as far as a carbon filter, i never used one.. how well do they work and how long do they last? im gonna be growing 5 plants, and its probably a pretty dusty room. is their a replaceable filter, or do you need to buy a whole new one? my rooms is 10x7x8, if i get a 490cfm vortex fan, and leave it on for 18/12 hours as needed, will it still recycle all the air in the room?