Best retrofit smart home new build

what writes is exactly the crux of the matter. Air wants to move to the coldest point. So the warmed air in the warmer rooms will heat the cooler rooms. Of course, this also means that the heating system has to "work against" this in the rooms you want warmer and is therefore less efficient. If a controlled residential ventilation system is also involved, which is likely with KFW55, regardless of the standard but recommended anyway, this effect is further intensified. The solution for you would probably be to adjust the hydraulic balancing so that the generally desired low temperatures are achieved, and in the rooms where it can be warmer, to work with additional heat sources, such as infrared heaters, locally as needed. For example, when showering or whatever. Anything else will lead to a temperature equalization throughout the house. Edit: You should also not orient yourself to the 22-23 degrees I mentioned. Those are the temperatures we told the heating engineer. Accordingly, the heating system was designed. You say, you want 20 degrees (or whatever) and have the heating system designed accordingly. Whether it is 20, 22, or 30 degrees, the principle remains the same. If I adjust the heating by only 0.5 degrees, we notice it only 24 hours later. This will never work for individual rooms in a modern house.

How about lights and blinds? I was thinking about actuators like Shelly or Sonoff behind the switches (the whole house will have deep boxes)

You can do that. You are then 100% dependent on a working Wi-Fi in every corner of your house.

That reminds me – ventilation system – does it make sense to make it smart somehow?

Always this "smart"... just because something is operable via an app doesn't mean it's smart or smartly done. The ventilation usually regulates itself. One could consider programming a party mode into the visualization, but even increased occupancy will eventually be noticed by the system itself.

You can do it that way. But then you are 100% dependent on a working Wi-Fi in every corner of your house. Always this "smart"... just because something is operable via an app doesn't mean it's smart or made smart. The ventilation usually regulates itself. You could consider programming a party mode into the visualization, but with increased occupancy, the system will notice it by itself eventually.

On both floors, there is an access point hanging right in the middle of the house. Actually, I would like to control the whole thing via Zigbee. Because I have a friend who has many Shellys and already had some problems (Web UI very slow) with his FritzBox 7390 (probably due to the many Wi-Fi devices). But actually, such a FritzBox should be able to handle that. That's why I'm still torn. Could someone recommend good Zigbee actuators for light switches and roller shutter switches? I am aware that smart doesn't simply mean "app," I just wanted to ask to maybe gather suggestions or ideas.

So normally, FHBs are also equipped with valves during construction. I don't know of a single construction site where there are no room thermostats or valves. Slow response or not. Regardless of whether it's residential construction or single-family homes.

When building with KFW, individual room control is even mandatory as far as I know.

Unobtrusively reporting. We have neither EER nor control valves [plumber performed hydraulic balancing]. We built with a general contractor (KFW55) and were told that we would retrofit this ourselves (had Homematic IP wireless room thermostats in mind). Currently, we do not use any ERR. Neither the commissioned electrician nor the general contractor was really interested.

edit: Homematic IP can also be well integrated into HomeAssistant
edit2: Also for the ventilation system – in my case Vaillant RecoVair – there is a corresponding interface. I have everything in HomeAssistant and can set up my automation there

Ventilation usually regulates itself. One could also consider programming a party mode into the visualization, but even increased occupancy will eventually be noticed by the system itself.

Is that so? Regarding ERR, I understood the principle and it definitely makes sense. Regarding controlled residential ventilation, I am currently not sure if that is the case. Do they really regulate themselves? But don't controlled residential ventilation systems just have 3-4 levels and are basically operating with constant airflow rates? One could basically do it the same way as with underfloor heating: measuring relative humidity, temperature, and CO2 at the outlet, for example, and then controlling the total airflow, but is that actually done? And would that even work, or is the sensor technology too inaccurate here to detect fluctuations in the values when measured as a whole and not per room?

So, I am not very knowledgeable on the topic; these are just thoughts I have had and are not based on real expertise. I would therefore appreciate clarification on how it actually works in practice.

The only thing that the recoVair from Viallant controls is the ventilation strength time-based on 2 patterns day/night. You can also add an offset when a certain humidity or CO2 value is exceeded, but this refers to the set ventilation level - at least with the RecoVair -