Pre filter on external wall of ducting in AutoCAD, dwg file

This Architectural Drawing is AutoCAD 2d drawing of Pre filter on external wall of ducting in AutoCAD, dwg file. Pre-filters are used in conjunction with secondary filters and give your HVAC system an advantage over a system without them. The job of a pre-filter is to protect the secondary filter by capturing the larger dust particles, giving longevity to the more expensive secondary and final filters.