Several factors must be taken into consideration in selecting the proper ventilator for any specific problem:
? Mean temperature difference
? Stack height (chimney effect)
? Induction effect of the wind
? Area of ventilator opening
Of several other minor factors, only one requires close attention. This is the area of the inlet air openings (Fig. 3-4). The action of a roof ventilator is to let air escape from the top of a building, which naturally means that a like amount of air must be admitted to the building to take the place of the air exhausted. The nature, size, and location of these inlet openings are of importance in determining the effectiveness of the ventilating system.
