In a couple of weeks I'm planning to start growing in a 4' x 8' tent with 2 600W MH during the vegetative stage and 2 600W HPS during flowering stage. What type of ventilation system would be ideal for my tent and how much heat will be produced by these lights ? I am not too worried about the smell (unless I should be?) so I wasn't planning on getting a carbon air filter but I will definitely be getting additional fans.
Two 6" inline fans. One for the hood loop, and one for the carbon filter (you WILL need it). An oscillating fan to keep the stalks strong and to keep the air moving.
Even if you live in a legal state you'll want a carbon filter. Nobody needs to know your business, just asks for trouble
I would go with a 1,000 hps for the whole grow. But hey thats just me. Everyone has their different ways. you want to have the carbon filter in the inside of the grow tent. if you cant fit it then outside of the grow tent will work.
A 1000w has a wider footprint than can be utilized in a 4x4 area (or being hung in the center of a 4x8). Two 600w in a 4x8 is the way to go for sure. The 1000s just put off more heat than you would want to deal with. During the summer months just keeping the 600s cool can be a chore.
You would get less yield. A 1000w bulb is not going to cover the 8 foot area. They max out at about 5foot. The original idea of 2x 600w is way better. Although 2x 1000w would be even better if you can handle the power usage and heat output
If you can run air cooled hoods like MP mentioned then 2x 6" fans would be just the job. If you are using open hoods then I would go with either an 8" or 10' fan, and maybe add a small intake fan to help it out if it needs it, but it probably won't