KfW55 radiators + air-water heat pump or gas boiler?

So we thought about it normally... Underfloor heating is indeed an option. As you can see, we are still very undecided about the heating topic.

So would an lwwp + underfloor heating be the better solution? Means lower supply temperature, which is supposed to be good.

Additionally, we have planned a photovoltaic system... I can only roughly estimate the size at 5kwp, as the offer is not yet available.

I don't want two meters, so that we can also use the photovoltaic electricity for the air-water heat pump. We want to regulate that with little effort by simply always doing the hot water preparation between 2 pm and 4 pm, as the most photovoltaic power is expected at that time.

Do you think that will keep the electricity/heating costs within limits? You do read quite a few horror stories about it.

You first need a proper heating load calculation. After that, the overall concept will determine the heating capacity you need for the heating system. If a reasonably good standard is built, you will be under 5kW at design temperature. A heat pump combined with underfloor heating is practically ideal for this. And then a photovoltaic system to provide "free" hot water in the summer. This is just an idea of mine, but with the living area, an air-to-water heat pump will fit well as long as you don’t live in the Alps.

So would an air-to-water heat pump + underfloor heating then be the better solution?

I honestly consider radiators the worst solution and would go for underfloor heating. I know too little about alternatives like wall heating (or passive house). Let's say underfloor heating as a generic term for surface heating. Have the flow temperature designed as low as possible! How the heat is generated (oil, liquefied gas, wood/pellets, gas, air-to-water heat pump, ground source heat pump, ...?) is a separate decision. This can and should be decided independently of the underfloor heating. If money is no object and the conditions are good, I would choose the ground source heat pump with deep drilling (instead of surface collectors). So geothermal energy. For me, the next alternatives are gas and air-to-water heat pump. With gas you have the connection and the "chimney," with the air-to-water heat pump usually an outdoor unit (space, noise) and not arbitrarily hot water (ask your installer) as individual disadvantages.