KFW70 or KFW55 experiences?

@€uro

well, then install an air source heat pump with their annual performance factor in old buildings with inefficient building envelopes and later explain the point when the meter spins.

If it is planned properly, there is no problem at all. Then no meter will spin. An annual performance factor results not only from the air source heat pump but from the interaction of this with the entire system!

regards

well, it may be right for the wallet, the question is just for whom

of course, you can also sell an unnecessary ventilation system, at least then you save on heat recovery with an inefficient building envelope.

although, such a nice counterflow-layer heat exchanger in the garden of an old villa as modern plastic