How big is your grow? How many Lights? What is size of your extractor? You can have a passive intake to allow air to be sucked in by the negative pressure the extract fan creates. A passive intake could be a hole connecting to another room or even the window, leave it open a few inches, cover window with blinds then black mesh behind blinds. then make a wooden window cover or simply glue plywood over it. Cover whole thing with black/white foil to further block light escape, cut a hole in plywood cover with mesh to stop bugs entering. I made a little hatch in mine so I could still open and close window