Ventilation includes both the exchange of air to the outside as well as circulation of air within the building.
It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Kitchens and bathrooms usually have exhaust fans to force air out. Ceiling fans and table or floor fans circulate air within a room for the purpose of reducing temperature by evaporating mist from wall or sweat from skin that absorbs significant amount of latent heat of evaporation. However, after a certain time when the indoor air saturates the ceiling or table fans flow of air provide little impact unless an amount of outdoor air is let in.