Design of purchase contract with promised modifications by the seller

I would leave the point completely aside. The new heating system or the combination of the existing heating system and the new heating system should be coordinated with the house, including professional heating planning. You might also want to energetically renovate the house - the heating system will then be adjusted to the intended insulation standard of the house - these areas must definitely be planned together.

The condition should be evaluated by an expert in a real estate purchase consultation. In this, they also check the existing heating system including the underfloor heating for its consistency and further usability. Also in the area of building services engineering, improvisation and decisions based on intuition often take the place of professional planning.