Construction costs are currently skyrocketing

You don't have to at all. If you mix your knowledge about, for example, heat pumps from headlines and general rejection, unfortunately, only hysteria remains.

Apart from that, we have already had "renovating the whole house" in recent decades, namely when switching from night storage heaters mostly to gas.

To add to that, I live in the Ruhr area, where people switched from coal stoves to gas/oil, possibly with the intermediate step of night storage heaters. So it seems to be possible as well.

The important thing is the topic of subsidies and the transition period.

Important is the topic of funding and the conversion period.

Exactly, and as far as I understand so far, the conversion period for everyone whose heating system is now at least 30 years old is only 2 or 3 years? Considering the delivery times and availability of craftsmen, does that basically mean starting immediately?!

There are already differences though. For night storage heaters, a thick power cable per heater is needed. That can be retrofitted quite easily. For radiators, pipes are needed, which is still manageable. Everything from coal stove to gas heating remains in the high-temperature range. For heat pumps, however, you have to go into the low-temperature range, and surface heating is required there. Underfloor heating is the most complex since the entire screed has to be removed; moreover, doors and sockets no longer fit. I now rather see ceiling heating there. But for low temperature to get warm, the building envelope must be appropriately upgraded. And that entails a whole series of consequences. On the other hand, you don’t want to operate a heat pump with a seasonal performance factor of 2.

Heat pumps can certainly be operated well without underfloor heating. But not with the radiators that are usually found in houses where the oil or gas heating system is correspondingly old. Or you couple the radiators with a water-bearing fireplace, which is also not inexpensive, and burning wood is no longer desired anyway.

I think it is clear from this discussion that Habeck’s confusion will never be approved as he planned. Old buildings need to be renovated, for sure! Possibly also with the goal of installing a heat pump (that’s how we do it), but that takes time, money, and must be done with sense and understanding. To me, it all seems extremely haphazard again, what our green philosopher is coming up with. Let’s see what the Hampelampel will make of it in the end…

I once had the topic with my parents. Their house is theoretically designed for storage heaters, but in practice it is heated with two wood stoves. However, they are now in their mid-60s, and making wood and constantly stoking the fire eventually becomes a burden. At the time, my father was quite optimistic about being able to retrofit radiators with little effort and wanted to hide the pipes behind the baseboards. Along with the fiber optic installation, a gas connection was even laid two years ago, which now seems to have been for nothing ;)

I strongly doubt that you can reach 65% with solar thermal. Even with optimistic calculations, it's simply not feasible