When a CPU operates, it generates heat. This heat, if not managed properly, can lead to thermal throttling. The job of cooling systems (usually a combination of heatsink and fan) is to keep the CPU cool so that it can run at its maximum potential without interruption. Speaking of fans, all consumer grade motherboards have headers with labels CPU_FAN, CPU_OPT, etc. that allow us to connect fans. If you are building a PC and are confused between CPU_FAN and CPU_OPT, then this guide will help you understand the difference.
Here, we will look at the purpose of each header, how CPU_FAN and CPU_OPT are useful with different types of CPU coolers, and many more. Let us begin the CPU_FAN vs CPU_OPT guide.
What is CPU_FAN?
CPU_FAN is the main or primary header on the motherboard for connecting the CPU cooler fan. It is typically located near the CPU socket on the motherboard and manufacturers label this header clearly on the motherboard for easy identification.
If you are building a new PC, then you have to connect the CPU cooler fan to the CPU_FAN header. Most motherboards have a failsafe system where if you don’t plug the CPU fan into the CPU_FAN header, the BIOS will not let the system boot (unless you make some changes in the BIOS, which we do not recommend).
Apart from BIOS, most hardware monitoring and control software (such as SpeedFan, NZXT CAM, HWMonitor, etc.) use CPU_FAN header to regulate/monitor the CPU temperature.
The CPU_FAN header can have a 3-pin or 4-pin configuration. A 3-pin header provides basic fan control through voltage regulation. In contrast, a 4-pin header includes an extra pin for Pulse Width Modulation (PWM). This additional pin allows more precise control of fan speed, improving cooling performance and noise management. Most modern motherboards have a 4-pin header.
What is CPU_OPT?
CPU_OPT stands for CPU Optional Fan. As the name suggests, it is an optional header/connector for additional cooling fans. If you have a large aftermarket heatsink with dual-fan CPU coolers, then we have to connect the secondary fan to the CPU_OPT header. Apart from air coolers, some AIO (all-in-one water coolers) coolers can use the CPU_OPT to connect the second fan (the first fan goes to the CPU_FAN in case of AIO).
If your motherboard doesn’t have a dedicated AIO pump header (W_PUMP or AIO_PUMP), then you can connect the AIO pump connector to the CPU_OPT header.
Depending on the motherboard, the control of the CPU_OPT can be different from the CPU_FAN or shared. If it is a shared control, then it is very useful for dual-fan coolers or AIOs as it allows you to control both the fans with a single setting.
Similar to the CPU_FAN header, CPU_OPT can have a 3-pin or 4-pin configuration (3-pin with DC speed control while 4-pin with PWM speed control). Unlike CPU_FAN header, the BIOS doesn’t monitor the CPU_OPT header if a fan is connected or not.
What are the Differences Between CPU_FAN and CPU_OPT?
Primary vs Secondary Cooling Role
The CPU_FAN header acts as the primary connector for the main CPU cooling fan. In contrast, the CPU_OPT header serves as an auxiliary cooling connector. It supports additional cooling components like secondary fans or pumps.
Monitoring and Control
The BIOS/UEFI interface prioritizes the CPU_FAN header for regulating the CPU temperature. Users can find detailed settings for CPU_FAN, including fan speed profiles and temperature thresholds. The system relies on CPU_FAN to maintain optimal CPU temperatures.
It varies from one motherboard to other but typically the CPU_OPT header follows the settings configured for CPU_FAN. It mirrors the fan speed profiles and temperature response curves. In the following image, you can see some essential specifications of different types of fan headers on ASUS ROG CROSSHAIR X670E EXTREME motherboard. Interesting point is both the CPU_FAN and CPU_OPT have a shared control.
Safety Mechanism
The CPU_FAN header has a couple of important failsafe mechanisms. The first one is the BIOS doesn’t boot the system if you don’t connect any fan to the CPU_FAN connector. Second, the BIOS continuously monitors the CPU_FAN. If the CPU_FAN fails, the system issues warnings and can automatically shut down.
CPU_OPT plays a less critical role in safety mechanisms compared to CPU_FAN. While it helps in additional cooling, it does not prevent BIOS from booting the system or trigger automatic shutdowns if it fails.
How to Use CPU_FAN and CPU_OPT?
Using both these headers is simple. The CPU_FAN should be reserved for the primary cooling unit. You should always connect the main CPU cooling fan in the CPU_FAN header. In a single-fan air cooler setup, you have to connect the fan to the CPU_FAN header. You can also use it to install the stock CPU heatsink (if one comes with your CPU), third-party heat sink or an AIO.
In a dual-fan air cooler setup, you can utilize both the CPU_FAN and CPU_OPT headers. If you need multiple coolers or fans to regulate the temperature of your device, you can connect the second cooling fan to the CPU_OPT header. If you have only one secondary fan, you can use a direct cable connection. If you have multiple secondary fans, you can use cable splitters to split and connect all the fans through the CPU_OPT header. Keep an eye on the maximum current and power the header can handle.
You can also connect the water-cooling pumps to the CPU_OPT header. In case you intend to use a fan hub, the best choice is the CPU_OPT header.
What are CHA_FAN & SYS_FAN Headers?
CHA_FAN or Chassis fan header is where you can plug in the chassis or case fans. These fans allow you to regulate the air flow in and out of the case. The CHA_FAN can be of 3-pin or 4-pin style. The 3-pin style is an older standard, while the latest 4-pin connector offers better speed and cooling (using PWM).
The SYS_FAN or System Fan header is similar to CHA_FAN. The naming is motherboard specific. For example, Gigabyte uses the name SYS_FAN while ASUS uses CHA_FAN. But they essentially serve the same purpose.
Frequently Asked Questions
Is it necessary to use the CPU_OPT header?
Answer: No, using the CPU_OPT header is not necessary for most setups. It provides additional cooling options, such as connecting extra fans (in dual-fan coolers) or liquid cooling pumps, which can enhance the overall cooling performance.
What happens if I don’t connect anything to the CPU_FAN header?
Answer: If you don’t connect anything to the CPU_FAN header, the system may not boot or will issue warnings. The BIOS/UEFI expects a fan connected to this header in order to cool the CPU. The lack of cooling fan could cause automatic shutdowns to prevent damage.
How do I know if my motherboard has a CPU_OPT header?
Answer: To know if your motherboard has a CPU_OPT header, check the motherboard manual or better look at the motherboard itself. Manufacturers label headers clearly, making identification easier. The manual will list all available headers and their locations.
Do all motherboards come with a CPU_OPT header?
Answer: No, not all motherboards come with a CPU_OPT header. Typically, high-end and enthusiast motherboards include this header to support advanced cooling setups (large air coolers with two fans). Entry-level and budget motherboards often lack this feature.
Conclusion
CPU_FAN header is for connecting the primary cooling fan of the CPU. It helps in regulating the CPU temperature. On the other hand, you can mount the secondary CPU cooling fan (or a radiator) on the CPU_OPT header.
These two headers have different purposes. Hence, you should be careful about choosing CPU_FAN vs CPU_OPT headers while connecting fans or other cooling units.
