What size hot water storage tank with heat pump?

I am currently wondering which size is more suitable for a single-family house with 4 people (without a bathtub)? 200l or to be on the safe side, 300l?

Guests aside - the typical scenario would be all 4 people showering in a short time in the morning. And another case: in summer, everyone taking a quick shower again after the outdoor pool in the evening.

With a water temperature in the storage tank of 50-55 degrees and showering at 35-38 degrees, the water is still "diluted" with cold water. Calculated, with 7 minutes of showering per person and 10l/min, there would be a demand of 280l of mixed water. If you then shower at 40 degrees and only have 50 degrees in the storage tank, it gets tight - 210l would be required.

Nevertheless, the difference to 300l seems quite large to me. How does it look in practice?

No one can give a general answer, it depends on you. I would go for 200l. But I also find 7 minutes per person very much. Even with my long hair, half of that is more than enough.

No one can give a blanket answer, it depends on you. I would go for 200l. But I also find 7 minutes per person very much. Even with my long hair, half the time is more than enough

The 7 minutes is more of an assumption with a potential teenager surcharge. So you would probably be fine with 200l – with 300l I would probably keep 100l warm for free most days of the year, and tend to increase the turnover times in the storage tank.

The problem with the teenager can also be solved by the parents showering first.

That really seems to be very individual. So for me, without a bathtub would already be a "does not compute," but each to their own. But 35°C shower temperature and 3.5 minutes including washing hair? Did you all go to the military junior school? We have 190 and are three people. We manage so that two can shower one after the other if the first one holds back. If I were you, I would go for 300l. If necessary, you can always lower the storage temperature so that it regularly runs out.

How does it look in practice?

Practice as a father of three teenage girls - with 200 liters we couldn't all shower one after the other. At least not in a way that the last of us would still have truly warm water - practice e.g. when all three girls come in from the barn (so on Mondays, Fridays, Saturdays, Sundays). I'd rather play it safe and size the hot water tank a bit larger and take 300 liters. And even then, if 3x long hair is showered extensively and also worked on with care products (which teenagers just need), it would be tight for me as the last showerer.