CHA_FAN On Your Motherboard – What Is It?

CHA_FAN On Your Motherboard - What Is It

What is CHA_FAN and What Does it Stand For?

CHA FAN, an acronym for CHAssis FAN, is a critical component of your motherboard. This power source is predominantly designed to support additional fans in the PC case, enhancing system cooling.

Differing from other connectors in functionality and capability, CHA_FAN headers can accommodate both 4-pin or 3-pin connectors. These headers’ ability to accurately adjust RPMs when using a 4-pin connector due to Pulse Width Modulation (PWM) is particularly notable.

With PWM control on the fourth wire of these fan headers, you gain direct authority over the speed at which your attached fans run—an upgrade not available with traditional 3-pin configurations typically running at full throttle constantly.

You can adjust fan speedmonitor temperature levels, and customize fan curves based on internal data from sensors. Utilizing this feature can improve cooling efficiencyreduce noise levels, and maintain a stable operating temperature for your PC components.

Other Kinds of PC Fan Headers:


SYS_FAN stands for system fan, and it’s designed to power and control the fans in your PC case.

Depending on your motherboard, these headers can have either 3-pin- or 4-pin connectors. With the help of these connectors, you can easily adjust the fan speed and keep your system running at an optimal temperature.

It’s worth noting that SYS_FAN headers are essentially the same as CHA_FAN headers, so don’t get confused by the terminology – they serve the same purpose! Different motherboards just name them differently!


The CPU FAN, or the processor fan, is a crucial element of your computer’s cooling system. It plays an integral role in monitoring and regulating the temperature of your computer’s central processing unit (CPU).

Designed with either 3-pin or 4-pin connectors, depending on the header type on your motherboard, these headers efficiently dissipate heat generated by intense computing processes.

Primarily designed to handle RPM adjustment based on CPU temperature data through BIOS settings or dedicated software, the CPU FAN facilitates optimal performance. The Pulse Width Modulation (PWM) technology incorporated in 4-pin headers gives you direct control over the RPM rate for precise fan speed adjustments. Thus ensuring that your system can manage demanding tasks without overheating while also reducing noise levels during less intensive operations.


This particular header serves a unique yet optional function on your motherboard. It’s primarily used for powering additional CPU fans, which boosts your system cooling when necessary.

Unlike the mandatory CPU FAN headers equipped with 4-pin connectors and PWM for precise fan speed adjustments based on fluctuating CPU temperatures, failure to connect a fan to the CPU OPT won’t halt system booting nor trigger error codes.

Many users operate their systems perfectly without ever utilizing this feature. However, those seeking enhanced performance or tackling heat-intensive tasks may find optimal use in bringing an additional processor fan into play via this handy connector provided by motherboard manufacturers.

CHA FAN vs. CPU FAN: Understanding the Differences

Features CHA_FAN Header CPU FAN Header
Function Power and control the additional fans in the PC case.  Primarily set to control the fan cooling the CPU.
Connectors Supports 3-pin or 4-pin connectors. Most often uses a 4-pin connector.
RPM Control 3-pin headers run at maximum speed, 4-pin headers offer RPM control via PWM. Typically offers RPM control, regardless of pin number.
Temperature Sensor Adjustments to RPM are based on internal temperature data such as average system or CPU temperature. Adjustments to RPM are usually based solely on CPU temperature.
Fan Curve Adjustment Can adjust fan curves and choose the source temperature sensor for individual fans.  Fan curves are typically set to respond to CPU temperature.

Should I use a CPU fan or CPU OPT?

The CPU fan header is designed specifically for the cooling fan that is directly attached to your processor.

On the other hand, the CPU OPT header is an additional optional header that can be used if you have multiple fans connected to cool your CPU. It offers similar functionality as the CPU fan header but may not provide as granular control over individual fans.

Choosing the Right Fan: Factors to Consider

Take a look at these key considerations:

  1. Size: Consider the size of your PC case and ensure that the fan you choose will fit properly. Common sizes include 120mm and 140mm, but make sure to check the specifications of your case to determine the compatible size.
  2. Airflow: Look for a fan with sufficient airflow to effectively cool your system. Higher airflow is generally better for optimal cooling performance.
  3. Noise Level: Consider the noise level of the fan, especially if you prioritize a quiet computing experience. Look for fans with low dB ratings or ones that come with noise-reduction features.
  4. Fan Speed: Determine whether you want a fan with fixed speed or variable speed control. Variable speed fans allow for more precise control over cooling performance, as they can adjust their RPM based on temperature changes.
  5. Bearing Type: Different fans utilize various bearing types, such as sleeve bearings, ball bearings, or fluid dynamic bearings (FDB). Each has its advantages in terms of lifespan and noise level, so consider which type best suits your needs.
  6. Connector Type: Check whether the fan you choose has a 3-pin or 4-pin connector to ensure compatibility with your CHA_FAN header.
  7. PWM Support: If you opt for a 4-pin fan connector, ensure that it supports Pulse Width Modulation (PWM). This feature allows for more precise RPM control and quieter operation when needed.
  8. Brand Reputation: Consider reputable brands known for producing high-quality fans that offer reliability and longevity.
  9. Price: Set a budget and find a balance between cost and performance that meets your requirements.

Installation and Setup 

  1. Begin by identifying the CHA_FAN header on your motherboard. It could be labeled as “SYS_FAN” and can be found near the CPU socket or along the edge of the motherboard.
  2. Take your chosen chassis cooling fan and locate its fan connector. You will need to check if it uses a 4-pin or 3-pin connector.
  3. If your fan has a 3 – pin connector, simply align it with the corresponding pins on the CHA_FAN header. The keying tab on both the fan connector and header should ensure proper alignment.
  4. For fans with 4 – pin connectors, align the connector in such a way that the fourth pin lines up with the PWM pin on the CHA_FAN header.
  5. Gently push down on the fan connector to secure it. Ensure that it is firmly connected to prevent any loose connections.
  6. Power on your computer and access either your motherboard’s BIOS or dedicated software for fan control settings.
  7. In either option, locate the fan control settings and navigate to the section specifically related to CHA_FAN headers
  8. You can adjust various settings such as RPM control, and temperature sensor selection.


Is CHA FAN the same thing as SYS_FAN?

Yes, CHA_FAN is the same as SYS_FAN. Some motherboard manufacturers label them as SYS_FAN ( in my experience, I’ve seen MSI motherboards labeled SYS_FAN)


MSI PRO X67oP labeled as SYS_FAN

Can I plug a case fan into CPU OPT?

The CPU opt connector is designed to provide precise control over the power and speed of the CPU cooler. Plugging a case fan into it may cause it to spin at the wrong speed or not spin at all.

This can lead to overheating of the CPU, decreased performance, and potential damage to other components.

What if I don’t have any other fan headers available?

If you don’t have any other fan headers available, you can use a fan splitter or hub. These devices allow you to connect multiple fans to a single fan header, effectively increasing the number of fans your motherboard can support.

I am a computer engineer holding a bachelor's degree in Computer Science, complemented by a Master's in Business Administration from University of Strathclyde, Scotland. I currently work as a Senior IT Consultant in Melbourne, Australia. With over 15 years of...