Outdoor air-to-water heat pump is smoking and steaming

Yes, it also works if you let it calculate. If you build something roughly by rule of thumb, of course it won’t turn out well. Just compare everything side by side. Investment, operating costs, etc. and don’t forget the interest, then compare over a 20-30 year period. Keep in mind that with the gas boiler you will probably only need one for the entire period, whereas with heat pumps it will be two if things go badly, or three. So? The modern devices no longer need electricity to pump the refrigerant back and forth? But that is the counterargument of every air conditioning opponent. It would be new to me that the phase changes in both directions now happen spontaneously.

Yes, it also works if you let it be calculated. If you just build something roughly, it of course can't turn out well. Just compare everything. Investment, operating costs, etc. and don't forget the interest, then compare over a 20-30 year period. Keep in mind that with the gas boiler you will probably only need one for the entire period, whereas with heat pumps it's more likely two, or in the worst case three.

Is the type of heating already important for the building application, or can that be clarified later?
I have an appointment with the architect next week.

Maybe someone should start a thread – comparison of heating types – boiler vs. heat pump.