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stacking fans

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Feb 4, 2002
Wethersfield, CT
I was thinking of bolting two 120mm Fans together and putting them in an exhaust at the top of my case. Would these fans sandwitch together produce double the airflow going through them or would the gain be small?
There have been various articles about fan stacking, and as I recall, the majority seemed to indicate that the fans often worked against each other, and/or produced a reduced airflow.
well two fans going the same way clockwise and clockwise

i saw somthing if you can find a cw fan and a ccw fan they will work good together

The only benefit of stacking comes when the fans are at opposite ends of a duct. It helps to fight static pressure and give the fans' full ariflow, instead of a reduced airflow for shoving air thru a narrow space. Also fans stacked close to eachother can hum if they are not exactly in sync. Like two instruments playing the same note, but one is out-of-tune.
Agreed, the two fans stacked aren't very effective. A single 120mm exhaust fan at the top is really enough. If you need to have mega exhaust out the top, you can always go with a high speed 120mm fan.

what would be cool would be to build a duct with 3 or 4 60mm's spread out in it, run the wiring inside, just use duct tape or packaging tape. if it needs to go a long distance, several feet. then it might be a novel idea.
Basically yah..

Stacking fans is pointless. You are restricted by the capabilities of the last fan in the chain. If you have a 80cfm on top and the bottom is a 40cfm your output will only be 40cfm or even lower as per what arkaine mentioned above. When fans are not in synch they will work against each other.