Sustainable Cost Allocation of Common Area Heat Consumption in Multi-Apartment Buildings: A Case Study of Prishtina

District heating provides efficient urban heating; however, sustainable cost allocation methods in multi-apartment buildings often require additional attention, especially in developing markets such as Prishtina, Kosovo. These systems often rely on flat-rate billing, and they fail to account for heat consumption in common areas. Consequently, not all heat entering the building is accounted for or billed. This leads to systemic cross-subsidization, penalizing energy-conscious consumers while allowing inactive or unoccupied units to benefit from unmetered heat transfer without contributing to the associated costs. To address this, this study proposes a coefficient-based economic allocation model to equitably distribute common area heating costs in mixed-metered buildings, thereby promoting sustainable energy consumption. Using Prishtina as a case study, the methodology determines an optimal common-heat coefficient (β) via constrained boundary analysis based on a physical constraint (net-to-gross area ratio of the building stock ≤ 27.5%) and an economic constraint (fixed charges ≤ 30%). The methodology was informed by a comprehensive dataset of 414 thermal substations provided by the district heating provider “Termokos” (covering 18,546 heating units during the 2024/2025 heating season), with Substation 277-UL presented as a field case study to demonstrate the practical application and validity of the model. The results show three findings: First, the optimal coefficient is established at β = 20%, satisfying both boundaries and showing that the attributed part of the heating consumption for the common area should not surpass this value. Second, the framework tackles cross-subsidization, reducing specific bills for regular, heat cost allocator-metered consumers by 21.7% compared to unmetered billing. Third, the model proposes a transparent approach to distribute common heat costs across the building community, ensuring equitable participation in shared thermal expenses of common areas. Hence, this research serves as a first step toward establishing equitable billing policies, maintaining energy balance, and fostering socio-economic and energy sustainability in the district heating industry.