This video shows the build of a Homemade Garage fan made out of Old Furnace blowers that is easy to make and really efficient.Once you try one of these you’ll never use a box fan again. These fans are designed to run with constant restriction. So you need to recreate this when used out in the open by blocking roughly 25% of the air intake or output. If you don’t restrict the airflow the motor will pull significantly higher amps than it is rated for and will overheat/burn out.
If you want to be scientific you can look at the side of the motor and read the rated amps. Then with a load meter hooked up, run it and block off the air flow until the amp draw drops to or close to the rated amps.Centrifugal fans are amazing at moving a large quantity of air and the output can be ducted unlike axial.