When installing your PSU, you can position it with the fan side facing up or down. In some specific cases, it can even be mounted sideways (more on that later). So, which way should you mount the PSU? That depends on the case, and sometimes the power supply itself.
Most standard mid-tower to full-tower PC cases have the PSU mounted at the back, on the bottom of the case. In most cases, there will be an opening at the bottom. If your case has this opening, mount the PSU with the fan side facing down.
This setup allows the PSU to intake fresh air directly from outside the case. Since PSUs exhaust air out the back the switch, this creates a closed system. The air is drawn in from the outside, cools the PSU, and is then exhausted – completely separate from the airflow for the other components inside your PC.
PSU area. Note the gaps on the bottom of the case to provide airflow (e.g. CORSAIR 5000D).
Most cases have a fan filter to reduce the ingress of dust and floor-dwelling nasties.
If your case doesn't have an opening beneath the PSU, you'll need to mount it with the fan side facing up. Yes, it will draw in warm air from inside the case, but warm air is better than no air. Don’t worry, PSUs don’t usually get that hot, so it’s going to be fine.
Small form factor cases typically offer only one way to mount the PSU and usually require a smaller SFX unit. Be sure to check, as regular ATX PSUs may be completely incompatible.
Sideways PSU mounts are often found in dual-chamber style cases such as the 2500 and 6500 Series. The PSUs are mounted sideways to prevent the case from being excessively wide. If your case has the PSU mounted sideways, always mount the PSU with the fan facing outwards against the side panel, not toward the motherboard tray.
This configuration used to be ubiquitous but is rare these days. Regardless, the same rules apply. If there’s a grill or other cutouts for airflow that lead outside, the fan should be positioned against this side. If not, the fan side should face the inside of the case.
Our SHIFT PSUs operate the same way as any other power supply regarding cooling, but the cable connections are on the side instead of the end opposite the power switch. If you’re using a SHIFT PSU, make sure the ports for the cables are facing toward the cable management area of the case.
In almost all cases, this will result in the fan facing down. If your case is unique, it might result in the fan facing up. As long as there is a decent ventilation around it, you’ll be fine.
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