The Contact Theatre, Manchester by Short & Associates is a very good example of passive ventilation. The principle behind the mechanically assisted natural ventilation system of the Contact Theatre is quite simple. External cool air is brought in through a series of ground level vents which are fed to under the seating. As the air heats up is rises but the extraction is through constructed H Pots above the theatre. These H Pots create a negative pressure from cross winds to suck the air out, however this is sometimes assisted by mechanically by fans in the base of the stack. Above is a sketch showing the passive of air through the main theatre space.