KfW 40+ funding with photovoltaic and ventilation system

Hello everyone,

Currently, we are facing the decision of which efficiency class we should install.
It is going to be a prefabricated house with 150 sqm with a fireplace for 2 adults and 2 children, with an air/water heat pump by Stiebel Eltron (probably LWZ 5 S).
The heating system is offered to us by the prefabricated house manufacturer.

For the KfW funding, we received the following offer:
(I leave out insulation)
LW_WP+ventilation
16.37 sqm FH_PV system (9 modules each 390Wp 3.51 kWp south-oriented 25* attic
1WE usable capacity 2.6 kWh
Manufacturer: BYD Premium HVS 5.1

Unfortunately, I have read many negative things about a ventilation system and am quite reluctant.
In addition, a lot is said here about a photovoltaic system (installing many modules and a small storage).

For the entire package (photovoltaic + ventilation) I would have to pay €21,000.

Can you please help me?

Does this variant make sense? Can something better be installed afterward?
I want to act very cautiously, as I am not very familiar with this.

I would be grateful for any answer.

Unfortunately, I have read a lot of negative things about a ventilation system and am relatively averse to it.

I actually read almost only positive reports about a controlled residential ventilation system (and I also confirm these reports myself). What have you read?

16.37 sqm FH_PV system (9 modules each 390Wp 3.51 kWp south-oriented 25* attic 1WE usable capacity 2.6kWh

That is just a token system. Fill the roof.

That's just a token system. Fill up the roof.

I can only support that! 3.5 kWp is really ridiculous!

16.37 sqm FH_PV system (9 modules each 390Wp 3.51 kWp south-oriented 25* attic
1 residential unit usable capacity 2.6kWh
Manufacturer: BYD Premium HVS 5.1

I can still understand the idea of taking a small battery to take advantage of the subsidy. But as mentioned, the size of the system is a joke!
Fill the roof properly. That means ideally already thinking about photovoltaics during the roof planning (plan extensions/bay windows so that photovoltaics can be smoothly installed there).

Normally, you should get around 8-15 kWp on a single-family house.
Then select the battery accordingly... about 30-60% of the kWp capacity of the photovoltaic system.

As already described here: Fill the roof completely. Better look for separate offers. The ones from the house manufacturer are always much too expensive, they only cover the token systems.

What bad things have you heard about ventilation systems? At most dry air. Otherwise, you mostly hear negative things about air-to-air heat pumps (that is, heating through the ventilation system).

As already described here: Fill the roof completely. Better look for separate offers. The ones from the house manufacturer are always way too expensive, as they only cover token systems.

What bad things have you heard about ventilation systems? At most dry air. Otherwise, you mostly hear bad things about air-to-air heat pumps (i.e., heating via the ventilation system).

As you already wrote, the dry air. That causes me the most concern, otherwise contaminated ducts, through which bacteria can form.

As you already wrote, the dry air.

First, the air is always dry in winter (even without controlled residential ventilation) and second, you can also choose a variant with humidity recovery.

That worries me the most, otherwise contaminated shafts, through which bacteria can form.

Bacilli form in moisture. But you yourself write that the air is too dry for you. You have to decide. Both can’t work ;-)
Apart from that, the systems do not “get filthy” if you treat them properly (regularly change filters).