ᐅ How would you decide? Heat pump and plumbing offer from Viessmann

The Starting Point
We are currently building a semi-detached house in Baden-Württemberg and have received a comprehensive quote for heating, plumbing, and rough-in installation from a local plumbing and heating contractor. They work exclusively with Viessmann and want to provide us with a one-stop solution.

Our House Details
Project: New build semi-detached house
Living area: 205 m² (KfW-40)
Heating circuit temperature: 35/28°C (floor heating)
Heating energy demand: ~4,077 kWh/year
Domestic hot water demand: ~2,258 kWh/year
Household size: 4 persons (2 adults, 2 children)
Photovoltaic system: 8.39 kWp

The Plumber’s Offer
They are offering the Vitocal 222-S with an integrated 190-liter (50 gallons) storage tank (approx. €14,000 net), including installation.
When asked about a version with a larger, separate 300-liter (79 gallons) tank, they quoted an additional €8,000 net due to increased material and installation costs.

My Questions:

• The 222-S with 190 liters appears to be an older model (currently, the official website lists a 230-liter version).
• The surcharge for the separate 300-liter tank seems very high to me.
• He supposedly "does not negotiate" because he already has enough jobs (according to the site manager) – he is still the cheapest overall.

My Thoughts
I am uncertain how to evaluate this:
Is it common for contractors to offer older model versions?
Should I accept the 190-liter model (is it sufficient for 4 people)?
Is the high surcharge for the alternative a sign that he wants to push me toward the standard option?
Or is he simply a tradesperson with a set pricing structure who does not negotiate?

My Question to You
How do you assess the recommended heat pump, and how would you proceed in this situation? I have a comparison offer of the same scope with a 400-liter (106 gallons) tank that is overall €4,000 gross more expensive.

1. Who does such a standard, off-the-shelf sizing of the heat pump? A disaster... For KfW 40 standard, supply temperatures should be no more than 30°C (86°F) for a room temperature of 22°C (72°F).
2. Is there a floor heating installation plan prepared?
3. 190 liters (50 gallons) for four people is usually too little. Four people cannot shower one after another with that capacity. Definitely 300 liters (80 gallons). The extra cost is outrageously high.

Gut feeling: We always do it this way, no matter what kind of house. Off-the-shelf, and the customer is not supposed to come with any special requests.

190 liters (50 gallons) is definitely too little if you also want to fill a bathtub. Or if 2-3 people shower one after another. Just calculate the flow rate of a small rain shower and multiply accordingly.

Definitely too small. We have the 230 model and are a household of three people (including one woman), and it’s just barely enough.

We recently installed a heat pump in our house, and it works well. However, there have already been two occasions when we needed the HVAC technician: once because of a rattling noise in winter, and another time due to a malfunction where the heating system switched to grid electricity—so it stayed warm, but more expensive.

The technology is good but still relatively new, so occasional "issues" can and will happen. Therefore, I recommend finding a technician you trust, who will also respond promptly when something goes wrong.

ateliersiegel schrieb:
The technology is good, but not very old yet.

I have to disappoint you there. The technology is already over 150 years old, and heat pumps have been produced in series as heating systems for about 50 years. As climate control and refrigerators, they have been produced in series for over 100 years.

The technology is fully mature. It’s just that the devices tend to overdo it with electronic features. In my opinion, Asian manufacturers are better positioned due to their experience with 120 million air conditioning units produced annually.