Which smart home system to retrofit?

Google helps a lot if you enter "BEG" or "Bundesförderung für effiziente Gebäude". A lot changed there in January. Generally, it is about the promotion of everything related to energy saving and the connection of the involved trades. It has nothing to do with the KfW loan. However, if your developer obviously has no idea about the topic itself, I find it very interesting when he is supposed to write you eligible offers. For that, you would have to 1. know what is even possible in the field of building automation and 2. what of that and in which combination is eligible for funding. I see this very pessimistically for you.

There are already other , where you can get a feeling for what is all funded.

-....other forums that deal more thoroughly with the respective smart home systems.

Which forums are those? With the multitude of terms, protocols, and providers, I feel lost in the jungle...

Which forums are those? With the multitude of terms, protocols, and providers, I am completely lost in the jungle...

They are usually directly manufacturer-specific. Unfortunately, other forums are not allowed to be referenced here or it usually happens very cryptically. What are your requirements?

I am still collecting them... :-) But I would like to see through and understand the whole jungle.

It depends on what you want. Everything available for retrofitting always has an island character. In other words, they can usually cover 1-2 things well but never everything, so it often ends up being a wild mix of several things that "somehow" work.