The vents (synonyms: ventilation systems, air ducts) are an interconnected maze of ducts and shafts that allow for the passage of air throughout a structure. They are often used by characters to move from room to room or to spy from. They may lead to the rooftops, to maintenance rooms, to elevator shafts, to secured rooms, or to other locations within a building. They may contain vertical shafts, large fans, and ventilation grates. They are home to aliens, small children, secret agents, and John McClane.

When designing ventilation systems consider which rooms they connect, how easy or difficult they are to transit, and why they were built large enough for a person to fit inside them.

What happens when the vents are shut off?

Ventilation systems are one way of distributing poisonous or hazardous gas throughout a structure.