co2 vs fresh air intake

I grow in a large grow room, I run 12 - 8gallon buckets in an RDWC system, running 4k in HID. Would C02 be an option, or just a waste in a room roughly 20x20. I can just pipe in fresh air like I always do, but was wondering, if I cut the intake of fresh air and crank C02, would it be a step up...