Power Supply Unit Orientation and Installation Location for Custom PCs

When building a custom PC, the orientation and placement of the power supply unit (PSU) are important factors that affect performance and stability.

In recent PC cases, it is common to install the power supply unit at the bottom of the case with the fan facing downward.

However, some cases allow the PSU to be installed at the top, or the fan to face inside the case. This article explains the differences between these setups.

This article also explains the basics of PSU standards, cables, and how to choose a power supply unit from the perspectives of performance and compatibility.

≫ Related article: How to Choose a Power Supply Unit for a Custom PC [Performance / Features / Compatibility]

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About PSU Orientation and Placement

First, let’s cover the basic knowledge about PSU orientation and placement.

PSU Orientation

There are two ways to orient the PSU fan: facing outward or facing inward.

The current mainstream is to have the fan facing outward.

When the Fan Faces Outward

With the fan facing outward, the PSU fan is directed toward the outside of the case and draws in air from outside.

As explained later, the PSU can be installed at the bottom or top of the case.

So, if installed at the bottom, the fan faces downward; if at the top, the fan faces upward.

Because the PSU always draws in outside air, it is less affected by the heat inside the case and can maintain stable operation.

Inside the case, there are many heat-generating parts like the CPU and GPU, but if the fan faces outward, the airflow inside the case is separated from the PSU.

Especially for gaming or creative work, which tend to generate high loads and heat, it is better to install the PSU with the fan facing outward.

Also, if the PSU is exposed to high temperatures for a long time, its lifespan may be shortened.

The main factor affecting PSU lifespan is the internal capacitor (a component that stores electricity), which is sensitive to temperature.

Therefore, facing the fan outward helps lower the internal temperature and reduces the load on the capacitor.

Capacitors lose lifespan much faster as temperature increases. Specifically, for every 10°C increase, the lifespan is halved; for every 10°C decrease, the lifespan doubles (Arrhenius law).

If the internal temperature of the PSU is not well managed, the capacitor will deteriorate quickly, affecting the stability and lifespan of the entire PSU.

On the other hand, if the custom PC is placed on the floor, it is more likely to suck in dust.

Therefore, check if the PSU fan area of the PC case has a filter.

While the filter can reduce dust entry to some extent, it will need to be cleaned relatively often.

If the PC is placed on a desk, it will suck in less dust.

This article also explains how to clean and place a custom PC.

≫ Related article: How to Clean a Custom PC and Required Tools [With Photos]

≫ Related article: How to Place and Position a PC Case

When the Fan Faces Inward

With the fan facing inward, the PSU fan is directed toward the inside of the case and draws in air from inside the case.

Even if the custom PC is placed on the floor, since it draws air from inside the case, less dust will enter.

However, since it draws in warm air from inside the case, the PSU’s cooling performance may decrease.

Especially if the CPU or GPU is under heavy load and the internal temperature rises, it may affect the PSU.

Also, if the case temperature is high, the fan speed will increase to maintain cooling performance.

This means the PSU fan may spin faster and generate more noise.

However, in that case, the CPU and GPU fans will also be loud, so their noise may be more noticeable.

PSU Placement

There are two possible locations for the PSU: at the top or at the bottom of the case.

The current mainstream is to install the PSU at the bottom of the case.

The PSU is a relatively heavy part, so installing it at the bottom of the case lowers the center of gravity, increasing the physical stability of the entire custom PC.

For everyday use, the center of gravity may not matter, but in the event of an earthquake, a lower center of gravity helps prevent wobbling and reduces the risk of the PC tipping over.

Also, there is a chance of bumping into the PC when moving or carrying things.

These situations are rare, but since a custom PC can cost 200,000 to 300,000 yen, it is important to consider the risks.

The Orientation and Placement Depend on the PC Case

To choose the orientation and placement of the PSU, a compatible PC case is required.

Not all PC cases allow free placement, so it is necessary to check the case carefully before deciding.

Product specifications often do not mention orientation or placement, so check the gallery or look for intake holes around the PSU area to determine the orientation.

Basically, the PSU orientation is determined by the PC case, but some cases support both orientations.

For ATX power supplies, the screw holes are asymmetrical, so they cannot be installed upside down.

However, some PC cases have a removable frame for the screw holes, which can be flipped to match the asymmetric holes of the PSU.

On the other hand, SFX power supplies have symmetrical screw holes, so they can be installed in either direction.

Therefore, when deciding the orientation of the PSU, it is important to check the specifications and design of the PC case being used.

Specific Examples and Features of PSU Orientation

When installing a PSU, both orientation and placement matter.

There are two orientations (fan facing outward or inward) and two placements (bottom or top of the case), making a total of four patterns.

This section explains the features of each installation method.

Fan Outward + Bottom Placement

This method installs the PSU at the bottom of the case with the fan facing downward to draw in air from outside.

This is the most common installation method, and unless another method is chosen intentionally, this is usually the default.

With this method, the PSU fan draws in fresh air from outside the case and efficiently expels internal heat, providing effective cooling.

This keeps the PSU temperature low, which can extend its lifespan, and since the case airflow does not directly affect the PSU, stable performance can be expected.

Also, since the PSU is a heavy part, installing it at the bottom lowers the center of gravity and improves the stability of the entire case.

On the other hand, if the custom PC is placed on the floor or carpet, it will collect more dust and is more likely to suck it in.

Most PC cases have filters, but if you plan to place the PC on the floor, check if a filter is included.

If placed on a desk, there is less dust, but it is still better to have a filter.

Also, placing the PC on a carpet may reduce ventilation, so be careful where you put it.

A filter minimizes dust entering the PSU, but regular filter cleaning is necessary.

All installation methods require regular cleaning, but dust will accumulate faster with this method, so cleaning should be done more often.

If the filter is not cleaned regularly, noise may increase.

Most PSUs can adjust fan speed according to temperature.

If cooling performance drops due to dust and the temperature does not decrease, the PSU will increase fan speed to improve cooling.

Fan Outward + Top Placement

This method installs the PSU at the top of the case with the fan facing outward (upward) to draw in air from outside.

There are few PC cases that allow the PSU to be installed at the top, so this is not a mainstream method.

With this method, the PSU fan draws in fresh air from outside the case and efficiently expels internal heat, providing effective cooling.

This keeps the PSU temperature low, which can extend its lifespan.

Also, since the case airflow does not directly affect the PSU, stable performance can be expected. This is the same as “Fan Outward + Bottom Placement.”

Since air is drawn in from the top, less dust accumulates compared to the bottom.

However, installing the PSU at the top can negatively affect the airflow inside the case.

Since heat rises, modern case designs typically draw air in from the front and expel it from the back and top.

Therefore, in cases with the PSU at the top, there is no space for fans to expel heat from the CPU or GPU at the top.

Usually, only one fan can be installed at the back, so exhaust may be weak, reducing cooling performance.

Also, since the PSU is heavy, placing it at the top raises the center of gravity and increases the risk of the case tipping over.

Especially with large PSUs, top placement can make the case unbalanced.

It is usually fine, but during an earthquake or when moving the PC, it may wobble or fall if bumped.

Fan Inward + Bottom Placement

This method installs the PSU at the bottom with the fan facing inward (upward) to draw in air from inside the case.

With this setup, the PSU fan draws in air from inside the case and expels heat outside.

This reduces dust intake, so cleaning is needed less often.

However, there is still dust inside the case, so it is not zero.

On the other hand, since it draws in warm air from inside the case, the PSU’s cooling performance may decrease.

Especially if the CPU or GPU is under heavy load and the internal temperature rises, it may affect the PSU.

This setup may also disrupt the overall airflow inside the case, potentially affecting CPU and GPU cooling.

Since it draws in air from inside the case, if the temperature is high, the fan speed will increase to maintain cooling performance.

This can make the PSU fan louder.

However, since the CPU and GPU are also under heavy load, their fans may be louder.

Compared to “Bottom Placement + Fan Outward,” there is a trade-off between cooling performance and dust accumulation, so it depends on which is more important.

Less dust is attractive, but the possible drop in cooling performance is a significant disadvantage.

If dust is a concern, “Fan Outward + Bottom Placement” and placing the PC on a desk can greatly reduce dust while maintaining cooling performance.

Fan Inward + Top Placement

This method installs the PSU at the top of the case with the fan facing inward (downward) to draw in air from inside the case.

Again, few PC cases allow the PSU to be installed at the top, so this is not a mainstream method.

With this setup, the PSU fan draws in air from inside the case and expels heat outside.

This reduces dust intake, so cleaning is needed less often.

However, there is still dust inside the case, so it is not zero.

On the other hand, since it draws in warm air from inside the case, the PSU’s cooling performance may decrease.

Since heat rises and airflow is from the back and top, the PSU will draw in warm air.

To compensate, the fan speed will increase, which can make the PSU louder.

Overall, this installation method has few advantages.

Summary: “Fan Outward + Bottom Placement” is Standard

This article explained the basics of PSU orientation and placement, as well as the four possible patterns.

Here are the key points again:

The current mainstream is to install the PSU at the bottom of the case with the fan facing outward.

If the PC is placed on the floor, dust will accumulate more easily, but the filter will prevent it from entering directly.

Although this is a disadvantage, it is more important to lower the center of gravity for physical stability and to maintain cooling performance and extend lifespan by cooling with outside air.

This article also explains the basics of PSU standards, cables, and how to choose a power supply unit from the perspectives of performance and compatibility.

≫ Related article: How to Choose a Power Supply Unit for a Custom PC [Performance / Features / Compatibility]

あわせて読みたい

PC Parts Estimation & Compatibility Check Tool

Automatically checks each component you need when selecting parts for a custom-built PC—perfect for beginners.