Mixing ridge, gable and powered attic vents.
Installing and using a powered attic roof ventilator to ventilate an attic space is often regarded as poor practice by some roofing contractors.
Their reasoning is the same as that when they advise to close the gable end vents when installing ridge vents. The powered attic fan will “short circuit” the ventilation system by drawing air from the closest source of air, which would be the ridge vent. They assume that because the ridge vent is closer, it is also the path of least resistance for airflow. And they assume that the force of the attic fans’ volume is great enough to pull not only air, but outside weather elements such as rain, snow and debris into the attic.
Read more: Roof Ventilation | Powered Attic Fans