Hybrid heating: Is a heat pump with a gas condensing boiler sensible in old buildings?

Hello everyone,

in a detached house with an attached garage and 145 sqm living space, an oil heating system is still installed, which is now to be replaced.

[*]The heating load is about 15 kW.
[*]The U-value of the facade is 0.97 W and double-glazed thermal insulation windows are installed.
[*]The roof is insulated.
[*]The top floor ceiling is insulated with 10 cm of rock wool.
[*]Furthermore, the house is fully basemented and the basement ceiling is insulated.

Does a heat pump with gas even make sense in an old building with such poor insulation? Or would it be more sensible to simply install the gas boiler? Does the heat pump even "kick in"? Or is the gas boiler always active then?
The advantage of the combination would be the higher subsidy. Subsidy with gas is only possible if solar thermal is installed, but that is not so sensible, right?

Does anyone have experience with the combination? What would you recommend? Or better first insulate everything new and then simply install the heat pump?

The energy consultant I had, who is also certified by KfW, is somehow completely clueless. So maybe someone here has a rough idea?

I wouldn't install 2 new heating systems. You have to purchase, maintain etc. both. I would also skip solar, unless the subsidy is very high. Pure heat pump is not sensible for the heating load either afaik

How did you determine the heating load? It seems very high to me.

Underfloor heating or radiators? For underfloor heating, which installation spacing? For radiators, which type?

I wouldn't install 2 new heating systems. You have to purchase, maintain etc. both. I would also skip solar unless the subsidy is very high. Pure heat pump is not sensible for the heating load either afaik

So, better just gas.

Underfloor heating or radiators? For underfloor heating, what laying distance? For radiators, which type?

No underfloor heating yet, but with a heat pump at least one would be installed downstairs then you could arrange the type and the laying distance accordingly, right?

I would leave out the gas heating, we are already dependent enough on that madman in Moscow, even if the political situation calms down again, economically it will probably never be like it used to be. I would generally distance myself from fossil fuels. If a combination, then maybe more with pellets or something, if it fits. Personally, I would rather try to continue investing in insulation/sealing and only run with a heat pump. But the heating load also seems very high to me, considering you have already done some work. Or is the house very large?