none .........this would be a passive system
if u wanted to make a powered intake i would tell u how to build a filter box attach a anouther 6 inch booster then u can run 6 inch ducting into the grow area and use the moving fan set the ducting so it blows right under it up into the path of the fan or right behide it feeding the fan
if u wanted a power intake (do not cut the 12x12 in the door ) u would need a 6 inch round hole to allow ducting in the rest is like this
1 u get a flatrate mailing box one of the 12x12x7 ones (post office they are free large flat rate box )
2 u make the box and cut off the top 4 flaps
3 u spray the box inside with rubber to seal it (flexie seal anything that is spray rubber)
4 u take the 6 inch fan and place it in the middle of the rubberized box and press down to make a circle in cardbord
5 cut out the circle
6 reseal any areas that were damaged
7 in the hole u have made push the 6 inch booster fan tho the back so it is sucking (go passed the ridge on the metal makes a better seal)
8 duct tape the fan to the outside of the box
9 attach the 6 inch ducting to the other side of the ran
10 put it tho the door and seal that
11 get a 12x12x1 filter grade 9 or 10 and place it in the front (duct tape the edges 1/2 on the box other half on the filter this will hold it place and seal up the box so the air passes tho the filter
12 every 90 days replace the filter (or go by the light u see coming from the tent tho the filter when dust and all covers that and hard to see the light time for a new filter even if it before the 90 days) they will run yah between 20 to 16 bucks so it is 80 to 100 bucks a year for clean air for the plants ..........i use it on mine(tent system) since i am a smoker and smoke is bad for the plants
if u are talking about the moving fan inside
http://www.amazon.com/gp/product/B004I2MNBA/ref=oh_details_o04_s00_i01?ie=UTF8&psc=1
it is white
it moves 180 degrees
it clips on .................my method was to get a strip of pine trimming (98 cents) cut it to 5 feet then i duct taped it to a old paintcan (for a counter weight) and i can move the fan up or down so it matched the canopy
only down side to this fan it has a curly cord so might need a extention cord