What are some of the things filled with hot air for it to function?

Hot air balloons are primarily filled with hot air to provide lift, as the heated air inside is less dense than the cooler air outside. Similarly, airships, or dirigibles, utilize hot air or lighter-than-air gases like helium to achieve buoyancy and float in the atmosphere. Additionally, certain types of heating systems, such as hot air furnaces, rely on heated air to distribute warmth throughout a space.