ᐅ It takes a long time for hot water to arrive.

I’m generally not against tankless water heaters. They save on hot water piping, circulation lines (installation like additional piping), hygienic aspects, costs, and losses related to storage tanks. And so on.

It takes many years of significant hot water use from the tap for the higher investment in a central hot water system to pay off. But this decision is actually made for us by the regulators.

A heat pump with an annual performance factor (seasonal coefficient of performance) of 4 or higher for hot water? Even a ground-source heat pump rarely achieves that!

With an air-to-water heat pump, I get an average annual coefficient of performance of about 3.5 at 47°C (117°F).
I quickly estimated it for our consumption:
2000 kWh of hot water per year
equals 570 kWh of electricity per year
For instantaneous water heaters, assuming 20% loss compensation, it would be 1600 kWh of electricity

Calculation over 20 years:
Assuming an average electricity price of 35 cents

Cost difference:
(1600 kWh - 570 kWh) * $0.35 * 20 years = $7210
+ 4 instantaneous water heaters at $300 each = $8410

Additional centralized system costs: $600 for storage tank + $500 for small parts/piping = $1100

This results in about $415 extra costs per year for the instantaneous water heater. That would be approximately 35% more in electricity costs for us (heating and household electricity).

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

Your cost estimates are unrealistic. I want to see a hot water tank including labor under €1000, as well as piping for €500... I didn’t even get the circulation line for that price, which cost €1200 including the pump and labor.

Only for hot water; otherwise, I wouldn’t have mentioned it.
The tank, including installation, cost €600, and the pipework for the hot water lines for those few meters was about €500.
But I’m happy to repeat myself.
Well, I ordered the tank myself and placed it on a self-built foundation – so I probably saved around €400 there.
In my opinion, circulation is unnecessary.

Edit: Don’t forget that with tankless water heaters, you still have the hot water pipes inside the rooms; it only concerns the pipes leading to the rooms.

As mentioned, the 600 kWh includes the power consumption of the high-voltage pump. This pump runs whenever we turn on the cold water tap; otherwise, the water pressure would be too low, resulting in hardly more than a drip because there is almost no pressure from the public supply line.

It would be necessary to calculate exactly how many kWh this amounts to, but since it is a three-phase connection, it will definitely have some impact.

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

guckuck2 schrieb:

But the decision is already taken away from us by the legislator.

What do you mean by that? Instant water heaters are not banned, are they?

I’m considering installing an instant water heater for the shower in our second house that we will buy soon. Right now, there is a gas heating system with a hot water tank (standalone). The heating system is from 1985 and must definitely be replaced within 2 years. We visited the property two days ago. The basement, where the hot water tank was located, was steaming hot. I can’t imagine that being energy efficient.

My mother, who will live in the house, uses 20 cubic meters of water per year; let’s say half of that is hot water. That just can’t be economical, considering uninsulated pipes run over two floors and there are constantly 100 liters (26 gallons) of water at 60°C (140°F) in the basement kept warm.

The only downside is that the bathroom was recently renovated, and it bothers me to have to break it open again.

But you could also mount the instant water heater directly in the shower and just run the 50 cm (20 inches) pipe openly along the wall... If you use stainless steel, it won’t look so bad... Hmm.