200 to 400 CFM
Inline fans rated between 200 and 400 CFM. This range covers most 4-inch and 6-inch duct runs, and tents or small rooms up to roughly 400 cubic feet exchanging their full volume about once a minute.
Size the fan to the room, not to the light. Start by dividing the room's volume in cubic feet by the number of minutes you want a full air exchange to take, then add 20 to 40 percent back for the carbon filter, the length of the duct run and every elbow in it. LED fixtures put less sensible heat into a room than the HID lamps this guidance was originally written around, so an LED room of a given size usually lands at the lower end of the range. Our guide on how to find the right CFM fan walks through the calculation.
