Attic ventilation fans are a good investment when excessive attic heat forces air conditioning systems to work harder, driving up electricity bills. Extreme attic heat often causes damage to roofing felt and shingles. Attic fans that include humidistats also help control cold-weather humidity that can damage roofs.
The fans work properly only when they have sufficient ventilation in the roof. Fans require 1 square foot of venting space for every 300 square feet of attic space. Attic fans generally aren't necessary in newly constructed homes that have adequate ridge and soffit vents, because the vents naturally circulate air, according to the Northern Virginia Electric Cooperative.