It takes a long time for hot water to come

I basically don’t find instantaneous water heaters stupid. The saved hot water piping, circulation line (installation like additional piping), hygienic aspects, costs and losses for the hot water storage tank. And so on and so forth. A lot of hot water has to come from the tap for many years in order for the additional investment in central hot water preparation to be worthwhile. But the legislator takes that decision away from us. Heat pump with a seasonal performance factor >=4 for hot water? Even a brine-water heat pump rarely manages that!

With an air-to-water heat pump, I come to about 3.5 on average per year at 47°C. I quickly calculated it for our consumption: 2000 kWh hot water per year equals 570 kWh electricity per year. Instantaneous water heater with an assumption of 20% loss compensation would be 1600 kWh electricity. Calculation over 20 years: assuming an average electricity price of 35 cents.

That makes: (1600 kWh - 570 kWh)*0.35 €*20 years = 7210 € + 4x instantaneous water heaters at 300 € = 8410 €.

Additional costs central: 600 € storage + 500 € small parts/piping = 1100 €.

That makes a total of 415 € additional costs per year for the instantaneous water heater. That would be about 35% more in electricity costs (heating and household electricity) for us.

3.5 only for hot water or mixed over the year including heating? I think the latter. Hot water with heat pump is less efficient due to the high temperature.

Your comparison costs are unrealistic. Hot water storage including labor under €1000, I want to see that, also piping €500... I didn't even get the circulation line for that, which cost €1200 including pump and labor.

Only for hot water, otherwise I wouldn't have written that. The storage tank cost 600€ including installation and the piping for the hot water for those few meters is about 500€. But I’m happy to repeat myself. Well, I ordered the storage tank myself and placed it on a self-built foundation – so I probably saved about 400€. Circulation is, in my opinion, useless. Edit: Don’t forget that with instantaneous water heaters you still have the hot water pipes in the rooms; it’s only about the pipes to the rooms.

As mentioned, the high-voltage pump is included in the 600 kWh. It also runs when we turn on the cold water; otherwise, the water pressure would simply be too low for more than a trickle to come out, as almost nothing comes from the public supply.
One would have to calculate how many kWh that is, but since it is a three-phase connection, it will definitely be a bit.

Edit: our house has no hot water pipes except for those from the tankless water heater to the consumer (1-2 meters).
There were also no heating pipes.

But the legislator takes the decision away from us.

What does that mean? Instant water heaters are not prohibited, right?

I'm thinking about installing an instant water heater for the shower in our soon-to-be-purchased second house as well. Currently, there is a gas heating system with a hot water tank (specifically mentioned). The heating system dates from '85 and must definitely be removed within 2 years. We were there for a viewing the day before yesterday. In the basement where the hot water tank was located, it was boiling warm. I can't imagine that is energy efficient.

My mother, who is supposed to live in the house, uses 20 cubic meters of water per year, let’s say half of it is hot water. That just isn’t economically viable when you have uninsulated pipes running over two floors and constantly 100 liters of water at 60° warm in the basement to maintain.

It’s just unfortunate that the bathroom has just been freshly renovated; it bothers me somehow if everything has to be torn open again now.

But you could also just hang the instant water heater directly in the shower and run the 50 cm of pipe over the wall... Just use stainless steel so it doesn’t look so sh****... Hm.