This is an educational tool that suppose to help users to better understand the relations between building geometry, orientation, thermal insulation, solar heat gains, heating demand and more. There is no default value for heat recovery efficiency. This value depends on the building that you make the calculation for. Usually, this value should be around 50 %, but this value doesn't fit in all cases. For a better understanding of the product, check the help menu or contact the developer on the following mail address for further support : firstname.lastname@example.org.