IT DEPENDS ON THE SIZE OF THE GROW ROOM BUT I HAVE 3 GROW ROOMS 3X3X3 OR 10 SQ,FT I USE 2 BATHROOM FANS ONE ABOVE AND ONE BELOW TO KEEP AIR CIRCULATING . ALSO U NEED LIKE A HOLE FOR AIR TO GET OUT OF YOR GROW ROOM AND DONT LET YOUR PLANTS MOVE IT STRESSESTHEM.