The aim of the study is to highlight an area of regulation of district heat suppliers that needs to be addressed in order to achieve sustainable, long-term, and safe operation. Fixed assets make up the largest proportion of the asset structure of companies carrying out district heating supply activities. In order to ensure sustainable, long-term, and safe operation it is important to replace these assets on a regular basis. According to my calculations though, in the period of the study the investment activity in the sector, considering the average age of the assets used in the district heating supply, was not satisfactory. The current regulatory and support system does not encourage replacement, improvements and modernization.