Table of contents: Buyer's guide Top 5 KNX power supplies
Every modern home, from detached houses to luxury villas, needs a heating control system. This is handled by a KNX heating actuator, of which there are good and less good examples. We compare the five best KNX heating actuators from ABB, Elsner, Hager, MDT & Theben with buying advice.
Nowadays, heating control with KNX usually involves individual room control in order to achieve a high level of comfort throughout the house or building. It is usually the case that a permanently lower room temperature <20°C is desired in the bedrooms, corridors or fitness room than in the living rooms, lounges or swimming pool with >21°C.
A modern KNX heating actuator, which should actually be called a heating actuator with integrated heating controller, is very often selected as a component without knowing the details and functions in detail. Either because it is recommended to the electrician by a trusted wholesaler or simply because it comes from the same manufacturer as all the other components anyway.
There are basically three types of heating systems that can be found in buildings today:
- as underfloor heating, almost classic as in most cases of new construction
- as wall-mounted radiators or radiator heating where old radiator valves have been replaced
- as electric heating or infrared heating/window heating as is common in bungalows
Each of the 3 variants must be controlled and regulated in a house using a KNX heating actuator. It does not matter how large the house is or whether a combination of the three different variants is required.
In the DIY sector, people often buy according to the “cheapest price”, which is why we are also looking at this topic here. Specifically, it’s about the Best price per heating channel or actuator output. Und gerade in diesem Punkt gibt es sehr große Unterschiede.
The fact that the decision to buy the right KNX heating actuator is anything but trivial is shown by the frequent problems encountered by building owners who have already moved into their new house or villa. Want some examples? It is often too cold in the rooms of a newly built house or it only gets warmer or colder with a long time delay. Or the heating is on full blast, so that the residents have to open the windows in a cold sweat. This is shown by the inquiries we receive.
Or the heating/cooling switchover does not work, even though it is supported by the heat pump. Ultimately, everything depends on the KNX heating actuator and can be traced back to its functions and settings, which are anything but trivial, even if it seems so at first glance. If you want to get to the practical goal quickly, we recommend our “8h click guide to KNX programming” where the topic of KNX heating actuators is also shown in all its settings and facets.
The situation is similar to that of KNX power supply units (Top 5 comparison test) or KNX push-buttons (Top 30 longlist)The selection has to be made wisely and the adaptation requires knowledge of system technology and thermodynamics/thermodynamics. Before all readers drop out here, we want to shed some light on KNX heating actuators.
Curtain up for our top 5 comparison test of KNX heating actuators including buying advice. We have selected the best heating actuators with 6-gang to 12-gang outputs including integrated heating controller of the year 2024 and show their strengths and weaknesses.
Quite clearly: The premier class of KNX heating actuators are those with 12-way outputs. Denn umso mehr Ausgänge ein Heizungsaktor hat, umso weniger Platz wird im Elektroschaltschrank/Elektroverteiler gebraucht und bei der Anzahl der Komponenten gespart. Aber ob das allein ausreicht und kaufentscheidend ist, klären wir in diesem Vergleichstest.
Note: Like our other comparison tests, this article is updated regularly. This top 5 of KNX heating actuators is therefore a snapshot that may change in the coming weeks and months. This also applies to the prices.
Purchasing advice: KNX heating actuators in this article
- ABB VAA/S12.230.2.1 KNX heating actuator 12-fold
- Elsner KNX K8 heating actuator 8-fold
- Hager TXM646R KNX heating actuator 6-gang
- MDT AKH-0800.03 KNX heating actuator 8-fold
- Theben HM 12 T KNX heating actuator 12-fold
What do all KNX heating actuators have in common?
All test candidates in the top 5 environment come from Germany and are therefore “Made in Germany”. With the exception of MDT, ABB, Theben, Hager and Elsner Elektronik can be operated manually at the touch of a button so that the switching functions can be tested before ETS programming.
All KNX heating actuators have a 230 V supply cable (L, N, PE) so that the outlets for the individual actuators can be laid neatly. All KNX heating actuators allow the actuator valves to be selected between “de-energized closed” and “de-energized open”.
Basic functions of all KNX heating actuators
- Integrated bus coupler
- Opening/closing of electric actuators with 230 V or 24 V
- Integrated valve protection program
- Function for heating and cooling (interaction with air/water heat pump)
- Very compact design and wide range of functions
- Operating modes: 2-point control, continuous PWM control, integrated controller
- Integrated temperature controller Modes: comfort, night setback, standby, frost/heat protection
- Emergency operating functions
How many heating actuators for a detached house and villa?
The number of heating circuits to be controlled in a house varies with the living space: While a detached house with 160 square meters can manage with approx. 32 heating circuits, a 650 square meter villa can have up to 100 heating circuits. This also means that more KNX heating actuators need to be planned! More on this under Conception and electrical planning in 2024, where we accompany building owners in the D-A-CH region.
Then you also need to know that, depending on the manufacturer, different numbers of actuators may be connected to a single output of the heating actuator. Yes, exactly. This is because the manufacturers set the output power very differently among the 5 test candidates. While the “more expensive” Elsner KNX K8 allows up to 8 actuators per output (230 volts) according to the specification, the “cheaper” MDT AKH-0800.03 heating actuator only allows 3 actuators per output. This also puts the price difference between the two candidates into perspective.
Costs per actuator/heating channel output
- MDT AKH-0800.03 8gang: 8 outputs for 32 actuators = 4.38 Euro
- Elsner K8 KNX heating actuator: 8 outputs for 64 actuators = 4.50 Euro
- Hager TXM646R: 6 outputs for 24 actuators = 6.50 Euro
- ABB VAA/S12.230.2.1: 12 outputs for 36 actuators = 6.66 Euro
- Theben HM 12T KNX heating actuator: 12 outputs for 36 actuators = 7.33 Euro
Which is better: actuator with 24 volts or 230 volts?
Every underfloor heating system needs suitable actuators to open and close the heating circuits. The latter are nothing more than motors that actuate the heating circuit valve. There are variants on the market for 24 volts and for 230 volts. Which would we recommend and why? In our experience, the 230 volt actuators are always the better choice, as most KNX heating actuators in 230 volt mode can switch several actuators simultaneously on one output.
This has to do with the current load, which is higher at 24 volts and therefore the switchable power is significantly lower than at 230 volts. So: Stay away from 24-volt actuators!
Comparison of the 3 operating modes of a KNX heating actuator
The following 3 operating modes can be used by all five test candidates and are, so to speak, standard features of every KNX heating actuator. In our experience, this topic in particular is not properly handled and understood in many KNX installations. If you are confident enough to program and set up KNX in a house yourself, you can download our click guide to KNX programming in 8 hours in 8 hours.
2-point control: For electric heating, air conditioners
The simplest operating mode of a KNX heating actuator is 2-point control. The heating is switched on and off without any intermediate values. The switching command (on/off with 1-bit group address) comes from an external room temperature controller, which can be a KNX push-button. See also our top 30 longlist comparison of the best KNX push-buttons.
This operating mode of a 2-point controller is used for purely electric heating systems and electrically controlled ventilation flaps. This also includes the increasingly common air conditioning units in rooms.
Continuous PWM control: For underfloor heating & ceiling heating
The most commonly used operating mode of a KNX heating actuator is continuous PWM control. PWM is an abbreviation for “pulse width modulation”. Here, a 0 to 100 percent control value (with a 1-byte group address) is specified and sent by a room temperature controller.
Continuous PWM control is always used for underfloor heating and wall/ceiling heating in new buildings and for component activation/concrete core activation. The background: Due to the large quantities of water in the concrete/screed, such water heating systems are very inert. The main advantage of continuous PWM control lies in the premature reduction of the heating output when the actual value quickly approaches the setpoint. In this case, the heating circuit control valves are already closed gradually, even though the setpoint value has not yet been fully reached.
With this control system, room temperatures can be maintained and ensured very precisely. And how does it all work? The desired setpoint is set on the heating controller – for example a KNX push-button. The heating controller in the KNX push-button measures the current room temperature and uses this to calculate the control value to be sent. Unfortunately, some KNX push-buttons do not have an integrated heating controller -> see our Top 30 comparison of the best KNX push-buttons.
The advantage over all other controls of a heating actuator: With continuous PWM control, rapid temperature changes are counteracted prematurely.
The KNX heating actuator converts the continuous manipulated variable signal (group address with 1 byte 0 to 100 percent) from the heating controller into corresponding switching pulses within the set cycle time. This process is called pulse width modulation, whereby on/off signals are modulated within a PWM cycle.
Here is a setting that we made on all test candidates as an example:
PWM cycle set = 8 minutes
Control value = 75%
Result: the heating actuator opens the control valve for 6 minutes and closes it for 2 minutes. With a set PWM cycle of 30 minutes, the control valve opens for 22.5 minutes and closes for 7.5 minutes.
Integrated controller: For rooms without a room temperature controller
Now we come to the third operating mode: the integrated controller. This means that the heating controller is used in the KNX heating actuator and a temperature sensor is evaluated in each room to be controlled. This can be a KNX push-button or a KNX presence detector, although the latter is not necessarily the first choice when it comes to precise measurements at “body height”.
Typical applications for using the “integrated controller” operating mode in larger buildings are rooms that do not have a KNX push-button with integrated room temperature controller and therefore require external control. The same applies to company or commercial buildings that have large rooms without push-buttons.
1st place: MDT AKH-0800.03 KNX heating actuator 8-fold
The heating actuator from MDT has been available in its highest expansion stage with 8 outputs for controlling actuators since 2020. Like the other manufacturers in the test field, MDT is a German company with a relatively short KNX history compared to the competition, but an even more extensive product range.
MDT is going full throttle, especially with KNX actuators and their features, including the heating actuators. With a narrow width of 72 mm (only 4 TEs), the manufacturer packs 8 outputs including status LEDs into its KNX heating actuator. A maximum of 4 actuators can be connected to each output: This makes a total of 32 actuators, which can be sufficient for many a detached house or even a new-build apartment. If you need more, simply use several heating actuators.
In contrast to the other test candidates, MDT has dispensed with the option of manual operation on the heating actuator itself, so that the 8 outputs can only be switched via the KNX bus using software. MDT has visibly saved on the simple housing and workmanship, but this does not affect the functions.
The MDT heating actuator supports the three familiar operating modes – continuous PI control, switching PI control (PWM) and switching 2-point control – just like the other competitors. One special feature: the settings in the ETS software are clear and much easier to understand than those of ABB and Hager, for example.
It goes without saying that the MDT AKH-0800.03 supports both heating and cooling operation. The latter is essential today in conjunction with a frequently used air-to-water heat pump, even in the lower house construction price segment, so that it is possible to switch to cooling mode in summer when temperatures are hot. Finally, the heating actuator must also support this in order to enable room temperature control via KNX button or touch panel. Or everything can be completely automatic without any external intervention, whereby a good deal of practical experience is required for parameterization/programming.
We probably don’t need to mention the typical modes such as “Comfort”, “Night reduction”, “Standby” and “Frost/heat protection” here, as these have been available for KNX heating actuators for over 15 years and are hardly relevant in practice.
All in all, the MDT AKH-800.03 heating actuator takes first place with its good features, its outputs for 32 actuators, the simple housing (with processing flaws) and its very reasonable price of approx. 140 euros. Or to put it another way: the output for 32 actuators costs 4.38 euros/output. This topic is often discussed in DIY forums and less in our environment. No other competitor offers such a low price.
MDT AKH-0800.03 KNX heating actuator 8-fold Rating
Overall ranking: 1st place
2nd place: Theben HM 12T KNX heating actuator 12-fold
The German company Theben has been offering high-quality KNX heating actuators for almost 20 years. The top model is the Theben HM 12 T KNX with a total of 12 outputs for controlling actuators. With a width of 144 mm (8 TEs), the heating actuator takes up twice as much space in the control cabinet as the MDT AKH-0800.03 (with 8 outputs).
Theben allows the connection of up to 36 actuators via the 12 outputs and is therefore also suitable for a larger detached house with 3 to 4 floors and approx. 180 to 230 square meters of living space. As usual with Theben, the settings in the software are logical and almost self-explanatory. In the past, we have very often carried out our technical planning with heating actuators from Theben, as the support and updates have also suited us.
For those who prefer convenience, the Theben heating actuator is also available in a version for placement in the heating circuit distributor. This saves on the power cables and the KNX cable is routed to the heating circuit distributor instead. We don’t do it this way, nor do we recommend it, but there are still some “electricians” who like to install it this way.
Theben HM 12T KNX heating actuator 12-fold rating
Overall ranking: 2nd place
3rd place: Elsner KNX K8 heating actuator 8-fold
Elsner Elektronik from the Black Forest offers the K8 heating actuator, its largest actuator for heating control. With a width of 107 mm (6 TEs), it takes up little space in the control cabinet.
Elsner provides each channel with 8 watts of power, so that theoretically a maximum of 8 actuators (each with 1 watt) can be connected to one output. Wow, no other test participant can do that! This means that a total of 64 actuators can be controlled at the 8 outputs. As with all other test candidates, all outputs on the Elsner heating actuator can be set as heating controllers or as “classic” heating actuators. Manual operation is available with LED status displays, which can be switched off in the software if required. Overall, the Elsner K8 heating actuator is not quite as well equipped as MDT and Theben, but it still commands the highest price in this comparison test. In terms of price per channel, it comes in second place behind the MDT.
Elsner KNX K8 heating actuator 8-fold rating
Overall ranking: 3rd place
4th place: Hager TXM646R 6-gang heating actuator
The German company Hager is family-owned and a veteran in the KNX world. It has been offering many products for networked building technology since the early 1990s. The Hager TXM646R heating actuator occupies a special position in this comparison test. It can control up to 24 actuators of any heating system via the 6 outputs.
It also has 12 (!) integrated heating controllers, which can also be used externally beyond the 6 outputs. The power cables can be connected very conveniently via the terminal outlets on both sides – top and bottom. No other test candidate offers this in this form. In addition, the price is very reasonable and almost on a par with the MDT (in first place).
The settings in the ETS product database appear somewhat outdated; the company’s focus on functional and commercial building construction is clearly evident here. However, Hager could just as easily be found in the detached house and residential sector.
Hager TXM646R Heating actuator 6-fold Rating
Overall ranking: 4th place
5th place: ABB VAA S12.230 valve drive actuator 12-fold
At ABB, the KNX heating actuator goes by the name of valve drive actuator, which we have included in this comparison test in the version with 12 outputs. As with most of the other candidates, the heating actuator can control corresponding actuators with 24 volts and 230 volts. The software configuration and parameterization is somewhat reminiscent of the early 2000s; ABB should urgently improve the user interface and adapt it to 2024.
The Swiss company ABB, with its headquarters in Zurich, is one of the founding fathers of the KNX standard, as are a number of other companies. The first KNX actuators appeared on the market at the end of the 1990s and were primarily used in private villas. ABB specialized early on in the development of good KNX actuators and left the design of KNX push-buttons to other companies.
A total of up to 36 actuators can be controlled via the 12 outputs of the ABB VAA S12.230. heating actuator. In terms of price per actuator output, this puts ABB in the middle of the field.
ABB VAA S12.230 Valve drive actuator 12-fold Rating
Overall ranking: 5th place
Conclusion
When it comes to the best price/performance ratio of all KNX heating actuators, the MDT AKH-0800.03 heating actuator with its 8 outputs is by far the best. Added to this is the fact that up to 32 actuators can be connected to the MDT heating actuator for heating control – with a width of just 72 mm in the electrical control cabinet. This is enough for many “normal” detached houses up to 160 square meters or larger apartments. We have listed it in the table above:
MDT comes to 4.38 euros per actuator output if all 32 possible actuators are used. The manufacturer has dispensed with “manual operation”, which is acceptable in view of the many good features. On closer inspection, there are compromises to be made in terms of workmanship and quality of detail, but these should hardly bother anyone as the MDT heating actuator disappears out of sight in the electrical cabinet. Overall, the MDT heating actuator comes in at number 1.
1st place
2nd place
3rd place
4th place
5th place
Among the 12-way heating actuators, the Theben HM 12T KNX is the best choice for controlling up to 36 heating circuit valves. We have been particularly impressed by the good and very simple software parameterization for years, which can also be found in the top model HM 12T KNX. The manual operation via buttons on the actuator and the LED status indicators convey a very good impression of quality that no other test participant can offer. In terms of price/performance ratio, Theben is more in the middle of the field.
The third-placed Elsner KNX K8 heating actuator is unrivaled in terms of switching capacity: according to the data sheet, 8 watts can be switched per output. With an actuator with an output of 1 watt (as we often use), this theoretically results in up to 8 heating circuit valves per output and 64 heating circuit valves in total on the heating actuator. We have not yet tested where the practical limit really lies.
The Hager TXM646R 6-way heating actuator plays a special role, because despite its 6 outputs, it has 12 integrated heating controllers (the “R” stands for integrated heating controller). The configuration in the ETS software allows a wide range of options and in terms of price, Hager is in second place – which was not to be expected – just behind MDT.
Despite its 12 outputs and the control of up to 36 heating circuit valves, the ABB VAA S.12 Heating actuator not so convincing. The configuration in the ETS software is really reminiscent of the early 2000s! The outdated terms and designations can also only be understood straight away by “KNX insiders” who are very deeply familiar with the subject. In terms of price, ABB ranks more in the mid-range, although this should not be a purchase criterion for this heating actuator. The ABB heating actuator ends up in the project business anyway, where completely different rules apply in the context of tenders.
Frank Völkel & Smartest Home Team
Since 2007, we have been testing KNX components for functionality and practical suitability in order to use only the best products in our customers' homes and villas
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