Heat pump - Domestic hot water preparation

If the bathtub has standard dimensions, for hygiene reasons use the smallest possible heat pump-compatible storage tank with a large heat exchanger of 2-3m2. 200 liters are more than enough for your needs, then the water doesn't stand for too long. Much smaller heat pump tanks are not available. I would try to avoid circulation. Alternative: fresh water station, in my opinion not necessary. But read up on Legionella and decide for yourself.

The OP just has to be aware that circulation consumes a lot of energy and should, if in doubt, only be activated during the main usage times. Depending on the distance between the bathroom and the heating room, I would possibly recommend one for comfort reasons.

The OP must be aware that a circulation really costs energy and should only be activated during the main usage times if in doubt. Depending on the distance between the bathroom and the heating room, I would possibly provide one for comfort reasons.

No, circulation will definitely not be used.

200 liters should be more than enough, I would even go with just 150 liters. I believe we currently have only 210 liters installed in the two-family house with 4 adults and 4 children.

You must not confuse that 210 liters of hot water storage are not always equal to 210 liters of hot water storage. Do you have gas and possibly solar thermal (ST) in your two-family house? Then the water is often 90° warm. With the heat pump, it is usually no more than 50°. That means your 210 liters could already correspond to 400 liters with a heat pump. 150 is way too little, that is enough for a single household or flow temperature if you shower at work, etc.

Gas is something different. Check your current daily consumption. If long showers and rain showers are involved in the long term or if showering and bathing occur directly one after the other, you can also consider over 300l. With a heat pump, the storage tank is initially cold when it is cold. The disadvantage of a large storage tank is that the water stands for a long time when demand is low, and that at hygienically not ideal temperatures.

The small storage tank can be pushed by higher temperature and more frequent charging, costs more electricity with high water demand than a large storage tank, but I personally prefer it for hygiene reasons.

The integrated tanks have 160-210l depending on the model and manufacturer. Recharging takes a while, so for the few occasions of visitors it can be tight. With a gas heater, it’s hardly comparable. Such a gas burner usually has over 10, 20kW. When it turns on, it makes hot water on demand.

Currently running at 50 °C in the hot water tank. But yes, it is gas. That's why only 200l for twice the number of people. That's why I think that 150 to 200l with a heat pump would be sufficient for us. I have already written something about showering and bathing behavior earlier. Simply not much hot water is needed for us.


Thanks for the hint, I will take it into account. And your other statement fits with what I have written.