i just started with a fan a few days ago but i feel that it takes me temp way down too low when my lights go off. im on an 18/6 light .but it sure as hell helped my plants become stronger. a lot depends on where ur growing, my buddys oscillating fan burned out and all he was using was a 6" clip on fan. it didnt move the air enuff in his grow tent and he blames this for leaf mould.