Set cooling fan airflow so cool supply air reaches the highest-heat components first and hot air exits without returning to the intake. Verify the airflow arrow molded on the fan frame, not the visible blade shape.

An axial fan is usually better for moving a large volume of air through a low-resistance enclosure, while a centrifugal blower is usually better when air must pass through dense heat sinks, filters, narrow ducts or other high-resistance components.

Cooling fan airflow can be estimated from the equipment’s heat load and allowable air-temperature rise.

A high temperature cooling fan should be selected by its real inlet-air temperature, required airflow at static pressure, bearing life, motor insulation, cable material and environmental exposure.