Achieve KFW 70 with gas boiler + solar?

Hello dear forum community,

we are building a KfW 70 house and have already decided in advance - with our landscape gardener - on a geothermal heating system. However, our property is located in a water protection area and, as a precaution, we had a gas boiler with a collector field included in the contract as an alternative option. Now, after a more detailed review by the water protection authority, it turned out that we are not allowed to install our geothermal system there after all. Ok, we thought... we’ll just take the gas boiler, but then the architect from our house building company called us and informed us that this would not be possible with KfW 70, since 5 m² of collector area would not be sufficient to achieve the required share of 30% own energy for the heating system - we would now have to switch to an air/heat pump from the company Heliotherm and even have to pay an additional €500! I looked into the system on the internet but cannot get used to the huge outdoor air evaporator at all. What are the experiences with such systems? Supposedly I would not need an additional heating rod for this system, which ultimately causes high electricity costs with such a system? Does anyone have experience regarding electricity consumption? The system is called Heliotherm Basic Line air/heat pump! Please respond! Thanks

Hello,

....Ok, we thought... let's just take the gas boiler, but then the architect from our house building company called us and told us that this would not be possible with KFW 70,...

How does she come to that conclusion?
Apart from that, I would refrain from a solar thermal system if gas condensing boiler is set as the heat generator and rather insulate better (15% rule).

....- we would now have to switch to an air/heat pump from the company Heliotherm and even pay an extra 500€!

Why exactly this one? If air heat pump, it should have full modulation capability.
First, have it proven that an air heat pump is suitable for the project/location at all.

....
I have been looking into the system on the internet, but I just can't get used to the huge outdoor air evaporator.

With split units, only the evaporator is outside.

....What are the experiences with such systems?

Other people's experiences will hardly help, because every building project is specific.
What makes sense in A is barely acceptable in B and leads to a money pit in C!

....Apparently, I would not need an additional electric heating rod for this system, which ultimately causes high electricity costs with such a system?

What a spectacular nonsense! A certain share of electric heating rod is even necessary if it is to be economical overall. This applies especially to non-fully modulating air heat pumps.
Regards,
NB: These are the disadvantages when you get involved with a general contractor without contractually agreeing on sufficient dimensioning! Usually, things are estimated, assumed, guessed, and cobbled together depending on which representative just dropped by, instead of planning and dimensioning precisely! Often a money pit overall.

Ok, we thought... we'll just take the gas boiler, but then the architect from our construction company called us and told us that this would not be possible with KFW 70, because 5 m2 collector area would not be enough to achieve the required 30% self-generated energy share for the heating system - we would now have to switch to an air/water heat pump from the company Heliotherm and that with an additional payment of €500!

Normally I prefer to leave the answers to energy-related topics to €uro - but your architect's statement is utter nonsense! It is true that with only 5 sqm collector area you will not reach KfW 70 - it also depends on the location of the property relative to the sun - but in principle KfW 70 with gas condensing boiler and solar as well as more insulation is very well possible. Don't get me wrong - a reasonably dimensioned air-water heat pump is not the worst heat generator. BUT as the builder you should decide yourself which heat generator you want to choose. Your architect's statement - if said exactly like that - is an absolute "no go". Are you sure that she is actually an architect? Kind regards