Gas boiler without solar - from when is that allowed?

Hello everyone,

we are currently building a new house 220m² + 110m² basement, of which 80m² in the basement is heated. It is being built without KFW funding and currently without an energy consultant. Attic not developed. Brick 36.5 with 0.09 UW value, triple-glazed windows, roof 60mm wood fiberboard, collar beam insulated with 35cm mineral wool, also in the slope.

The house has a controlled residential ventilation system with heat recovery and geothermal exchanger.

So far, we had planned a gas boiler with solar thermal, which is not profitable when comparing the additional costs for the ST with the gas price. However, until now we believed that gas is only permissible in combination with ST. My question is now - is that correct?

Would it possibly be possible to install a pure gas boiler with precise calculation? My research so far has shown that especially due to the controlled residential ventilation, this might be permissible? However, I would rather not commission an energy consultant who then comes to the conclusion that it is not possible, since we could have saved the costs.

We are currently wavering between a pure gas boiler (if this is permissible) or a fuel cell due to the government subsidy. Gas + ST have been excluded.

Thank you very much and best regards

PS: No, there is no architect or general contractor taking care of this. Although it costs us a lot of time, it is currently working very well

So far, we have been under the impression that gas is only permissible in connection with ST. My question now is – is that correct?

No, it is fundamentally also possible with controlled residential ventilation. But the house must still comply with the Energy Saving Ordinance, and that must also be proven.

we are currently building a new building 220m² + 110m² basement, of which 80m² in the basement are heated.

...

PS: No, there is no architect or general contractor taking care of it. It costs us a lot of time but is currently working very well

I don't believe that you are already building. Because then you would have gone through an approval process that cannot be carried out without a heat protection certificate documenting the installed system technology. Also, this would have failed due to the absence of an authorized person for the building documents.

In this respect, regarding your P.S., the time has probably come when this no longer works very well.

However, controlled residential ventilation alone is usually not sufficient. Thus, it is basically controlled residential ventilation + additional compensatory measures.

And yes, I know for many controlled residential ventilation alone was enough, but then the house was already better positioned from the start due to other adjustments that had been made beforehand.

And yes, I know that for many, just the controlled residential ventilation was enough, but then the house was already better positioned from the start due to other adjustments that had been made beforehand.

Which would those be, for example? Something like thicker insulation under the floor slab, etc.?

Insulation measures, better basic equipment, lower primary energy demand andunuund.