The increasing frequency of power outages, caused by severe weather events and the synchronization of the Baltic electricity grid with continental Europe, highlights the need for energy supply security. This is especially critical for residential buildings dependent on district heating (DH), which serves approximately 70% of apartment buildings in Estonia and over 80% in several Nordic cities. While cogeneration plants could provide DH network with heat by switching to “island mode” during blackouts, residential buildings typically lack backup generators, posing risks to uninterrupted heat supply. Research from Sweden found that natural circulation will occur in buildings’ heating systems, allowing limited heat distribution during power outages. The present study aims to validate and assess the reproducibility of these findings under Estonian building conditions. Two field tests were conducted based on the hypothesis that natural circulation will occur if the temperature difference between the secondary circuit’s supply and return water is sufficient. Results show that natural circulation can occur if primary valves remain open and sufficient temperature differences exist. Tests show other measures are needed to transfer heat from DH network to buildings during electrical grid blackout. This research proposes practical recommendations to support DH utilities and building owners in enhancing system resilience during blackouts.