GAS / SOLAR or GAS / Ventilation + Heat Recovery

.... Does anyone have experience whether this (of course must be calculated).....

That's right, pure speculation, since it depends on the overall context in comparison to the respective reference building (Ht´, qp´´ ). So it makes absolutely no sense to try to compare individual U-values.

Best regards

Right, only the planner will probably be able to calculate that accordingly. But at the beginning, it was similar for me. The contractors really wanted to push solar on me. However, I insisted on an implementation without solar, only with gas and controlled residential ventilation/heat recovery, and made it clear to them that if they couldn't do that, then they were already out of the running. After that, at least 3 general contractors could offer it that way.

Feedback from me:

175 sqm city villa in timber frame construction (U-value exterior wall 0.14), triple glazing, no basement:

Gas condensing boiler WITHOUT solar, but controlled residential ventilation with heat recovery: achieving Kfw 70 is no problem.