For an 8x12' shed an 18000 btu ac is overkill. From experience you could go with a 12000. 2 gavita 600/750s and a couple t5s for veg. Or if you want to get spendy the Cob Leds are where its at. More light, less heat, more flowers... Also, as long as your window A/C is sealed, as in the little...