Passive intake just means that there is no fan blowing air into your grow area, just an exhaust fan blowing air out/SUCKING air in, as opposed to an active intake where you have a fan both on the intake vent and exhaust vent. This should be plenty of suction to draw air through your intake without putting a fan there. The exhaust fan should be toward the top of the grow area and the intake hole/fan should be near the bottom because cold air is more dense than hot air.