Attic ventilation systems effectively reduce heat and moisture in your attic, protecting your home from their damaging effects. In addition, they promote energy efficiency by reducing the load on your heating and air conditioning systems. They also reduce the risk of ice dams forming in areas of the country that have severe winter weather.
To explain it simply, exhaust ventilation systems allows hot, moist air to escape at or near the roof ridge. Moving air out of the attic through the exhaust ventilation system is done throw either passive systems that use offsetting intake ventilation systems to create a vacuum or an active or powered system that uses fans that run on an electrical source.