Hello, Well I have a 64x20x36 grow tent with a 600w hps/mh. I having temps in the 80F & 90F range. The normal room temp during the day is around 90F and 87F at night without a/c. I am thinking on buying a 400w to replace the 600w but before I do that I would like some info. I know 600w is overkill in this space but, replacing it with a 400w would make a significant change in temp considering normal room temp? What you guys think? Check out my journal for more info. Thanks!