it depends on your temps and how much air you need to move how big is your room what are the temps?
With only two lights id go with 6", cheaper, and the airflow doesn't need to be that great. If you pull through 4 or more id step up to 8". Remember to pull air don't push it. GL
a 6' hood will give you a more focused light for a smaller aria dipends on the number of plants and sq fottage you have to grow
i think i saw a hood vent exhaust calculator online someware at one point
i think i saw a hood vent exhaust calculator online someware at one point