Explore the physics of hot air and its impact on building ventilation in this Royal Institution lecture by Director Shaun Fitzgerald. Discover how innovative research has revolutionized building ventilation systems, leading to significant energy usage reductions. Delve into topics such as mechanical ventilation schemes, principles of natural ventilation, maximizing displacement ventilation, and the use of water bath and CFD modeling. Examine case studies including the Birmingham Town Hall and Contact Theatre, and learn about hybrid designs incorporating both displacement and mixing ventilation strategies. Gain insights into recommended winter and summer ventilation strategies, and understand the potential for improving energy efficiency in buildings worldwide.