ᐅ Gas heating system plus solar panels: additional storage tank?

Good morning everyone,

Living area 140m² (1,507 sq ft). Entirely underfloor heating, no basement.

I need some expert advice on this. I was offered the following:

Wolf gas condensing boiler CGB with standard storage tank CSW-120
+ domestic hot water solar system including a 200-liter (53-gallon) solar storage tank

I'm confused about the fact that there are two tanks. Is this normal? I always thought it would be a combined tank. Shouldn't the system "work and communicate" together? Is the storage tank large enough? (We are currently three people, and we plan to have one more child.)

Is the Wolf system good, or are there better options? (Vaillant/Buderus?)
Should the solar system ideally be from the same manufacturer?

Thanks for your answers and clarification.

Oh yes, it is a KfW 70 house.

Interesting... we are also building a KfW 70 house, with 182 sqm (1956 sq ft), and we were required to install a 750-liter (200-gallon) tank, which, as far as I understand, is used as a storage tank for hot water and heating support... however, I am not entirely convinced about the necessity of the 750 liters, so I will have it checked again to see if it is really required...

Wolli79 schrieb:
We are also planning to start thinking about building a house soon. Finally! 🙂

Then you should make sure to begin adequate planning and sizing of the system as soon as the building structure is defined.

Wolli79 schrieb:
...Are these additional storage tanks really necessary?

That depends on the system concept. For solar thermal systems used for domestic hot water, combined storage tanks are common. When using heating support (HS), having two separate tanks is more efficient than, for example, a tank-in-tank system (combined storage). However, with HS the risk of stagnation increases.

Overall, for a single-family home, it’s worth considering whether a solar thermal system truly represents an economical investment, as the optimistic calculations on paper rarely materialize in reality.

Kind regards,

Thank you very much for the support!