Short answer: fan down, if your case has a vent with a dust filter under the power supply and the PC stands on a hard surface or feet. Fan up if there’s no vent, or the PC sits on carpet.
Why fan down is usually better
With the fan facing down, the power supply pulls cool air from outside the case and blows it straight out of the back. It doesn’t share warm air with the graphics card, so it runs cooler and quieter.
When fan up is better
- No vent underneath. Fan down would choke the unit.
- Carpet or a rug. It blocks the intake and pulls in fibres.
- Very low feet with little clearance below the case.
Fan up draws warm air from inside the case. That’s fine for a good unit, but the fan may spin a little faster.
Quick guide
| Your setup | Mount it |
|---|---|
| Filtered vent below, PC on a desk or hard floor | Fan down |
| No vent below | Fan up |
| PC on carpet | Fan up, or raise the case |
| Small form factor case | Follow the case manual |
Keep it clean
Fan down only works if the filter is clean. Pull it out and clear the dust every few months, more often with pets. A clogged filter makes the fan work harder and the unit run hotter.
Check the cables
When mounting fan up, make sure no cable can touch the fan grille. A cable brushing the fan causes a ticking noise. See power supply noises.
Fitting a new unit? See how to install a power supply.
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Questions
Does mounting the fan up damage the power supply?
No. It just draws warmer air, so the fan may run faster.
My case has no vent under the power supply. Which way?
Fan up.
Does it matter for a semi-passive unit?
Less so at light loads, but it still helps when the fan is spinning.
How often should I clean the power supply filter?
Every few months, or monthly if you have pets or a dusty room.
Can I mount it fan down on carpet?
I wouldn’t. Raise the case on a board or feet, or mount it fan up.
Sources
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