The common problem: A client has excess humidity in the attic in the winter and excess heat in the summer. The client applies the logic that installing a fan will cool down the attic and remove the water vapor. This is an erroneous solution put forth by home improvement stores, as well as contractors and home inspectors who mean well but are not certified specialists.
So the question frequently posed to me by a homeowner is, “Should I, or should I not, install a gable vent exhaust fan in my attic?”
The answer is, almost never. In certain circumstances, where no other form of ventilation is feasible, I might consider it, but only after a complete evaluation of the home. The negative air pressure created by the fan can actually make the attic and house warmer, rather than cooler. The fan can draw warmer exhausting air down from the ridge upsetting natural air flow and causing the attic to get warmer. The fan can also pull air conditioned (cooler) air up from the living space causing the house to get warmer while removing the cooler air to the exterior. This causes the air conditioning system to run longer using more electricity, while the gable fan is running using, yup, even more electricity. How efficient or “green” is that? Not very.
Every home is different and requires an evaluation of the whole of its systems, rather than the parts. When your home was built and brand new it had a balanced system. Well-meaning homeowners may inadvertently upset that delicate balance in a number of ways. Adding more insulation, replacing the windows or upgrading the heating system can significantly alter the way a home operates. Unfortunately, the result of these good intentions is usually mold growth in the attic.