Astria 18-inch Section Double Wall Pipe 18-8DMAstria 18 Inch Double Wall Chimney Pipe with Snap Lock Design How does the Astria 18 8DM chimney pipe improve installation and performance in wood burning chimney systems? The Astria 18 inch Double Wall Chimney Pipe (Model 18 8DM) is designed to extend your wood burning chimney system safely and efficiently. It features a double wall construction with a galvanized steel outer shell and a stainless steel inner flue pipe, ensuring durability and optimal