How much buffer storage is necessary?

Hello dear experts!

Unfortunately, I am an absolute layman in all areas of house construction, but I have been trying to educate myself here for a long time. Now I have the following question about our construction project. We are a household of 5 people and are supposed to get a brine-earth heat pump. (Bohrung 2 x 80m). Since we have chosen a bathtub with a capacity of 295 liters, we are supposed to get a buffer tank of 370 liters. However, I think you never fill the tub completely, and you yourself also take up space;-) So wouldn't 300 liters of buffer tank be sufficient? Can you answer my question like that? glg

Thick is definitely enough. You don't even fill the tub remotely full, and besides, you rarely bathe at 45-48 degrees, which means the hot water is still being mixed.

It depends on the exact circumstances. The tanks are also rarely completely at temperature and in the "deepest winter" it could well be that this is not enough. At least that is the experience of my neighbors with large tubs and 300L tanks.

should we get a buffer storage tank of 370 l

Which is 99% unrelated to the hot water, but is meant to serve as a buffer storage tank for the underfloor heating. Which is famously more useless than water, namely superfluous.

So first clarify: Are we talking here about the hot water storage for 5 people and "party tub" or the storage for the underfloor heating?

300 l for 5 people would be fine, a buffer storage tank for the underfloor heating is not needed. In that case, the size does not matter.

The one that is 99% unrelated to the domestic hot water, but is supposed to serve as a buffer tank for the underfloor heating.

So how is domestic hot water generated or stored with the heat pump if not via a tank?

If there is only one tank, no fresh water station etc., it only makes sense for hot water.

The one that 99% has nothing to do with the hot water, but is supposed to serve as a buffer tank for the underfloor heating.

Completely misinterpreted the initial information but yes, hypothetically a possibility, just unfortunately not the topic of the thread.