intake cfm's?

[moaky]

what is a recomended cfm's for the intake. i know it depends on the size of the room. but is there a calculation. i found a calculation for out take. i know it should clear the room in atleast 5 mins but is recomended at one minute. but i cant find anything out about an intake fans and what they should produce. i guess the more the better right. the main thing an intake is doing is giving new co2 right? and it wants to be a weaker fan than the outake right?

 

[FreakNature]

Your intake fan should have about 90% of the capacity of your exhaust fan. If you just had a "hole" or opening for intake you want no more than 1500 feet per minute of flow...so for a 250 CFM exhaust fan you'd want about 225 CFM inlet, either in the form of a fan or an opening of 22 square inches:

22 sq in/144X1500 FPM=229 CFM

If your supply or inlet was a cold air duct, they usually run about 1000 FPM, so you need about a 6" inlet duct for a 250 CFM exhaust:

3x3x3.1417X1000/144=196 CFM or 78% of the exhaust...a little lean but it just means the exhaust fan would work a little harder or air would be sucked in through cracks. Not too bad a situation.

I hope that makes sense...kinda late for me.