ᐅ How much buffer tank capacity is necessary?

Hello dear experts!

I am a complete beginner 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 building project. We are a household of 5 people and will be getting a brine-to-water ground source heat pump (boreholes 2 x 80m (260 feet)). Since we have chosen a bathtub with a capacity of 295 liters (78 gallons), we are supposed to have a buffer tank of 370 liters (98 gallons). However, I think the bathtub is never filled completely, and a person also takes up some space ;-) Wouldn’t a 300-liter (79 gallons) buffer tank be sufficient in this case? Could you please answer my question like this? Best regards

Thick insulation is definitely enough. You don’t even fill the tub fully, and you rarely bathe at 45–48 degrees Celsius (113–118 °F), meaning the hot water is still mixed with cold water.

It depends on the specific circumstances. The tanks rarely reach the full temperature, and during the coldest part of winter, it might not be sufficient. This is based on the experience of my neighbors with large tanks and 300L (79 gallons) storage.

Bullerbü2020 schrieb:

should we get a 370 l (98 gallons) buffer tank

which in 99% of cases has nothing to do with domestic hot water, but is intended as a buffer tank for the underfloor heating. As is well known, that is more redundant than useful.

So first clarify: Are we talking about the hot water storage for 5 people and a "party bathtub," or the buffer tank for the underfloor heating?

300 l (79 gallons) for 5 people would be fine, but a buffer tank for the underfloor heating is not necessary. In that case, the size doesn’t really matter.

driver55 schrieb:

Which 99% has nothing to do with domestic hot water but is intended as a buffer tank for the underfloor heating.

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

If there is only one storage tank, without a fresh water station or similar, it only makes sense for domestic hot water.

driver55 schrieb:

Which has 99% nothing to do with the domestic hot water but is meant to serve as a buffer tank for the underfloor heating.

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