Which type of air is denser?

Cooler air is denser than hotter air due to the behavior of air molecules at varying temperatures. When air is heated, the molecules gain energy and move faster, causing them to spread out. This increased molecular motion leads to a decrease in density because the same volume of hot air contains fewer air molecules as compared to an equal volume of cooler air, which is more compact.

In contrast, cooler air has molecules that move more slowly and are closer together, resulting in a higher density. This fundamental principle is crucial in various applications related to building performance and HVAC systems, as it impacts airflow and temperature stratification within spaces. Understanding air density helps professionals in the field assess ventilation strategies, control indoor air quality, and manage energy efficiency effectively.