Powered Attic Ventilators (PAVs) are ineffective and inefficient, despite what you may have heard. There are a couple of significant problems with theses types of attic fans. First, the only way a PAV pays for itself is if a house has problems with ceiling insulation or attic venting. Cooling only happens because conditioned air is simply being drawn up from the house downstairs. The fans aren’t really cooling anything; they are just blowing air around and using energy to do it. Second, PAVs don’t address the radiant heat created in attics. A fan just blows air over overheated attic materials, pushing that air down into the house. A radiant barrier would prove more effective.
Read the full article here: The Top Two Reasons Powered Attic Ventilators Are a Waste of Money | GreenBuildingAdvisor.com