Your attic requires natural ventilation, and a solar attic fan will help nature get the job done. On a summer day here in the San Joaquin Valley, attic temperatures can approach 150 degrees. That accumulated heat conducts through the ceiling into living spaces. It also saps coolness from air conditioning ducts routed through the attic. In winter, unventilated attics may accumulate water vapor rising from the living spaces below and provide a moist environment for mold and mildew. These unwanted particulates may later infiltrate your home, not to mention rotting the wood structure and degrading electrical wiring. Most existing home construction incorporates lower attic vent openings at the soffits — located under the eaves of the roof — and upper vents at the gables on either end of the roof. Natural ventilation depends upon the chimney effect of warm air rising out of the gable vents, pulling fresh air into the soffits.