Mechanical ventilation is powered by fans. Fans can be installed directly in windows or walls, or they can be positioned in air ducts to supply or exhaust air from a room.
The type of mechanical ventilation employed is determined by the climate. In warm and humid areas, for example, infiltration may need to be minimised or prevented in order to limit interstitial condensation (which occurs when warm, moist air from inside a structure penetrates a wall, roof, or floor and comes into contact with a cold surface). A positive pressure mechanical ventilation system is frequently employed in these situations. In cold areas, however, exfiltration must be avoided to limit interstitial condensation, and negative pressure ventilation is used. In a place where pollutants are produced locally, such as a bathroom, toilet, or kitchen, the
