Why is attic ventilation so important?
The simple answer is that air in an improperly ventilated attic has nowhere to go, causing it to become stagnant and increase in temperature. As this hot air fills your attic, it heats up the insulation and the ductwork that is supposed to be carrying cool air throughout your house. Air in a well-ventilated attic stays cooler and, consequently, keeps your home cooler with less effort and energy.
The holes in the bottom are usually soffit vents, and if you're like 95% of homeowners your soffit vents are probably a mess - clogged, blocked, painted over, or entirely too small. Air will not leave the attic unless air enters, so check your soffit vents and clean them every couple of years. The holes in the top of your attic are generally ridge vents, wind turbines, static vents or power fans. If you want the air in your attic to move in the bottom and out the top, then you must provide the air with a definite path. Air will follow the path of least resistance.
So how do you ensure proper attic ventilation? Keep it simple! Air enters from the bottom through the soffit vents, and exits the top through the exhaust vents. Combine proper ventilation with a radiant barrier to drop surface temperatures of your attic insulation, and you will have an efficient attic that is cooler during summer weather and drier in the winter months.