As a helper and novice -
Is there a basic CFM chart for the various flex duct sizes somewhere on the web. I have received different numbers.
from different techs. 5 inches to 14 inches
Look under performance data on left side
Basic Manual D ,from http://www.acca.org ,is that it depends on the total equivalent feet of duct in each system, to know what each size duct will move in cfms.