Plenums Plus is a Southern California manufacturer that specializes in fabricating rectangular, round, and flat oval duct & f ... ittings in a variety of materials. Since 1986 we have been partnering with HVAC and Mechanical contractors to provide their clients with quality duct systems at a fair price. Located in San Diego County, we have supplied projects from Central California, to Guam, Arizona, Nevada, and as far south as La Paz, Mexico. Plenums Plus fabricates a variety of other products such as; angle iron rings, electrical boxes, hoods, concrete forms, wall & floor sleeves, custom boxes and cabinets, cat walks, and a host of other items. We have capacities up to 1/4" in sheet, and up to 1/2" in angles, shapes, and bars. read more