Air inside the building collects heat, moisture and impurities and must be exhausted. The evaporative air conditioner (cooler) provides 100% outside air which must be relieved from the building. If the building is sealed, the effectiveness of the cooler(s) will be reduced. Mechanical extraction or even just leaving some doors or windows open helps remove unhealthy air from the indoor environment by supplying 100% fresh, filtered air. For this reason, evaporative air conditioners (coolers) are much healthier than refrigerated air conditioning.