It's not easy to estimate the amount of humidity that an evaporative cooler adds to the air in a space, because it depends on so many factors, including the temperature and humidity of the environment and the rate of exhaust ventilation. Evaporative coolers add humidity to air as they cool it, but some of this moisture escapes as air is ventilated from the space. One manufacturer estimates that using evaporative cooling in an appropriately ventilated space will increase the humidity about 2% to 5%.