Which conditions are necessary for air flow to occur?

• A. A pressure difference and a physical connection between spaces.
• B. Only a temperature difference is required.
• C. A moisture gradient alone is sufficient.
• D. High wind with no connection.

Answer: (A)

Air flow between spaces happens when air is pushed from a higher-pressure area to a lower-pressure area, and there must be a path for that air to move. The pressure difference provides the driving force, while a physical opening or connection between the spaces gives the channel for air to travel through. Temperature differences can cause buoyant motions, but they don’t guarantee sustained flow unless a pressure gradient and a passage exist. Moisture gradients don’t drive bulk air movement, and even strong wind won’t move air between spaces if there’s no opening to provide a path. So the needed conditions are a pressure difference and a physical connection between the spaces.