The answer is an easy one, should you have enough room between the intake and the floor (and your case has a grill on the bottom for a PSU fan to draw air) you'll want to have your PSU facing downwards.
Should I mount my PSU facing up or down?
Deciding on whether to mount your PSU either facing up or down depends entirely on a few factors, namely case design, airflow with other fans, and the power supply unit itself.
Which way should a PSU be mounted?
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. TL; DR: Fan down if there's space for airflow, fan up if not.
Should a power supply fan face upside or downside?
Here is the Answer! The question of whether you should make your power supply fan face upside or downside in a case is very common these days. Most standard power supplies are equipped with a fan to blow hot air outside or take cool air inside for cooler operation.
What is a sideways PSU Mount?
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.
Should a PSU fan be facing down?
The answer is an easy one, should you have enough room between the intake and the floor (and your case has a grill on the bottom for a PSU fan to draw air) you'll want to have your PSU facing downwards. This will aid in the unit drawing in much-needed cool air when under load.
Can You mount a PSU with no vent holes?
The only time I would not mount a PSU like that is if there were no vent holes on the bottom of the case or (in the case of no vent holes) then the PSU must be raised about 1/2" from the bottom of the case to allow airflow. Yes, that is usually the intended way to mount a bottom mount PSU.