Natural ventilation is an important factor in the design of sustainable buildings; it has the potential to improve air quality, while providing thermal comfort at reduced energy costs. Computational fluid dynamics (CFD) simulations provide comprehensive information on the internal flow pattern and can be used as a design tool. The present work offers insight of natural ventilation in a fully functional building, namely, the solar facility Interlock House in Iowa. Ventilation in the house is studied during summer months with some of its furniture included. The results show quantitative agreement between numerical simulations and experiments of vertical temperature profiles for each room. The temperature profile of the room with the inlet opening shows a more pronounced temperature variation. Flow patterns show higher velocities near the walls and marked flow circulation towards the opposite side of the building. The purpose of this work is to validate the numerical model that predicts airflow distribution for different configurations.