600w air cooled hps/mh in closet

4-6 plants under a 600W should yield you some pretty good numbers. I don't know how stealthy you want to be, but when I did it I took off the doors and stapled white and black poly to all the walls and where the door was, then i stapled on cardboard to the doors side and ran my ducting in through there, the cardboard was just to give some support. If you staple poly remember to always put duct tape at the spot before you staple or they will just rip out. Also keep in mind that the fans you need will probably be loud as fuck.

Edit: If you LST the plants that will boost your yield also, but its quite annoying doing it with really bushy plants like indica's.

 

Just keep in mind that temperature in the grow space (with vented reflector) still might be 10-12f higher than intake temperature .Do a dry run , before germinating any seeds to make sure temperature is on the acceptable level .