How high do I need the CFM on my inline fan to be?

So I'm planning on growing for the first time. I myself am not the greatest handyman which is why I am so pleased with the amount of wonderful resources that the members on this forum have contributed. Bodom's rubbermaid growbox looks pretty noob friendly for someone who needs an ideal yet simple stealth grow (living with my GF who is a bit of a worrier so the less she knows the better), so I've decided that that will be my first attempt at a grow. Unfortunately he doesn't seem to be active on here anymore, so that's where you guys come in.

The thing I'm not sure about is this: for a growbox of that size, what should the CFM be on a 4 inch inline fan? As I mentioned, this is going to be a stealth grow in a closet, so I recognize that a good dictum to stick to is "the more airflow the better", but I'm trying to gauge the point where it would be overkill, as I am also doing this on a budget.

For example, here is the Vortex which I have seen mentioned on these forums before: Vortex 4 inch 172 CFM High Power Inline Fan @ Businesslights.com 172 CFM, but also 100 dollars. Ugh.

Then there are more generic models such as this: Amazon.com: 4-inch 110VAC 80CFM in-line duct booster fan: Home & Garden Half the airflow but also one fourth the price.

So about what should I be aiming for to help keep my box at a desirable temperature?

Thanks ahead of time for any potential responses; these forums are by far the most informative source for a fledgling grower such as myself :thumbsup:

And for the record I'm planning on copying everything as it was done by Bodom in his thread, so that means the wattage of the bulbs and everything will be the same. Since I forgot to put this in the OP, here is the guide I'm talking about for reference if you have no clue what I'm talking about: http://boards.cannabis.com/grow-faqs...b-growbox.html

It's going to depend on the size of the space, the size of the light, and the type of filter system you are using, if any.

The closet is approximately 5 x 2.5 x 8; for the lights I was planning on just using 6 26w CFLs; and as for the filtering, I'm looking to do a DIY carbon filter. I'm also going to angle the passive intake at 90 degrees to keep light from escaping.

...and after more poking around on here I just noticed that a lot of this information is already in this post: http://boards.cannabis.com/1634834-post6.html. Blah. Well, any other input is definitely welcome. The more information the better.

Actually, here is a question I have that doesn't seem to be addressed there: is it possible for a fan to be *too* powerful for the dimensions of the area? I'm sorry if this is an incredibly stupid question, I just want to make sure.

One hint. Those duct booster fans do not work as well as they claim. Once you start to obstruct the flow with filters and such you lose a lot of cfm. Overkill would be what I have(an old furnace blower) even on the low setting it will blow the filter off if it is not screwed on.

I'm thinking I'll go with 260 to be safe. I don't want to overdo it and have a fan that you can hear all throughout the house or something