This isn't an exhaust hood over a cooking appliance, is it? If so, you'll have to also consider keeping the velocity of the air high enough to entrain the particulates and grease. If not a kitchen application, listen to MintJulep.
Marthab
I do not know where you live, but here is a PDF of the code guidelines where I live. Most states are not that much different.
Pay attention to page 10.
Berkshire
I am surprised that NFPA 96 is not part of the listed standards governing the design and installation of kitchen exhaust systems in your neck of the wood.
Also: NFPA 96 allows lower velocities as low as 500 FPM nowadays for some specific applications such as Melink control systems.