Active Air Inline Filter, 6"x24"The Next Advancement In Carbon Air Filtration Is here! Active Air Inline Carbon Filters are installed inline for maximum versatility in filter and fan placement. The carbon filter is no longer limited to being located inside the grow room! Most carbon filters are designed to be "terminal" they are closed at one end and must be at the end of the ducting line. Active Air Inline Filters can be located wherever you want them to be because they do not pull