First off my grow space is 5ftW x 2ftD x 8ftH. The light being use now is a sunblaze T5-44 4 bulbs 20,000 lum. As for ventilation a 4" valueline fan and phat carbon filter attach. Day temps 75 and nights around 70. Out side of grow closet is 70 degrees. 40 % humidity. I will be flowering soon and I would like to switch to a 400 watt hps cool tube but I'm not shore how much more heat it will produce.