I use a grow tent to start a lot of my vegetable seeds, it's 2x4x6 +/- so right around 48 ft3 (48 cubic feet). Ideally I need to replace the 48 ft3 of air in my tent 1 to 3 times a minute with fresh air in order to have good air quality within the tent BUT I don't want to just pull the air in from the room that the tent is in, that air may be fine in a large area like a kitchen, dining room or garage but when that air is confined in a smaller area like my tent and everything is then magnified a great deal so the air within the tent can be stale or contaminated and in turn I'll have poor germination and/or poor plant quality and growth. I am a firm believer that in order to have good quality plants that are healthy in a tent you need, proper; temperature, humidity, lighting, soil moisture, air circulation and air filtration.
Like I said I have a tent that is 48 ft3, I run a 195 cfm (cubic feet per minute) fan with a carbon filer on my tent so it replaces the inside tent air around 3.5 times a minute and I have a good quality air filter on the exhaust vent so that the air leaving the tent is to a point filtered also. Along with this I run two 6 inch fans inside my tent circulating the air with in tent. My air quality in the ten is good to excellent and I can see a difference in the plants.