I'm going to start growing in my small closet. Do I need a ventilation system? Some guides I've seen say that leaving the door open is enough. It's a small closet, maybe 4x3.
Ventilation system? Yes, in some way shape or form you need fresh air to be available to your girls. You probably don't need to invest in a big system, but the size air system you require also hinges upon the size lighting you are using. My current set up I have a fan ducting out heat from my light, and it is a strong enough pull of air that the negative air pressure pulls fresh cool air down from the Attic. What may work in my set up may not work in yours, but I think I answered your question.
Hey man, I have the same dimensions for my closet grow. Got 2 plants in there with a 4-foot t5 fixture and a bunch of CFLs. During veg I would close the closet door while I slept (7 hours a day) and the rest of the time I'd just leave the door open and have a small desk fan on the floor running constantly. Now I'm in flowering and leave the door open during their 12 hour light cycle and have the fan running those 12 hours as well. haha so my short answer is that a small desk fan should be good enough as well as keeping the door open atleast half the day
i still need a fan this size for my grow room. went to 4 different stores today and it looks like fans are a seasonal item and sold out
They have small computer fans at radio shack. Like $18, you have to get a cord to wire it to (simple two wire setup) for $2 they have there also.