Purchasing from the Active Air product line means the freshest air and easiest-running systems for your indoor grow space. Getting a value-priced combo pack saves you time on purchasing as well as money, offering up some of our best and most popular products in a single not-to-be-missed bundle. The AC20 combo pack offers everything you need to set up your growing space, including: Carbon filter (AC20D16) 8" in-line duct fan (ACDF8) 8" wide mount flange (AC8FW) Pre-filter (ACPF20D16) 8" x 25' premium ducting (ACDC825M)