As for planning/design of energy standard and heating concept

Hello, first of all thank you for all the input. I will address various points later.

But first a question about the recommended topic, which among other things also lists the example calculation of the different heating systems:

Accordingly, the air-to-water heat pump would be significantly more attractive than the gas heating. But apparently the calculation does not seem quite realistic regarding the electricity costs. Can someone say something more precise here? Where is the mistake or the "neutral" in this calculation at all?

At least I had the feeling that I would be much better off with the AWHP than with gas. However, the majority of opinions here in the forum often tend towards gas.

Regards :)

Gas is especially easier to use for rental properties. You always get the complaints "Cold, we're freezing, turn up the heating...." And gas is easy to maintain by any installer, even by those resistant to further training!

Do you still get the KFW funding twice nowadays for 2 residential units (granny flat plus own)?

If yes, you should check that again......We did it but not because of the "great" conditions but to be more flexible.....with us you could still make special repayments without limit and the loan ends already after 10 years and then our monthly burden finally drops significantly..

Think again carefully about the 36.5 if you have tenants, you should actually take something filled! The tenant will have no desire to hear the noises you make downstairs.......and if you take something filled you are almost back at KFW 55. You have to apply for the funding beforehand.....and watch out for the impact sound insulation.....

Take gas. See other thread and comment from BoxandProof.

Decentralized I would only do it myself in the bathroom because of comfort, otherwise the things are too loud for me to keep them running constantly in the living areas. But maybe there are better devices by now.

Yes, there are still subsidies for multiple residential units.

General question again regarding ventilation: From when is it actually "mandatory" and how is this even monitored? Or is it more in the direction of an "unwritten rule", you should do it because due to the tightness of the house it eventually just makes sense?

I am missing the hard criterion there.

It is not mandatory. but you should not build without some kind of forced ventilation, regardless of whether it is for rental or personal use. The houses are too airtight. That is not healthy and quickly leads to mold in corners. - The cheapest type are window rebate vents.

But first, a question about the recommended topic, which among other things lists the exemplary calculation of the different heating systems

You have to calculate that yourself for your residential units and with offers. The example is just an example and without a source. For us, everything looked completely different. Also, every supposed expert will tell you something different, so inform yourself, calculate yourself, or just take gas and not think about it anymore. You also need the right craftsmen for everything; that was the biggest hurdle for us to get the affordable heat pump installed. But it was worth it.

I would do:
Apartment: Separate gas heating, hot water without storage. Decentralized/simple ventilation with or without heat recovery.

And for your residential unit either
a) simple: gas, then possibly together with the apartment.
or:
b) well-planned heat pump with 1. trench collector laid by yourself + subsidy or 2. a simple inexpensive Japanese air-water heat pump without indoor unit (no split).

Ventilation for your own unit at your own discretion, purely comfort. Central with heat recovery is then the optimum. Avoid solar thermal if possible, photovoltaics definitely.

Funding opportunities for both units was a good tip, KFW has become somewhat more attractive again.

And how does it work with the KFW funding? Presumably, many things will only be decided during the construction and then at short notice. Can I still get such things funded at short notice, or do I have to have applied for everything well in advance?