carbon filter...?

if im running a carbon filter through an inline fan, does it have to be vented to the outside to have the same odour eliminating ability?

The carbon filter is to eliminate odors for the air that will come out of the grow area. The garden area always stinks. Ya cannot get the odor out of there but ya can clean the air with the carbon filter before it exits the room.

The air passing through has the odor eliminated.. So technically, yes, you can improve the smell in a room with a recirculating system. However whatever is smelling in your room will probably give off the smell just as fast as you can clean it.

Try using an Odor Neutralizing agent bucket method if you must recirculate.