US Patent 7798533 Ventilation chimney section and method

A ventilation chimney or exhaust fan flue section for hog barns has inner and outer plastic tubes formed by edge welding plastic sheets. A snug fitting insulation sheet is slid between the tubes. Collars of male and female coupling elements are inserted into the ends of the section between the inner and outer tubes and secured by screws passing through the outer tube and into the collars. The chimney can be installed by combining sections using a suitable adhesive.