a 4 inch Can Fan would be ok for you. If smell is not an issue you don't have to have a carbon scrubber but you could still put a intake filter on your intake so your not sucking in dust, spores and any other unwanted stuff into your lights and tent. Just put a Can Fan sucking through your light and out the tent then you get rid of the heat and on your intake just have a filter.. I use a furnace filter ''HEPA'' and it works very well removing things like that. The more air movement the better off you are imo