and the radiator is connected from below (vertically). This is the absolute most common case in apartment buildings and single-family homes – the riser runs behind the wall, from which horizontal pipes branch out and supply radiators mounted on the wall.
Straight valve (180°) has both threads in one line. It is used when the piping comes to the radiator directly from the floor. This is typical for underfloor piping or for renovation systems, where the piping runs under the floor.
There is also an axial or side valve, which has a special geometry for side connection of the radiator (when the pipe comes from the side, not from below). This type is used less frequently, mostly in specific layout situations or for renovation valves for older panel radiators with side connections.
A more detailed comparison can be found in the article Corner vs. straight valve – how to determine which type you need, where you will also find a step-by-step guide on how to determine the type of connection directly on an existing radiator without the need for disassembly.
Dimensions and threads – what you need to know before purchasing
Thread markings are another area where mistakes often occur. Many customers either ignore them or misinterpret them. However, it is actually a quite simple system once you understand the basics.
What does 1/2" and 3/4" mean
Radiator valves are most commonly sold with an internal thread of 1/2" (inch) for connecting to the piping and various outputs to the radiator. The marking 1/2" corresponds to the so-called BSP (British Standard Pipe) thread with an outer diameter of the threaded part of approximately 20.9 mm. In domestic installations, 1/2" is the dominant dimension.
The relationship is as follows: a 1/2" valve is mounted on a 1/2" pipe (copper, plastic or steel), which is the diameter most domestic piping systems use. Thicker 3/4" valves are used for more powerful radiators, in manifold systems or in industrial installations.
What does „EK" in the designation mean
The abbreviation EK comes from the German „Eurokegel" – euro cone. It refers to a standardized size of the stem of a thermostatic valve, onto which the thermostatic head is mounted. The Euro cone standard is practically universal among European manufacturers – heads from Danfoss, Oventrop, Heimeier, Herz and others are interchangeable, provided both products (valve and head) meet the EK standard.
This practically means that if you have a valve marked „EK", you can mount a thermostatic head from any reputable manufacturer directly onto it without an adapter. You will appreciate this, for example, when you want to replace only the head (e.g., with a type that has a programmable thermostat), but you want to keep the valve.
More about dimensions and threads can be found in a separate article Dimensions and threads of radiator valves – what do the markings 1/2", 3/4" and EK mean.
Thermostatic head – compatibility and selection
A thermostatic head is an add-on that you mount on the valve. It reacts to the temperature of the air in the room and mechanically (or electronically) controls the valve cone – increasing or decreasing the flow of water through the radiator.
When selecting a head, you should primarily consider:
- Compatibility of the thread/connection – most heads are designed for the EK (Euro cone) standard, but there are also older or non-specific valves where an adapter is needed.
- Temperature adjustment range – standard heads have a range of approximately 6–28 °C (positions 1 to 5 or * to 5). Special types may have an extended range, a setting lock function, or a different scale.
- Head size – depends on local conditions. A larger head has a longer temperature sensor and reacts more slowly but more stably. A smaller one is suitable for tight spaces.
- Material and design – if the radiator is in a visible location, aesthetics may also play a role.
On atria.sk you can find, for example, the large thermostatic head HPW, which is robust, with a clear scale, suitable for standard apartment and home installations. For customers who prefer an aesthetic appearance and color coordination with the interior, the large painted thermostatic head is available – in various color finishes that match modern design radiators.
There are also electronic (programmable) thermostatic heads that allow you to set different temperatures for different times of the day and days of the week. These are compatible with the same EK thread, but require batteries or external power supply.
Regulation kits – the advantage of a complete solution
For customers who do not want to deal with the compatibility of the valve and head separately, regulation kits are an ideal solution. These are packages where the manufacturer has already combined the valve, possibly also the return armature, and the thermostatic head so that they are mutually compatible and form a functional unit.
Regulation kit HPW Set1 includes a thermostatic valve and a thermostatic head – it is suitable for simple installations where you only need regulation on the supply. Regulation kit HPW Set2 is more complete and also includes an armature for the return, making it a complete solution for both ends of the radiator – ideal for new builds or when replacing old installations completely.
The advantage of the set is not only guaranteed compatibility, but also cost savings – manufacturers sell sets at a lower price than individual components purchased separately. For more information on when it is worth buying a set and when it is better to buy individual components, read the article Thermostatic set for radiator – what it contains and when it is worth buying a set.
Compatibility with the radiator – what to pay attention to
The valve must be compatible not only with the pipe, but also with the radiator itself. Radiators are connected either from the bottom (bottom connection), from the side (side connection/side block), or centrally (central connection). Each type of connection requires a different valve or adapter.
Bottom connection (H-block)
Modern panel radiators are usually sold with so-called H-block or an integrated valve section in the bottom part. This block already contains a place for a thermostatic valve, often directly with an EK connector. When replacing such a radiator, it is sufficient to replace only the valve, not the entire block. Note – some brands have proprietary systems and require valves from the same manufacturer.
Side connection
Older (especially cast iron or steel section) radiators have a side connection – that is, four threads, two on each side (top and bottom). With these radiators, the valve is mounted directly into the side thread (G 1" or G 1 1/4"). New thermostatic valves for side connection have a reduction, so they fit into a standard thread, but this must be verified before purchase.
Type of system – single-pipe vs. double-pipe
The older Slovak apartment building stock often has single-pipe heating – one riser, with radiators connected in series. In such a system, it is necessary to use a so-called flow coupling or bypass, otherwise closing the valve on one radiator will shut off the rest of the system. In a double-pipe system (separate supply and return for each radiator), the situation is simpler and the standard valve performs its function without limitations.
If you are unsure what type of system you have, a good help is to look at the riser – if one pipe branches off to each radiator separately and there is also a separate return, it is a double-pipe system. If the radiators are connected in series on one loop, it is a single-pipe system.
Material and valve durability
Most modern radiator valves are made of brass (CuZn – a copper and zinc alloy). Brass is resistant to corrosion, has good mechanical properties and is suitable for standard heating systems with water temperatures up to 90 °C and pressures up to 10 bar – which is more than enough for normal home heating.
Lower quality valves are made of zinc alloy (Zamak). These are lighter and cheaper, but have a shorter lifespan, especially if the water in the system is not properly treated or is acidic. In practice, this is manifested by the valve dripping after a few years of operation – corrosion damages the seal and the seat.
The quality of the seal is another distinguishing feature. Good valves have a seal made of PTFE (teflon) or special rubber resistant to temperatures above 80 °C. Cheap seals made of ordinary rubber harden and crack after a few seasons, leading to water leakage.
Practical scenarios from practice – what commonly happens
Scenario 1: Bathroom renovation, radiator replacement
The customer replaces an old cast iron radiator with a new panel radiator "ladder" (garden type). The old radiator had a side connection G 1", the new one has a bottom connection with an H-block. The customer buys the same corner valve 1/2" as before, but finds out that it does not fit the H-block – the H-block has its own valve connector. Solution: buy a valve intended for the given H-block or find out whether the H-block allows direct connection of a standard 1/2" EK valve.
Scenario 2: Head replacement, valve remains
The customer has a 10-year-old valve from a German manufacturer (Heimeier) and wants to replace the old manual head with a thermostatic one. The valve has an EK thread, so it is compatible with most thermostatic heads on the market including HPW large. The customer simply unscrews the old head (nut with M30x1,5 thread, standard for EK), installs the new one and screws it in – without the need to interfere with the piping.
Scenario 3: Straight vs. corner valve – the customer made a mistake
The customer ordered straight valves because they had them before. However, during the renovation, the direction of the piping was changed – instead of floor piping, the piping now comes from the wall. The straight valve simply does not fit physically – the piping would have to go sideways, not up. The customer had to return the valves and order corner ones. Lesson: always check the direction of the piping to the radiator before purchasing valves.
Scenario 4: Noisy radiator after valve replacement
After replacing the valves on five radiators in a family house, a noise started – hissing and gurgling in the piping. Cause: the new valves were not set (the Kv preset on the two-way valve remained at maximum), which caused hydraulic imbalance in the system. The pump "forced" water through the nearest radiators and the distant ones were cold. Solution: hydraulic balancing – setting the preset Kv on each valve according to the design documentation or measured flows.
Step-by-step valve selection process
To conclude the practical part, we summarize the recommended valve selection process in a clear list:
- 1. Determine the direction of the piping – from the wall (→ corner), from the floor (→ straight), from the side (→ side/axial).
- 2. Determine the pipe size – most commonly 1/2" BSP, less often 3/4". If you don't know, measure the outer diameter of the pipe.
- 3. Check the type of radiator and its connection – H-block, side thread G 1", other. Based on that, choose a valve with the corresponding output thread.
- 4. Decide whether you want thermostatic control – if yes, choose a valve with an EK cone for a thermostatic head.
- 5. Consider a two-way valve – if you have more than 5 radiators or it is a larger system, a two-way valve is a necessity for hydraulic balancing.
- 6. Choose a thermostatic head – check compatibility (EK thread M30x1,5), temperature range, type of control (mechanical vs. electronic).
- 7. Consider buying a regulation set – Set1 or Set2 will ensure compatibility of all components and save you time and money.
The installation process of the valve and head is described in the article Installation of a thermostatic valve on a radiator – step by step, where you will also find a list of required tools and tips for sealing the threads.
Most frequently asked questions (FAQ)
Can I fit any thermostatic head onto any thermostatic valve?
Not always. Most modern valves and heads use the EK (eurocone) standard with an M30x1.5 mm thread – these are mutually compatible without an adapter. Some older or non-standard valves (e.g., Danfoss RA or Oventrop Uni) have their own standard. In such cases, an adapter is needed to convert the cone to EK. Always check the technical data sheet of the valve, where compatibility or the type of cone is specified.
What is the difference between a single-regulation and a double-regulation valve?
A single-regulation thermostatic valve regulates only the flow through the thermostatic head – it opens or closes according to the room temperature. A double-regulation valve also allows you to pre-set the maximum flow (so-called Kv value) using a hidden adjustment screw. This pre-setting is used for hydraulic balancing of the system. For systems with multiple radiators, a double-regulation valve is practically essential – without it, some radiators will overheat while others will remain cold.
Why is water dripping from my valve immediately after fitting a new head?
The most common cause is a damaged valve stem sealing (O-ring), which may have been damaged during the removal of the old head or due to long-term disuse. Another possibility is that the head is not properly pressed in and the thread is not tightened. Check whether the M30x1.5 nut is properly tightened (without excessive force – brass threads are easily stripped). If the dripping continues, it is necessary to replace the valve seal – the procedure is described in the article Common problems with radiator valves – dripping, jammed valve, head not responding.
How can I tell that my old valve is not thermostatic and does not have an EK cone?
An old manual valve has a handle (a knob or wheel) on the stem, which turns and directly controls the cone. It looks different from a thermostatic cone – it does not have a smooth cylindrical head with a groove, but rather a flat grip or a square stem. If you are unsure, remove the handle (usually without a tool) and look at the top of the stem – the EK thermostatic cone has a cylindrical protrusion of about 8–9 mm in diameter. If the stem is of a different shape, you will need an adapter or a new valve.
Do I need to change the valve on the return pipe as well, or is it enough to change it on the supply pipe?
For proper regulation, a thermostatic valve is sufficient on the supply pipe only. A shut-off valve (ball valve or control valve) is installed on the return pipe, which is used to isolate the radiator during service. Some installations also have a control valve on the return pipe for better hydraulic balancing, but for home use this is usually unnecessary. The Set2 regulation kit handles both ends of the radiator at once – a thermostatic valve on the supply and a shut-off valve on the return.
What is the lifespan of a radiator valve and when should it be replaced?
A quality brass valve can last 20 to 30 years with proper maintenance. Signs that it needs to be replaced are dripping that does not stop even after tightening the seal, or a jammed stem that cannot be moved even after applying WD-40. Planned replacement is also recommended during renovation when you are changing the radiator – installing a new valve is cheaper while the system is already shut down, rather than a later separate replacement. More about maintenance can be found in the article Maintenance and service of radiator valves – what I can do myself and when to call a professional.
Conclusion – the right valve is the foundation of a working heating system
Selecting a radiator valve is not a complicated science, but it does require answering a few key questions before purchasing: what is the direction of the pipe connection, what is the pipe size, what type of connection does the radiator have, and whether you want thermostatic regulation. If you answer these questions correctly, your choice will be narrowed down to a few specific products and the risk of buying an unsuitable valve will be minimal.
If you are unsure about any of these parameters, the most reliable approach is to photograph the existing radiator connection (including the direction of the pipe and the existing valve with its dimensions) and consult an experienced salesperson. At atria.sk, complete regulation kits, individual thermostatic valves and heads are available, which are mutually compatible and tested in practice.
Also remember that a properly selected and set valve is not just a matter of comfort – it is a direct investment in the energy efficiency of your household. Every degree you lower the room temperature when it is not in use (e.g., during the day when you are at work) means a real saving on your energy bills. And it is precisely this function that a properly chosen thermostatic valve with a head can reliably provide.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we are happy to help.