ᐅ Heat pump for 148 sqm KfW55 house

Dear heat pump experts and experienced home builders,

I would like to better understand what heat pump capacity we actually need.

Our project:
2 full floors
No basement
148 sqm (1,593 sq ft)
KFW55 standard

In our energy demand calculation, a 6 kW air-to-water heat pump is recommended.
However, the heating load calculation in the plan specifies an 8 kW air-to-air heat pump.
Both calculations seem to follow a standard procedure, as this is a developer project.
Which figures in both documents should I focus on?

To me, 8 kW seems quite high, but this is just a feeling formed by reading here in the forum.

The underfloor heating is already installed, also standard, and the screed has been curing for 4 weeks, waiting for the system to be heated up.
But there is no heat pump installed yet.
The builder would credit us €15,000 if we handle the purchase and installation of the heat pump ourselves.

All these questions are overwhelming us.
Is this even possible? Can we choose a different model or manufacturer?
Is it worthwhile, is €15,000 a reasonable amount?
Is 6 kW enough? ...
We need solid information to stand our ground with the builder.

Help!
Thanks!

So I wouldn’t recommend sourcing and installing the heat pump yourself. Any potential heating issues in the future will be blamed by the builder on the heat pump and its installation. Additionally, what happens if the heat pump suddenly becomes unavailable for you? That would be too risky for me.

Mono- or split-system – which one are you planning to install? What does the heating engineer usually install? Do you know anyone who could install the pump otherwise?
15,000 might be tight including installation; maybe you should try to approach it the other way around: you provide the pump, they install it and pay for the pump... or you agree on a compromise.

By the way, be careful—if you supply the pump, you are also responsible for its foundation... we had to learn that the hard way.

For now, we just want to explore all options and consider every direction.
We are planning to install a Daikin Altherma 3 R F split system.
Whether someone will install it for us still needs to be clarified. We are also aware of the warranty issues, which are not ideal. The developer is quite easily getting out of trouble with this option and shifting the responsibility onto us.

@Reggert
Are you referring to the foundation for the indoor unit or the outdoor unit?
Inside, we already have a screed floor, so I’m not sure if anything special is planned for that. We intended to handle the foundation for the outdoor unit ourselves anyway.

Exactly outside

Hmm, first find someone who installs the heating system, otherwise you’ll end up with nobody doing it.