A Simple Calculation of Fan Efficiency

When comparing ventilation fans/blowers, please consider efficiency, not just power. Divide the published CFM value by the horsepower of the motor. This tells you how much AIR you get out of all those “horses” you are going to buy, store, lift, and listen to.

Of the various VENTRY Fan models, our electric 1.5 hp fan is our most efficient. 12,000 CFM divided by 1.5 horsepower = 8,000 CFM-per-horse. That is a lot of air for a little motor. Of our gas models, the 24 inch GX120 is the most efficient (longest propeller and smallest motor), pushing 5,700 CFM per horse (20,000 CFM divided by 3.8 hp). Click here for specs, and the calculation is done in the table for you.

We figured out CFM-per-horse on multiple brands several years ago and have not had the time to do it since, but the relative data is still interesting. Click here to see the 2005 calculations.

Note, the longer a propeller is, the more efficient it should be, but this also makes the fan bigger obviously. Very few customers have the storage space or extra manpower necessary for fans that are larger than our biggest, a 24-inch prop and Honda GX200 (5.5 hp) motor. At that point, if you need even more CFM, we recommend multiple smaller fans.