Diffuse ceiling ventilation (DCV) represents an innovative air distribution strategy that supplies air to a plenum before diffusion through suspended ceiling panels into occupied zones, offering potential advantages over conventional mixing ventilation (MV) in heating conditions. This study presents a comprehensive building energy simulation analysis comparing DCV and MV heating performance using EnergyPlus for an office room in Copenhagen. Five convective heat transfer coefficient (CHTC) algorithms and three thermal mass levels were considered. Multiple regression analysis quantified the relative importance of thermal mass levels and CHTC algorithms on system performance. Results demonstrate that DCV consistently outperforms MV across all scenarios, achieving energy savings of 1.3–2.1 kWh/m2 (5–9% reduction) and providing better thermal comfort, with a lower average predicted percentage of dissatisfied values during occupied hours (7.4% vs 8.9%). The analysis reveals that the thermal mass level primarily influences HVAC energy use in both systems, while the selection of the CHTC algorithm mainly affects peak heating demand and thermal comfort predictions. This research establishes DCV as a viable energy-efficient alternative to conventional MV systems in heating-dominated climates.