An attic fan doesn’t typically lower the energy bill by much, if at all. The energy savings they provide is typically countered by the energy they use. Attic temperatures can reach up to 150 degrees Fahrenheit in mild to hot climates, and fans pull hot air outside to reduce the temperature.  However, they do: Reduce the strain on your AC. Reduce humidity in the attic. Help protect roofs from extreme heat.  They may provide more benefit in mild climates as they only use 10%–15% of the power of a traditional AC.