Abstract: The present invention relates to a system of adjustable preformed ductwork for the conveyance of a fluid. The system uses a distribution box which includes an upper portion having a plurality of walls and a bottom plate. The distribution box may act either as a diffuser boot or as a splitter box. The distribution box is joined to interconnecting duct lines by adaptor conduits. The adaptor conduits are duct line which are adapted at one end for connection to an opening in a wall and are adapted at the other end for connection to adjoining duct line. A valve having a housing, a first cone and a second cone is also included in the system either in a duct line or in an adaptor conduit. The first and the second cone have matching apertures. The second cone is rotatable within the first cone such that the matching apertures may be selectively aligned or misaligned to adjust the flow of the fluid through the ductwork system.