2xWP and 3x ventilation in DH with granny flat necessary

Hello dear community,

I have already gathered so much information from the forum and therefore first of all many thanks for the many interesting and informative posts. Since I was not successful with the search, I will try it with a post here. Our house planning is in full swing and at the moment I am dealing with the first offer from a general contractor.

My children are building a semi-detached house on an existing plot in Munich, each with 130sqm, and a fully basement apartment with 45sqm. Now I have received the first offer from a general contractor and have the following questions:

[*]Are two air-to-water heat pumps always mandatory for KFW 55 and a total living area of around 300sqm? The building description lists heat pumps from Viessmann, Vaillant or Daikin (Rotex) to choose from. There is no heat demand calculation yet.
[*]The central ventilation system must be installed in triple execution. The arguments of the general contractor are the size of the entire living area, the three residential units, the high price and the required fire protection. It was not offered. On inquiry, a price of about €30,000 was mentioned.

I always thought that in a multi-family house/semi-detached house there is potential for savings through the shared use of the heat pump and ventilation.

Best regards
Ludwig

Are 2 air-water heat pumps always necessary for Kfw 55 and a total living area of about 300sqm?

No.

The central ventilation system must be installed in triple.

Must? No. Since these are two houses and one apartment, I would install separate systems for each house. The apartment then runs with one house. There, decentralized ventilation. Examples why I would do this: House 1 has a party with raclette and lots of grilled fish. I want to run the ventilation system at full power. House 2 is sick and annoyed by drafts. I want to turn the ventilation system down completely. House 2 should be sold but has no own heating. I wonder what that does to the purchase price. There are many more reasons. P.S. Large savings potential is probably not offered either, as the technology becomes more complex. Normally, for example, the two semi-detached houses are completely separated and decoupled from each other. You reconnect them with one ventilation system. Maybe then House 1 hears in the children's room through the ventilation duct what is going on in the bedroom of House 2...

Thank you for the quick response. How does the noise level behave? Do 2 heat pump outdoor units also mean a doubling of the volume, or does the noise level not increase?

How is the noise level? Do 2 heat pump outdoor units also mean a doubling of the volume, or does the noise level not increase?

That is a) subjective, b) dependent on the installation, and c) dependent on the device. Two outdoor units, each correctly selected according to the heating load and not always running at full capacity, are certainly quieter than one big beast that has a lot to do. The two small VW Golfs are quieter than the GTI, which roars loudly – figuratively speaking.

There are also large and quiet devices. But a separation of the technology is (as described by useful). 3 controlled residential ventilation systems is certainly not effective. 2 are more than enough. I suspect the general contractor usually builds "standard" and is now polishing the whole thing up to 300m3... We have more living space, a ventilation partially calculated 10 times above the standard, and manage with just one device.