Powered attic ventilators. Sometimes referred to as attic fans, PAVs come in several forms. Some are designed to be mounted on the roof, while others mount in the attic floor or the gable end. All PAVs contain an electrically powered fan (usually controlled by a thermostat) that exhausts hot air from the attic on hot summer days. A PAV should not be necessary if a roof has properly sized and installed ridge and soffit vents. While a PAV will definitely exhaust hot air from the attic during hot weather, it consumes electricity, and can actually suck cooled air from the living space through leaks in the attic floor. For this reason, many home energy experts recommend passive roof ventilation over active ventilation with a PAV.
Installed along the roof peak, ridge vents are probably the most important vents in any "passive" (non-electric) roof ventilation system. Hot air that accumulates inside the attic rises by convection and escapes outside through ridge vents.
As hot air escapes, fresh outside air is drawn into the attic through soffit vents (see below).
On an asphalt shingle roof, ridge vents are usually covered by a layer of shingles. The warmest air in the attic rises naturally to the roof peak and escapes outside through the ridge vents.
Soffit vents run parallel to the eaves along the soffit. These vents work with ridge and gable vents to promote good roof ventilation.
Installed along the eaves of the roof, these vents are usually in the form of grilles that run the length of each soffit.
By admitting outside air into the attic as warmer air leaves the attic through higher vents, soffit vents play a major role in effective roof ventilation.
Installed near the peak of a gable end, this screened vent can allow hot air to leave the attic or fresh air to enter, depending on prevailing breezes and temperature conditions.