ᐅ KfW 70 with gas-solar heating system

Hello, we plan to start building our own home this year.

I already have two active discussion threads on this forum about it.

https://www.hausbau-forum.de/threads/Hausbau-kfw70-ca-150m-welche-Heizung-Gas-lwwp.12261/
https://www.hausbau-forum.de/threads/wir-wollen-bauen-ist-das-was-uns-angeboten-wird-so-i-o.12269/

We just got back from discussing the offer with the supplier.
I tried to talk about heating and ventilation; he shared his experiences, opinions, and advice.
This didn’t quite match what I had read so far, so now I’m uncertain and confused again.

We requested a 150m² (1,615 sq ft) solid house built to KFW 70 standard.

This is achieved through insulation and a gas-solar heating system. More details are in my other threads.

When I asked about a mechanical ventilation system with heat recovery, he said it’s not needed, that regular airing is sufficient.

He also said his son built a KFW 70 house with gas-solar three years ago and that he would never do that again. Better to build without KFW 70, save the money for the energy certificate inspection and the solar system (about 5,000), keep the insulation as is, and move on. Apparently, it’s not financially worthwhile.

Regarding the wall construction, another supplier told me the following:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: Yes, of course, we don’t list that separately because it’s required by DIN (German industrial standards).

Today, with our current supplier:
Me: Is there an air gap between the insulation on the masonry and the facing brick?
He: No, that’s a cavity insulation. That might have been necessary in the past, but with today’s insulation materials, it’s no longer needed.

So what is correct? Is an air gap between the insulation and masonry required by DIN, or does it depend on which insulation material is used?

I can only agree with that...

I would also build at least to KfW-70 standards again—but only based on the performance values, not because of the KfW funding... in my opinion, that funding is not worth it at all...

And you don’t necessarily have to build with solar panels and mechanical ventilation systems, but I personally wouldn’t want to do without our mechanical ventilation system. There are plenty of examples among neighbors and friends where people said, "Just open the windows," but recent experience shows that this is not quite sufficient—especially if you work full time...

Does "C" refer to the masonry work? Because those were two different contractors.
How do I find the right mechanical ventilation system for my house? Is mechanical ventilation always associated with unsightly covers, boxes, and housings inside the home?

Now, covers and valves, etc., are actually a different topic and not necessarily tied to the manufacturer of the system... there are also many that look quite good or rather unobtrusive...

For example, you can use a system from A, the piping from B, and the valves from C.

The offer states: "Supply air through ceiling or floor vents. Exhaust air through ceiling or wall vents."

Preferably on the upper floor, I imagine the floor vents like this: A metal plate with slots where all the dust from the room blows in and is very visible on the plate. Is that correct?

Yes, it looks something like that... however, nothing gets inside there because those are air vents... and the system should be running... so you have positive pressure at the outlet... dirt doesn’t get into a car tire either.

By the way, the offer only says that apples and pears are for sale... but the variety is not mentioned anywhere... and who buys apples and pears without knowing the variety? I would definitely ask the seller what exactly they are offering here... maybe I don’t even like that variety.