Sizes Available: 6 feet to 40 feet (1800 mm 12000 mm) in diameter Heights Available: Up to 18 feet (5400 mm) Operating temperature range: 20C to +65C (4F to + 149F) Galvanized Steel Stainless Steel fasteners Parag Fan Stacks have been designed for the greatest thermal efficiency, as well as superior strength. The parabolic shape enables high velocity recovery, resulting in maximizing static efficiency and reduced power cost.