190l vs. 309l hot water storage tank for 4 people

Good morning everyone!

For the construction of our single-family house (the shell is currently underway), we are currently awarding the heating and plumbing work. First of all, here are some key data about the building:

- 2 full floors, a total of approx. 180 m² (170 m² living space, 10 m² technical room)
- no basement
- gable roof
- KFW 55 EE (including air-to-water heat pump, photovoltaic system)
- it will be occupied by 2 adults and 1 child (later a total of 2 children)

Planned is an air-to-water heat pump in combination with a photovoltaic system as well as underfloor heating.

Supplier A offers the following for the air-to-water heat pump:
Brand Vaillant with a hot water tank of 190 liters and all necessary accessories + installation for 28,560.00 euros net.

Supplier B offers the following:
Brand Weishaupt with a hot water tank of 309 liters and all necessary accessories + installation for 22,628.20 euros net.

My question: Do you have experience with the size of the hot water tank? Supplier A says that 190 liters is sufficient for a 4-person household. It should be mentioned that we like to shower longer. So we are not necessarily the most economical in this regard.

Thank you in advance for your opinions/experiences.

I would definitely tend towards the 300L storage. 2-3 good showers and 190L is gone. Especially since the 300L ones are also significantly cheaper….

My question: Do you have experience with the size of the hot water tank? Provider A says that 190 liters is sufficient for a 4-person household. It should be noted that we like to shower longer. So we are not necessarily the most economical in this regard.

Provider A is wrong. Own experience with three children (and me as a part-time dad). When the three kids come back from the stable and shower (long hair requires a lot of water under the rain shower) the 300-liter tank is down to only 25-30 degrees. For me, only lukewarm water remains ;). Definitely install 300 liters.

Good morning everyone!

For the construction of our single-family house (shell is currently underway), we are currently awarding the heating and sanitary work.
First of all, here are some key data about the building:

- 2 full floors, total approx. 180 m² (170 m² living space, 10 m² technical room)
- not basemented
- gable roof
- KfW 55 EE (including air-water heat pump, photovoltaic system)
- it will be occupied by 2 adults and 1 child (later a total of 2 children)

The plan is therefore an air-water heat pump in combination with a photovoltaic system as well as underfloor heating.

Provider A offers the following for the air-water heat pump:
Brand VAILLANT with a 190-liter hot water storage tank and all necessary accessories + installation for 28,560.00 euros net.

Provider B offers the following:
Brand Weishaupt with a 309-liter hot water storage tank and all necessary accessories + installation for 22,628.20 euros net.

My question: Do you have experience with the size of the hot water storage tank? Provider A says that 190 liters is sufficient for a 4-person household. It should be noted that we like to shower for a long time. So we are not exactly the most economical in this respect.

Thanks in advance for your opinions/experiences.

We only have 150 liters for 3 people and I like to shower for a long time. That has always been enough so far. Also for a full bath and then a short shower afterwards. But: we have a gas boiler that can refill the hot water tank with 15 kW power! Your heat pump, on the other hand, will have a significantly lower output depending on the water temperature.

If you fill a somewhat larger bathtub with 240 liters and the air-water heat pump even heats to 55°, you already need a 160-liter tank and 80 liters of cold water for 240 liters of bath water at 40 degrees. And the air-water heat pump will then only be able to slowly reheat the tank, probably only with about 3 to 5 kW at this temperature level, i.e. a thin trickle. By comparison: an electric instantaneous water heater typically has a power of 22 kW and can therefore supply a shower "in real time" (although not a rain shower with very high water volume).

With 190 liters you therefore only have reserves for one full bath or about 15 minutes of showering (15x16 liters/min water at 40°). Anyone who comes into the bathroom afterwards will therefore have either lukewarm water or has to wait for hours.

Or everyone just showers briefly.

309 liters thus offers significantly more reserves (i.e., a full bath plus 15 minutes of showering next door) at the cost of slightly higher standby losses.

Good morning everyone!

For the construction of our single-family house (shell construction is currently underway), we are currently awarding the heating and sanitary work.
First of all, here are the key data about the building:

- 2 full floors, a total of approx. 180 m² (170 m² living space, 10 m² technical room)
- no basement
- gable roof
- KfW 55 EE (among other things, air-water heat pump, photovoltaic system)
- it will be inhabited by 2 adults and 1 child (later a total of 2 children)

The plan is therefore an air-water heat pump in combination with a photovoltaic system as well as underfloor heating.

Provider A offers the following for the air-water heat pump:
Brand VAILLANT with a hot water storage tank of 190 liters and all necessary accessories + installation for 28,560.00 euros net.

Provider B offers the following:
Brand Weishaupt with a hot water storage tank of 309 liters and all necessary accessories + installation for 22,628.20 euros net.

My question: Do you have any experience regarding the size of the hot water storage tank? Provider A says that 190 liters is sufficient for a 4-person household. It should be mentioned that we like to shower longer. So we are not necessarily the most economical in this regard.

Thank you in advance for your opinions/experiences.

I would also take the offer with the larger storage tank. Because heating the water with a heat pump does not happen as quickly as with a gas heating system.
If several people shower one after the other, there is enough warm water available.

Heating 200 liters can take 1 hour with an air-water heat pump.

Do you have any experience with the size of the hot water tank? Provider A says that 190 liters is enough for a 4-person household.

Take the 300-liter tank!
It could get out of hand for you :) Annoying if the quality of life suffers because of it. In the old house, we had 80 liters: one would be doing the dishes while the other was lying in the 170 cm tub, covered only with warm water.

It should be said that we like to shower longer.