Free Fan Vs. Actual CFM Ratings - What's the Difference?

Unlike virtually all other dust collector manufacturers, Oneida Air Systems promotes and publishes “Actual CFM” ratings for our dust collectors.  These ratings reflect the real-world operating performance of the fan blower once the filter, cyclone, and flex hose (10ft) are attached. “Free Fan” ratings, on the other hand, are typically measured as either the fan blower's performance with nothing attached to it or, even worse, the theoretical maximum volume of air that can move through a specific pipe diameter. Every component attached to the fan blower adds air resistance that reduces the actual CFM.  Therefore, “Free Fan” CFM ratings, which can be nearly double the “Actual CFM” ratings, are impossible to replicate in a real world environment.

Shop owners deserve to know what they're buying, and only knowing the "Actual CFM" rating lets you properly allocate airflow (CFM) to each of your tools when designing your shop. If during your competitive research you encounter CFM ratings that seem too good to be true, ask the manufacturer for a fan performance curve. It will look somewhat like this:

A fan curve will show you how much CFM the dust collector will provide at any given static pressure, which can be calculated base on what ducting/hose is connected to the system. Click here to learn more about sizing your ductwork.

Airflow Performance Through Static Ductwork

Refer to this table to see the maximum volume of air that can be physically moved through a specific pipe diameter (CFM = Velocity * Cross-Sectional Area). Any manufacturer that lists these values as their CFM rating is not providing realistic data.