Hello Gibson,
yes, that is correct, according to the state geothermal law, for existing residential buildings with an area of 50 square meters or more, ten percent of the energy demand for heating and hot water must be covered by the use of renewable energies (biomass, solar energy, geothermal energy, bio-oil, and biogas), provided the heating system is replaced.
In your case, since a heating system is present, I would also assume a replacement.
Exceptions to meeting the requirements exist only if
[*]other public-law regulations oppose compliance,
[*]implementation is technically impossible,
[*]the conversion represents an unreasonable hardship for the homeowner (e.g., if they do not have sufficient financial resources themselves), or
[*]renewable energies were already used before the law came into effect.
However, there is the regulation that the requirements only have to be met if the central heating system is replaced. Gas or oil floor-standing heaters are exempt from the provisions. This is now the detailed question that still needs to be considered to check whether the law applies to you.
And I am of the opinion that your wood stove can certainly be counted here, but this is also a detailed question, and you should contact an energy consultant who will prepare the energy certificate you need anyway, which you also need for proof and possible subsidies. But basically, the combination of the existing stove and a new gas heating system should meet the requirements.