Calculating cfm for box w/ filter

I plan on getting this filter for my box-
http://www.htgsupply.com/viewproduct.asp?productID=49749

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?

3.6 is technically right but you are not going to be able to pull through a filter with that small of a fan. Also depends on lighting situation. You could probably get away with a couple good PC fans but I dont know how you would use a filter with that.

I'm on my first grow, so don't take my comments as gospel. I think this is one of those things everyone has had a diff answer on in my research. Some say 5 times a min, some less. Try your calc based on that. I think grow room size plays a factor as well. Huge grow rooms probably need to be exchanged less than a cabinet. While more seems to be better, at a certain point you will get diminishing marginal returns. A lot of this also has to do with heat exhaust and not just air exchange. So fan placement is key as well. I couldn't see the link for the filter...curious to know what you are getting for that box.

Well I've found a couple of nice duct fans that would connect to it, the one I was looking at was a 200 cfm. Is that going to be too powerful? I've read that if the air is pulled too fast the filters cant filter it as effectively. I plan on running about 12 cfl's.

I updated the first post with the link

The recommended cfm for that filter is 160, would that be enough for my box with 12 cfl's?

That will be adequate, although I would go for the combo. With 170 cfm and 16 cubic feet, you would be at 10 times a min. What I'm wondering for you and I is how to fit that thing in the box. May be overkill

It would only be like a 6 inch duct fan, I found some at home depot that are 170 cfm, is over kill necessarily a bad thing?

You're probably talking about a duct booster fan from home depot?
Those fans don't really have enough power to do much. Their CFM rating is for absolutely no resistance in the air stream. When you add the filter they're pretty worthless.
HTG has 4in fan and filter combos that should suit your application very well. They give a pretty good price break when you buy them together.
Good luck fitting them in your box though. While pulling air through the filter is most efficient, you can push air to the filter mounted outside the box with little loss of cooling capacity. If you mount the fan inside the box, this set up should be pretty quiet too.
Hope this helps,
Fred

Thanks for the info, I'm a noob at his which is why thought hay duct accelerator would work lol. I'll probably get that combo then from their site. That should take care of my exhaust and smell. As for passive intake, with a system like that how big/many holes should I have? Could I use like a 85cfm pc fan or should I stick too passive?

Passive intake is always best. Start with 3-4 2in holes spread around the bottom. It's easy to add more, or to plug smaller holes.
Fred

But what if the bottom of my grow box is sealed off by the rim of the box? I plan on using like a armoire cab and some have a rim all around the bottom. I planned in using an active intake for this reason unless I could still work with a passive intake even though it's sealed off.

your intake doesn't have to be at the very bottom but as low as is practical, most recommend a passive vent be 2x the size of the duct drawing air out but I go larger and use 2-3 furnace filters to block any unwanted critters from finding a way in.