Types 1221-DOW and 1221-OW are "from wall" large efficiency blend hearth/smoke damper especially suitable for programs where the damper can't be installed in the plane with the wall or ground. They functions Nailor’s unique inter-locking double skin airfoil blade design that gets rid of combustible seals and presents flame and smoke seal below https://holdenjzodr.blogcudinti.com/37171091/new-step-by-step-map-for-heavy-duty-stainless-steel-damper-manufacturers