**4. Conclusions**

The research was carried out on a group of 109 thermally improved residential buildings. The energy performance of these buildings was determined. The energy performance is based on the actual energy consumption for heating. The calculations were made for the state before and after thermal modernization. The specific sets of important variables characterizing the examined buildings have been identified. The variables were grouped into sets depending on the di fficulty of obtaining them. They were used to build a prognostic model based on the rough set theory (RST). The use of this method made it possible to quickly determine the energy saving potential for heating after the completion of the thermal renovation.

The following conclusions can be drawn from the analysis of the indicators' evaluation of the model for forecasting the final energy demand for heating after thermal improvement:


**Author Contributions:** Conceptualization, T.S.; software, T.S.; data curation, T.S.; investigation, T.S. and S.K.; methodology, T.S.; project administration, T.S. and S.K.; supervision, S.K.; writing—original draft, T.S. and S.K.; writing—reviewing and editing, S.K. and T.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was financed by the Ministry of Science and Higher Education of the Republic of Poland.

**Acknowledgments:** We are grateful to Sławomir Kurpaska from the University of Agriculture in Krakow, Poland, Faculty of Production and Power Engineering and Thomas G. Mathia from Laboratoire de Tribologie et Dynamique des Systèmes, École Centrale de Lyon, France for their valuable support during this research.

**Conflicts of Interest:** The authors declare no conflict of interest.
