So what happens if a grow room cools to 60-65 degrees F (or lower) during the dark hours? I think the temp with the lights on will be in the mid to upper 70's, but as it's a new grow room it has yet to be tested. I know things get arid in an unvented closet. 2012's closet grow ended in May. Temps fluctuated between 78 and 90 from dark to light hours and the plants regularly thirsted for water as they were always warm. But a grow room a in basement that's not particularly well heated and winter on it's way, that's a new experiment. I've read on these pages that the cool damp environment could cause mold or bud rot, if I'm not mistaken. But I'm very leery of using a space heater for the dark hours. Any advice?