By Mark van der Feyst
The positive pressure fan will provide ventilation by pressurizing the inside of the structure and pushing smoke and hot gases out. Smoke likes to live in low-pressure zones and when a structure is made to be a high-pressure zone, the smoke will seek out low-pressure areas.
In order for it to work effectively, there needs to be an opening and an exit. The opening can be a door or a window with the exit being of equal size or larger to accommodate the volumes of smoke and hot gases exiting the structure. Having more than one opening or exit will only compromise the operation and effectiveness of the fan. The structure will not be able to become a high-pressure zone. In essence it becomes like a piece of Swiss cheese, full of holes. A common mistake is to introduce the fan once all windows have been taken out and all doors are open.