What happens if the hot water tank is empty?

Hello people, I have a house offer with "Junkers ground source heat pump STM // with included 185 liter hot water storage tank." A bathtub requires about 300 liters of water to be filled. Do I still have immediate hot water after using the 185 liters? If not, how long does it take before I can continue filling the bathtub?

Of course, it depends on the model, but 300l for a full bath is still set exceptionally high. It will rather be 150-180l. In addition, you store hot water at temperatures of 45-50 degrees, i.e. it is still mixed during filling.

Do I still have hot water immediately after using up the 185 liters?

Only if you still have a tankless water heater. Otherwise not.

On average, bathtubs hold about 150 liters. Space-saving bathtubs often have a volume of less than 100 liters. Large bathtubs for 2 or more people hold 280 – 350 liters or more. For a full bath, of course, less water is needed depending on body size.

If someone has showered before, it gets tight, especially if you have a heat pump, you operate the storage tank at a maximum of 50 degrees

A bathtub needs about 300 liters of water to be filled.

An average full bath requires about 180 liters of warm water. Do you have a giant tub or are you planning to bathe in something else?

Do I still have hot water immediately after using the 185 liters?

No - not without additional technology. The heat pump is an economical and slow system.

If not, how long does it take before I can continue filling the bathtub?

That takes hours - if you want to have the full temperature from the storage tank in the tub.

If you keep the hot water temperature at 57 degrees and want water at 38 degrees in the tub, you need 2/3 of the amount for a full bath from the storage tank - for a 180l full bath that is 120l. Enough for a full bath and a not too extended shower.