Ventilation is one of the most overworked words in engineering technology with its meaning having undergone many changes with the passage of time. It even now carries conflicting connotations to different individuals. Much has been written about ventilation, including a recent history which called attention to the changing patterns of ventilation practices. In this paper it is our intention to consider that ventilation is the circulation or passage of an air supply through an enclosure resulting in the displacement of some or all of the air contained in that enclosure by the supply air. Depending on the character and condition of the supply air it can dilute or change the quality of the air in an enclosure as well as alter its temperature and humidity. A mathematical analysis of the ventilation process appears later in this paper.