ᐅ New Construction with a Granny Flat – Heating System and KfW Financing Questions

Hello housebuilding friends,

Since I have a large thread with many questions, I will separate the individual questions. It was quite a surprise that we got a building plot.

A house construction is planned. New build according to KFW40+ standard (currently still undecided whether KFW55, 40, or 40+). Using the new KFW subsidy would cover the additional costs one-to-one.

Yesterday during planning, I learned that for the new build, I will get "2x air-to-air heat pump heating" installed. Since I can apply for the KFW subsidy twice, I need 2 heating systems. What sense does that make? Well, in the end, I will probably get the heating for the secondary apartment (SA) at no extra cost.

The house (timber frame prefab house) without a basement, spread across two levels. 160 sqm (1720 sq ft) main apartment, 65 sqm (700 sq ft) secondary apartment.

Ground floor – main apartment + secondary apartment and the utility room
Upper floor – remaining rooms like children's rooms

The builder has now planned a "small and a large air-to-air heat pump" in the utility room.

My plan is rather to switch to an air-to-water heat pump with underfloor heating (should I also install a ventilation system with exhaust air heat recovery at the same time?). But what is sensible for the secondary apartment? Use the air-to-air heat pump of the main apartment and also install underfloor heating there? Here in the forum, I often read about the Panasonic Geisha monoblock. Would that be an option? So many questions...
I am honestly overwhelmed and still at the beginning of sorting out all these topics for the new build. Since a photovoltaic system is mandatory for new builds, it should be sized accordingly.
Then I would rather go for KFW40 without battery and cover the entire roof with panels.

I’m not sure if this information is sufficient to make a meaningful statement.

Thanks everyone.

Best regards,
Ben

Addendum:

The house (timber frame prefabricated house) is distributed over 2 levels without a basement. 160 m² (1,722 sq ft) for the main residence and 65 m² (700 sq ft) for the secondary unit.
The current offer is for a Bien-Zenker turnkey house. However, I could also get the house as a shell (shell construction) and subcontract the heating, photovoltaic system, and interior finishing work.

derBensch schrieb:

I often read about the Panasonic Geisha Monoblock here in the forum. Would that be a good option?

As far as I know, that is mainly a heat pump for DIY enthusiasts. It is very affordable and performs well. However, assume that companies like Bien-Zenker do not install “something like that.”

An air-to-air heat pump is generally intended for passive houses. It is very inexpensive because it does not require underfloor heating. Using two air-to-water heat pumps along with underfloor heating will result in significantly higher costs. Especially since a controlled mechanical ventilation system would also need to be added (which is basically standard for a “comfort heating” system).

Then I need to request an offer for the underfloor heating with an air-to-water heat pump so that I can get an estimate of the cost.
The Geisha can be "laid aside" for now.

What would be your recommendation then? Especially regarding the two heating systems?

I think having two heating systems is great. No billing issues. Everyone can operate their heating according to their own preferences. And the additional cost from one to two should be reasonable.

P.S. I am currently renovating a two-family house. It will be KFW 55 standard – each apartment will have a Panasonic monoblock ;-)
So just do it the way you want.

So, 2x air-to-water heat pumps (are there any advantages to choosing a split system?) would also be offered by Bien-Zenker (I am currently waiting for the quotes). I assume the photovoltaic system offered by Bien-Zenker then powers both heating units? It probably won’t be sufficient.

Are there any other opinions or experiences? How have others here solved this?

Regards, Ben