What type of aircraft is a hot-air balloon classified as?

A hot-air balloon is classified as an aerostat, an aircraft that stays aloft primarily through buoyancy rather than aerodynamic lift.

The word aerostat combines the ideas of air and standing still. Hot air inside the balloon is less dense than the cooler surrounding atmosphere, creating an upward buoyant force. The envelope, basket, burner, and other equipment are all part of the aerostatic aircraft system.

Aerostats include both balloons and airships. A balloon has no engine-driven means of horizontal propulsion, while an airship has propulsion and steering systems. This distinction is why a powered dirigible is not simply another name for a hot-air balloon.

Hot-air balloons can control their height by heating the air or allowing it to cool, but pilots generally use wind at different altitudes to choose their direction. That makes them aerostatic aircraft, even when they travel long distances.