Fans don't improve comfort as much if humidity is high, because the airflow doesn't cause as much evaporative cooling on the skin. So you need a temperature gra

Fans don't improve comfort as much if humidity is high, because the airflow doesn't cause as much evaporative cooling on the skin. So you need a temperature gradient to get a good effect. Attic fans are a good example. The attic tends to get hotter than the outside air when the sun is shining, and the fan helps equalize.