I grow in a very small space with a 600W HPS. If you can keep the air outside the space cool, having a carbon filter and exhaust fan combination ducted through your lamp and the resulting hot air ducted out of the grow space will provide a number of benefits. For one, it will remove all smell from outside your grow space when the door is closed.
Also, it will create a negative pressure in the grow space, which makes plants happy. Finally, it will pull cool air from the room outside the grow space in to where the plants are, provided you placed the intake/filter inside the space.
take a look at my box in the thumbnails below. The white "can" is a carbon can filter. The metal box on top of it is a Vortex inline exhaust fan. I used insulated ducting(the kind with fiberglass inside, for hot air) because it's a LOT quieter when moving all that air around, regular ducting is LOUD!!!!.