The fan is rated 216 Cfm at 0 Static Pressure.. which means no restrictions. Depending on the style of the.. as the Static Pressure increases the CFM decreases. Static Pressure is a way of measuring the restrictions (air friction)
of a duct system.
There should be more info on the fan or in the documentation that came with the fan. What style blade does it have?
Some fans aren't designed to handle much Static Pressure and they flat line. Corrugated pipe and sharp bends are air flow killers.. 6' of corrugated pipe is the equivalent of about 75' of pipe.. regular elbows are the same as 20' of pipe
216 CFM at .02 SP needs 11" pipe or 15/6 ductwork to maintain Cfm
Any other info on the fan would be helpful