Replace oil heating in a 60s house?

38 is still within the range. Do you heat all rooms fully for 24 hours? That is also important. The next step would be to replace the radiators with low-temperature radiators and/or activate them using fans. That also brings quite a bit. Without major effort, you can't turn an old building into a new one. But you can heat any old building economically with a heat pump if it hasn't been left to decay for 30-40 years.

Yes, I heat through. I also have typically wide old building windowsills that disrupt air circulation. That would be my next step, which could possibly bring 2/3 degrees of supply temperature. Changing radiators would be negligent, as that would have to be saved again first. I'm calculating quite sharply there. But I also currently have a moderate gas and electricity circuit. Personally, I expect an annual performance factor of 3 for myself. Let's see when I have to switch. It will probably be the 7kw Panasonic in a self-build then.

I can't reach 30 degrees flow temperature at +7 degrees outdoor temperature. More like 38.

And in "real" winter it’s 45…50 degrees. (It’s also not possible otherwise, if new buildings partly still calculate with 40 degrees.) The question is also, which return temperatures are we talking about?

But you can economically heat any old building with a heat pump, as long as it hasn’t been left to decay for 30-40 years.

Now let's get down to business... what is a well-maintained but not explicitly renovated old building for you? What is its heat demand and what flow temperature does it require? What average outside temperatures do you assume in the relevant heating months December-February? Otherwise, we are just arguing here with strawmen. I already gave my definition yesterday as well as the calculation that follows from it.

And with "real" winter it's 45...50 degrees. (It's not possible otherwise, since new buildings partly still calculate with 40 degrees.) The question is also, which RTs are we talking about?

I don't reach 50 degrees even at NAT. Even at -18 degrees I was still below 50 degrees flow temperature. As I said, radiators simply have a lower limit in terms of output at low flow temperatures. The solutions have already been mentioned. The return temperature is usually 4 degrees below the flow temperature. I run a high flow rate so that the gas heating cycles as little as possible. Currently I have 768 burner starts over 3708 burner hours. But I think we're getting off topic :-)

Room temperature is the question… Return flow doesn’t really matter.

At 7 AT 38 and at -18 not 50 :D

I have to go to the pool now… to cool down…