I'm having ventilation issues with the design. I'll post the question again here since there is a pic with this thread. Assuming I have an air cooled reflector at the top of this space, how do I design the venting? I have already ordered a 4" vortex fan and carbon scrubber but I am unsure how to incorporate that into the space as well as the reflector. It was suggested to me that I need a separate vortex fan and aluminum duct work for the air cooled reflector. Then I would need another duct for grow room ventilation. I'm just having a hard time understanding why I cant hook the carbon filter to one side of the reflector and then the fan to the other side of the reflector. This would suck air from within the room, through the air cooled reflector and then up and out through the attic. What's wrong with that setup? Why would the hydro salesman want a separate duct for the light? The light is a 600watt by the way, which is probably way too much for this space. Thoughts?

Facts about this pic: a hot water heater is on the left side of the space, this spot is in the garage that is exposed to the attic since there is no drywall ceiling in there and finally on the right side of the space as well as to the back is my home. How should I run the ventilation system?