The study of fluid dynamics applied to ventilation systems has traditionally relied on experimental work and simulations using Reynolds-Averaged Navier-Stokes (RANS) computational solvers. With the advent of more powerful computers, it is now feasible to implement more accurate simulation methods, such as Direct Numerical Simulations (DNS), which can fully resolve turbulent plumes from heat-emitting bodies, offering a more precise understanding of airflow. In this work, we use DNS to simulate the ventilation of a single room with one or two heat-emitting bodies. We use several metrics, such as local air age and local temperature, to analyze the effectiveness of air circulation within the room and to identify ventilation short circuits and potential stagnation zones. Additionally, we modify the inlet air speed to assess the relevance of stack and forced ventilation in these configurations, and identify possible stagnation zones. We show that the presence of a second body does not modify the flow significantly, in accordance with previous results. This study demonstrates that advanced simulation techniques can lead to more efficient and effective ventilation solutions in buildings.