Calculating cfm for box w/ filter

[pot2010]

I plan on getting this filter for my box-
High Tech Garden Supply

I need to make sure I get a fan with the proper cfm. The site says in order to figure it out you need to multiply the length x width x height and then divide by 5 because he site says air should exchange every 5 min. Is this correct, should air be exchanged every 5 min? My box will run about 1ft x 3ft x 6ft. -So by the sites calculations I should need a 3.6 cfm fan, that doesn't seem right. Am I missing something, could someone please clarify?

 

[pot2010]

Anyone?

 

[CannaRebel]

I saw the item you were getting and it seems that HTG recommend getting another fan they have on their site for this filter, why not go with that?

 

[Hogdady]

The ventilation guideline is to exchange the entire volume of air in your space 3-5 times a minute. You have 18 cubic feet in your space, so you will want to move 60-100 cfm.