My bad, sorry. I explained it wrongly.

I'm using a wardrobe as a grow room. So the exhaust fan filters the air and gives it into the room again. And the intake also takes air from within the room.

In other words, there's no fresh air entering the room from outside unless the room's window is open...

I have sealed the closet entirely except there's no carbon stuff on the intake opening. (Is it possible that some air can flow through the intake fan to the opposite direction?)