Running a bigger fan then the hood ducts is beneficial and will provide more cooling power to your lights which in turn will make them run for longer at a higher output. Remeber that friction only takes place between solid materials, when dealing with gases i.e. co2 or air there are simply positive or negative pressures, in conjunction with this it's always good to keep a positive pressure inside ur room to help keep dust, spore, small insect eggs etc outta your op. hope this helps...... Take it easy