Need advice on ventilation

Im in the process of building a small grow box in my closet. My original plan was to have only one fan running on the exhaust and just a hole for intake about 1/2 " larger then the exhaust fan which is an 80mm fan "3inch fan". My box is 5ft tall, 18in wide and 20in deep. It is only going to grow one plant at a time. As long as i have done my math correctly it is about 14.4ft area for circulating. (using wxdxh in ft). the fan is rated at 34.5 cfm's. Now should i add a fan on the intake side or should exhaust fan alone have enough circulation. im mouting the exhaust up top and the intake hole will be about 6in from the bottom. I just want to make sure there will be enough air transfer. Thanks for any help.

If you were to add another fan i would add a second exhaust and possibly make the passive intake a bit larger. Depending on the wattage of light used you may be ok the way it is. Will the space that the intake pulls from be cooled?

or just make sure your intake fan is less than 34.5 cfm....

and yes i would def add an intake fan.

Yeah it will be a few degress cooler