ᐅ What happens when the hot water tank is empty?

Hello everyone,
I have a house offer with a "Junkers ground source heat pump STM // including a 185-liter (50-gallon) hot water storage tank."
A bathtub requires about 300 liters (79 gallons) of water to fill.

After using the 185 liters (50 gallons), will I still have immediate hot water?

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

Of course, it depends on the model, but 300 liters (79 gallons) for a full bath is quite high. It will more likely be around 150-180 liters (40-47 gallons). In addition, you are storing hot water at temperatures of 45-50 degrees Celsius (113-122°F), meaning it will still be mixed during filling.

ARPcPro schrieb:

Do I still have immediate hot water after using the 185 liters (49 gallons)?

Only if you have an instantaneous water heater. Otherwise, no.

On average, bathtubs hold around 150 liters (40 gallons). Space-saving bathtubs often have a volume of less than 100 liters (26 gallons). Large bathtubs for two or more people can hold 280–350 liters (74–92 gallons) or more. Of course, the amount of water needed for a full bath varies depending on body size.

If someone has showered before, it becomes tight, especially if you have a heat pump, as the storage tank is operated at a maximum of 50°C (122°F).

ARPcPro schrieb:

A bathtub requires about 300 liters (79 gallons) of water to fill.

An average full bath needs around 180 liters (47 gallons) of hot water. Do you have an oversized tub or planning something different for bathing?

ARPcPro schrieb:

After using 185 liters (49 gallons), do I still have immediate hot water available?

No – not without additional equipment. A heat pump is an efficient but slow system.

ARPcPro schrieb:

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

It takes hours if you want the water temperature in the tub to be fully warmed from the storage tank.

If you keep the hot water temperature at 57 degrees Celsius (135°F) and want the water in the tub to be 38 degrees Celsius (100°F), you need about two-thirds of the full bath volume from the storage tank – for a 180-liter (47-gallon) full bath that’s 120 liters (32 gallons). This amount is enough for one full bath and a relatively short shower.