Why does the gable-mount power fan have a 3-ring design shroud?

The open ring configuration of the gable-mount power fan allows the fan motor to move air more efficiently and with fewer restrictions.

Air Vent's gable-mount fan blades are encased in a patented series of rings, not a cylinder like traditional gable fans. This open ring configuration allows the fan motor to move air more efficiently and with fewer restrictions. As a result, the fan operates quieter and more efficiently than traditional units.