Tri-Stack fans provide a cost-effective and energy saving means for pollution abatement, re-entrainment and odor control problems. Fans and systems are used at hundreds of facilities, serving as direct replacements for conventional centrifugal exhaust fans. Lightweight, modular construction with lower system pressures than conventional exhaust stack design, help provide a two year payback when used for centrifugal fan replacement. Fans are also available with special materials of construction and/or coatings for use in caustic, corrosive and other severe environments such as chemical processing and wastewater treatment facilities. They can handle exposure to such chemicals as nitric acid, fluorides and sulfuric acids.