The Z-Wave Thermostat – Test: Devolo / Danfoss vs. Eurotronic Comet-Z

by AlphaX216. January 2016

After my first tries with a few intermediate switches and the kind of fractious Fibaro Smoke Detector, I already reported about the possibility to create a heating schedule. Today’s topic will be the matching thermostat…

First of all, all of you will be wondering, which thermostat is supposed to be the one. To be honest, there is not that big of a choice in the Z-Wave area, because at the end it is going to be one of three products anyway: Danfoss (or an alternative of it), or one by Eurotronic: the StellaZ, or the new Comet Z-Wave. The StellaZ, as well as the Comet are at around 50 euros cheaper than the alternatives by Danfoss, which are available for 60 euros resp. 70 euros if you want to get the Devolo version. A clear disadvantage regarding the StellaZ: manual regulation is not possible – a no go to me. Besides that, its processing and sound intensity are not expected to be that good either. For this comparison it is going to be the Danfoss LC13 (LC13 is the most current version), the Devolo-Equivalent and the new Eurotronic Comet. Whoever is using the StellaZ should feel free to tell us about his or her experiences in the comments!

Packaging and Content


The Danfoss comes in a small plain carton, along with: a small instruction, a few (Sony)-batteries (R6/AA), two adapter-rings for the usual heating connection, a small Allen key (later on needed for the demolition) as well as the thermostat itself and a short instruction, this unfortunately comes without any parameter information. Devolo on the other side, uses a big package for the small white Danfoss box and puts an own supplementary sheet instead of an instruction next to it. Looks precious, is actually not more than the Danfoss original though.



My test-sample of the Eurotronic COMET came in a white carton as well, though, it came along with adapter-rings for various heaters only. Other than that, nothing. Unfortunately, batteries were not included. The Comet will also need AA/R6 batteries, this means the following costs will not be that high, particularly as a lifetime of around 1,5-2 years seems realistic. Needless to say, a start-instruction in form of an A4 paper is included. It is Comet-zwave-BDA_eng. It actually explains everything important (e.g. the inclusion), furthermore the supported Z-Wave Command-Classes are listed on there, as well as described – for the experts.


Eurotronic Comet – Display & Adjusting Wheel

Processing and first installation


I would describe the quality of the thermostat as pretty good, only the cover of the battery compartment seems a little cheap and as if it was an easy game. Other than that everything is made of plastic – this also concerns the adapter-rings. One would have to answer for oneself, if this is a real disadvantage. The buttons are fastened neatly and should be able to handle many manual operations as well, though they have a pretty big gap to the case and the pressure point is kind of spongy. Talking about gaps, who tries to take a look into the case, will be able to discover the circuit board, which therefore has to be positioned pretty free, this could be a possible problem in moist rooms, such as bathrooms!

The Installation at the heater is actually rather easy: take the old regulator down, screw the matching adapter-ring to the heater and onto it the thermostat. I needed two tries to do it, though, because at the first one the thermostat did not really sit quite right on the adapter. You will notice, if it is right, if at some point you reach some kind of an “idle”. It then can be twisted (kind of shaky) without an end. After turning on the thermostat, it fastens and then sits on the adapter-ring properly. You are offered three buttons for the operating, those are used for on/off as well as the temperature regulation (+/-). They are placed on the right, left, and under a small, lit up display, which shows the temperature and some status information

Chris already took a video . of the installation process in his report about the Devolo Smart-Home solution. Unfortunately, Devolo assumes that their products are only used with the Devolo-Central Station. The Devolo-Central Station would then also explain how installation, inclusion and other settings are taking place. There actually is nothing helpful written in the supplement paper, regarding the usage at unknown central stations, such as the RaZberry. For those interested, there are Danfoss handbooks on the internet, which at least explain the installation process and similar. After mounting the thermostat can be twisted, as protection against damage, in case the visit should want “to rule classy”.

These start information directly come along with the Danfoss-alternative. Therefore, the inclusion worked easy with Devolo as well as Danfoss, even though it took a second try in the bathroom. I am assuming that this was because of the missing Z-Wave Plus. So you might want to include first, and then mount. The Mesh-Networking interferes in the later usage, which means this point is becoming untenable. The inclusion in the living room, which is much closer to the Raspberry, took place without any problems. I then also downloaded the Danfoss LC13 device description for both devices in the Z-Way Experts-Surface, even though it does not match the Devolo 100 %, since Devolo uses a modified firmware. The integration and recognition in the ZWay-Software on the other side works without any problems, the elements for thermostat and temperature were neatly placed directly and so far function like they should, in addition to that they are absolutely self-explaining.


When first taking the thermostat out of its packaging and taking a closer look at it, its massiveness directly caught my attention. It seems kind of chunky and the design is a matter of taste. To me it is, once it is mounted to the heater, pretty good. In my case, the WAF is in an area of >1%, though. This might also be due to the fact that the batteries are placed upright in the front and not horizontally, as in the case of the Danfoss-alternatives. Due to that, the front is pretty massive already. Other than that, it is conspicuously that other than a simple, pretty big digital Display there is only one rotary wheel. In the other versions of the Comet, e.g. with Bluetooth or DECT this is accompanied by buttons. Pretty good: The rotary wheel, as well as the display are directed upwards and can therefore be reached easily.

The temperature on the Z-Wave model can be turned up resp. down via rotary wheel, other setting possibilities are not provided, though. A disadvantage: The display comes without lighting – this means there will not be any manually adjusting, or reading without additional light. The installation to the heater is almost even easier than at the competition-model by Danfoss, if no adapter-ring is needed, you simply screw the Comet to the heater, like a classic hand regulator. And in contrast to the thermostat, the screw-nut is also made of metal, instead of plastic, this is why it holds on tight, is stable and as a matter of fact you cannot do anything wrong with it. I would describe the remaining processing as pretty good as well, nothing ratters, nothing wobbles. Once the thermostat is screwed on, it still can be turned. This makes a flexible positioning of the display/rotary wheel possible. Additionally, nothing can be damaged by turning it by mistake.

Regarding the topic inclusion, I simply want to refer to Chris’ comment. By the way, I actually am a reader of handbooks, but the handbook was not included in the prepackaging and I did not have the PDF in hand either. Oh, and since Chris was already messing around with my Comet before, he was not even excluded – how much nerves that would cost should be obvious, right? :-D But even with the handbook, I still think that the process and especially this “button” are a pretty bad solution. Also strange: with Z-Way, the exclusion and inclusion only worked on the standard surface, not on the expert-surface, though. Other than that, the thermostat was (pretty much) taken over neatly. A little stupid: two elements do not function correctly. One element is shown with whom the Valve-opening is supposedly able to be set into percent. This does not really work, though. The sense could be argued about as well: how much Celsius is e.g. 30%? This would have to be experimented on forever, until the matching values were found. The second element is some kind of fast-setting, which offers following modes: Off (remains at 8°C), Eco-Mode (18°C e.g. overnight), heating/comfort-temperature (22°C) and a “Manufacturer specific” mode – turning back and forth between Eco/Comfort. So far, I at least understood Eurotronic. These modes can only be used in the Expert-UI, though, in the normal surface there will be a simple on/off switch. A dropdown-menu would be much better in this case, the element is as you could almost say, not useful. That is why I faded out both of them. Whoever is working with the API, should be able to use it though, in this case it could even be useful.

In the daily Usage


Like all other Z-Wave devices with battery, the thermostats are asleep most of the time as well. The standard-time it takes them to wake up is set at 5 minutes – this allows new settings to be adopted pretty quickly. Of course, another time can be chosen as well, but I certainly want it to get warm as fast as possible, after I adjust the heater. And most of all: the thermostat is nearly inaudible while it is working. You actually have to stand right next to it to be able to hear that there seriously is something going on. I really listened to some louder ones before.

Only thing I can say about the Danfoss and Devolo is: So far, it adjusted everything pretty well and adopted all temperatures nicely, during the last weeks, thanks to the short interval, I could barely detect any delays. One thing that I was worried about in the beginning is: when dismantling the old hand regulator, I turned the heater up completely, so that it was way too hot for a few minutes. Though, the heaters are warm pretty fast, which affected the intern temperature-regulator of the thermostat. This is why the temperature sensor still showed a temperature of about 25 °C after 1,5 h, when I had already set up a temperature goal of 14°C for during the night, though. It rather felt like 18-19°C, since the room was aired before the little alteration. By now, the intern measuring turned out to be pretty reliable, though, and is delivering identical values as a classic room thermometer.

Even though, the sensor is placed in the thermostat itself. Here comes the problem: only users that decide to use the Devolo-version get the chance to try this intern measuring. This is due to the fact that the firmware was adjusted to report the measured temperature of the thermostat to the basis, in the case of Devolo. The Danfoss version on the other side uses these intern measurements to reach the admired temperature – the basis does not get these information, though. This is why it is definitely worth it to choose the slightly more expensive Devolo-model, because another measurement in a room with wall thermostat, or similar is not needed anymore. Especially, because a Devolo/Danfoss wall thermostat is pretty pricy. This would only be worthwhile, if several heaters should be controlled at the same time.

Real disadvantages are my heaters: the connection for the regulators is placed on the side of the heater, instead of in the front. Even though this means that classic regulators can be turned comfortably, it is pretty hard and also effortful to read the display. Due to that, the manual changing of the temperature can turn out to be pretty acrobatic as well.


What shall I say. At my home, everything is time-controlled currently and there were no problems yet. Temperatures are adjusted nicely, the adopting works and the temperatures match the adjustments. I set the interval of the Danfos/Devolo devices to 5 minutes, the actual 15 minutes seemed pretty long to me. Especially, because you have to think of the heater, which needs some time until the room is on temperature as well. By the way, the Eurotronic Comet also delivers the temperature it measures in the moment. This means, it serves as a room-thermostat resp. you do not necessarily need an additional one, just like the Devolo version does too. The volume is limited as well, while it is completely silent, a slight hum can be heard, this is recognizable, does not really disturb, though. So far, so good.

Though, the manual adjustment gets a little strange, this affects two points:

  1. First of all, manual adjusted temperatures are not sent to the basis. This is somehow incomprehensible and actually only known from very old adaptors, I simply do not expect something like that from current Z-Wave devices.
  2. Point two is a double-edged sword: if the temperature is manually set up at the rotary wheel, the thermostat is in the „Manual Mode“ and cannot set a new temperature for 2h. In order to do any adjustments, the thermostat has to switch back into the „Auto-Mode“ first. This feature is not optional though, but rather always active!

I can think of advantages and disadvantages in an equal number. A positive one: at 8pm the temperature will always be at 14°C, in the bathroom as well. If I want to take a bath now, I simply turn up the temperature manually and the basis has no access – even two hours in the bath and I do not have to freeze. With that we are at the negative side: I must not forget to manually set the temperature to 14°C neither. To regularly let the basis check, which temperature is set up via script? Not that bad of an idea, does only work if you directly call up the temperature though, since it is not reported. This ensures a lot of radio communications – not that ideal.

What should be said as well

By the way, all thermostats have an open-window-sensor. In case the temperature should drop rapidly, they turn off. The combination of a door/window contact would be better, of course, since the heater would then already turn off before the temperatures drop noticeably. But attention: they all only turn off for a limited time: Danfoss/Devolo for 30 min., the Comet for 15 minutes. It should not matter to the ones that air fitfully. Though, in this case a door/window contact would be an advantage as well. The heater usually does not directly turn off when opening the window, and also not directly on when closing it. The Eurotronic is missing out on child protection as well, if you should have small children, you should always watch out that nothing is changed, especially because you do not get any information to the basis and also have to switch back during the next two hours. Things like frost or cold protection are available for all of them, this means something will automatically be heated up before your heater freezes and the valve goes back and forth in regular intervals to prevent a fixing of the valve/thermostat to its place.


I think it is obvious: objective clear favorite is the Danfoss thermostat, the Devolo version, though. The device and the features are identical, only the Devolo-Firmware reports the temperature and this way provides the best overall package with ~70 euros, though this is the most expensive version as well. In case you should already own door/window-contacts, and want to integrate these, or another sensor with the temperature sensor in the room, or even want to use a wall regulator, you can choose the around 10 euros cheaper Danfoss Original. The ones that strictly have to watch the price, or can go without some features (feedback of manual temperatures, child protection) can choose the Eurotronic Comet. You really do not do anything wrong with that, especially since it is the cheapest one of them with about 50 euros, which you should not forget. Next to that: I think the display, which is directed upwards and the adjusting wheel are real advantages in comparison with the Danfoss-versions. The Eurotronic model is already available at relevant retailers. The real cracker would be, if Eurotronic would come up with a “Comet 2” with new firmware, – maybe in a few months – which would implement child protection and solve the manual problems.

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