Vortex 347 CFM S Line S-600 Fan, 6" The s-line is a revolutionary series of fans that combine energy efficiency, ultra-quiet operations and a collection of advanced technologies that deliver unparalleled performances. An extremely energy efficient ac brushless motor powers the patented mixed-flow dual impellers. Built with double insulated walls, noise is reduced to levels that were previously thought to be unattainable. All s-line models are assembled with high impact resistant polycarbonate casings, an integrated back draft damper and a mounting bracket designed for quick and easy installation.