You only really "need" to vent if you have HEAT issues, you do however need a fan in there, you NEED a charcoal filter for the smell, and my first grow was w/ a 400 and if you have already purchased.. get more light. If you haven't get a bigger light. It's as simple as more light = more bud. I've been wanting to grow again, and after all that I learned i sold all my old stuff b/c it's not the quality I want. I got 3.5oz out of 2 plants. had a 400W HPS, and a 4ft T5
Sorry I got off track, and to answer another Q, NO, venting is also for fresh air, unless you have CO2, which it sounds you like u probably don't. They will grow w/o it, but they will GROW the way you want with fresh air. honestly w/o fresh air dont waste your time in the closet, build a box you can vent!!! it's all about the end product, and if you r only growing for you, the 400w will be enough for a small box, and once you get the hang of it you will be all about trying diff strains, and the box would be ideal for it.
Sorry I got off track, and to answer another Q, NO, venting is also for fresh air, unless you have CO2, which it sounds you like u probably don't. They will grow w/o it, but they will GROW the way you want with fresh air. honestly w/o fresh air dont waste your time in the closet, build a box you can vent!!! it's all about the end product, and if you r only growing for you, the 400w will be enough for a small box, and once you get the hang of it you will be all about trying diff strains, and the box would be ideal for it.