I recently built a new PC and noticed something odd with my power supply unit (PSU). It's mounted in an NZXT H6 Flow case, and I've got a Corsair RM1000x installed. While checking the back of the case, I found dust accumulating around the PSU exhaust area. When I held a tissue up to it, the tissue actually got pulled towards the PSU, making it seem like air is being sucked in, which surprised me because I have three intake fans at the front and two at the bottom. There are no exhaust fans installed anywhere. Initially, I thought it might be wrong to mount the PSU in a certain way, but it doesn't seem possible. After checking further, I noticed that the PSU does indeed blow air out at the top but pulls in air at the bottom. Can someone explain why this is happening? Am I missing something here?
3 Answers
Your PSU fan is actually designed to pull in air, which it then exhausts out of the back. This is standard operation for PSUs, so what you're seeing with the dust is normal. It pulls in fresh air from the side and dumps it out the rear, unaffected by your case's fan configuration. Consider adding some exhaust fans on the top or back of your case to help with airflow overall.
Yeah, the PSU is programmed to intake air from the side and vent it out the back. If you have the fan side of the PSU facing the mesh of your case, everything's functioning as it should. The positive pressure from having more intake fans won’t affect this isolated airflow.
You're right! The PSU works by pulling in air through its fan and releasing it out the back. With most of your fans being intake, you're creating a positive pressure situation that uses all openings to flush out air. It’s not negative pressure; that would mean too many exhaust fans pulling air out.

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