Can a gas condensing boiler be built to KFW-55 standard?

We also decided on gas + solar + ventilation to achieve KfW 55. Regardless of KfW, we would have chosen this combination anyway. Our municipality had gas installed in this new development area. Additionally, we did not want an external heat pump exposed to the weather. Deep drilling is not allowed for us. Therefore, the only remaining solution was with gas. Whether heat pump or gas, opinions differ. Everyone has their own view. However, gas should not be fundamentally demonized here.

Can you say something about the additional cost? Recently, the general contractor said without checking thoroughly that the 3-way combination of gas, solar, and ventilation is about 15k more than the air-water heat pump alone...

Can you say something about the surcharge? Recently the general contractor said without checking precisely that the 3-combo gas, solar, and ventilation is about 15k above the air-water heat pump alone...

Solar + central ventilation with heat recovery are at 15k and gas is included in the standard, air-water heat pump alone is at 16k + ventilation for 10k.

I have already dealt with this, we would rather have a gas boiler to avoid the dreadful box in the garden.... GU 1 says it doesn't work with KW55 and doesn't do it at all... GU 2 says it works easily if combined with solar thermal and with ventilation and heat recovery, price-wise then similar to a heat pump... I don't know what's true.... GD

Then get yourself a ground source heat pump with surface collectors (we are doing that too). It is more efficient than an air-water heat pump and you don't have the ugly device. Furthermore, if you get a photovoltaic system, you can operate the brine-water heat pump with it (except in winter, because not much electricity is generated then). Gas is getting more expensive. You produce a large part of the electricity yourself. Despite the gas line in front of the property, we decided against a gas boiler. Furthermore, you still have to (if not already done) lay the gas line onto the property. That also costs several thousand euros; have you factored that in as well?

We don't have gas here, unfortunately, so we have an air-to-water heat pump. To set it up properly, you need a lot of time and motivation to read through the web or you need a good technician... which is unfortunately very rare. Gas works, gas heats, gas is cheap. I just don't know what is supposed to be so cool about the air-to-water heat pump UNLESS you have [a photovoltaic system] with it, but you need to have the money for that first.