The idea seems simple - if more air is desired to move through a unit, stack another fan on top of the first one to increase airflow - but is this how it really works? This article will answer a common question we receive: does stacking fans double the CFM (cubic feet/minute)?
In short, stacking 2 (or more) fans will not double the airflow. Here are a few principles that explain why:
The same amount of air is going from the first fan to all subsequent fans, and the air is traveling off the first fan’s blades at approximately a 45-degree angle, which increases turbulence on the intake side of any extra fans.
Stacking fans increases the static pressure, which may cause difficulties in more closed systems like a computer case. Creating high pressure will make it more difficult for fans to fight this pressure to get air across the fins - this can be minimized by removing panels/increasing openings in the case.
To counter some turbulence of stacking fans, you would have to pair a clockwise rotating fan with a counterclockwise rotating fan (such as the counterclockwise-rotating EBM Papst 700F series) - note the performance yields from this are varied and typically aren’t any more than about 20-30%.
Stacking fans directly on top of each other generally increases turbulence, static pressure, and cost without having a definite positive impact on CFM and cooling.
Ideas to increase CFM would include:
- Purchase a fan that has more CFM
- Put two fans side by side, they should move roughly twice the amount of air that a single fan is rated at.
Here’s a video that shows some of the principles discussed above:
If you have any comments or questions about this article, feel free to post your responses below.