Often the most difficult step when building or upgrading a gaming PC is connecting all the power cables.
It can be disheartening to install one of the best gaming CPUs and a third-party CPU cooler only to find that there are two places to plug in its fan and you have no idea which header to use.
A CPU fanโs connector can be plugged into either the CPU_FAN or CPU_OPT header on your motherboard—but choose wisely, because having it plugged into the wrong one can lead to your system not booting and your BIOS throwing out errors.
The long story short is that you must have a CPU fan plugged into the CPU_FAN header, otherwise your motherboard likely wonโt register that thereโs a CPU fan connected at all.
Itโs usually only when you need to connect multiple CPU fans that you should consider using the CPU_OPT header.
What is CPU_FAN?
A motherboardโs 4-pin CPU_FAN header is its primary header for plugging in your CPU coolerโs fan, and itโs usually located near the CPU socket. Your motherboard should register this CPU_FAN header as the primary one for CPU cooling. This means if thereโs no fan connected to the CPU_FAN header, your motherboard will likely think thereโs no fan cooling your CPU at all and will prevent you from booting the system.
Because of this, itโs crucial that you have your CPUโs fan plugged into the CPU_FAN header. This lets your motherboard see that the CPU is being cooled, and it lets you configure and regulate the CPUโs temperature by adjusting CPU fan speed in the BIOS.
What is CPU_OPT?
A motherboardโs 4-pin CPU_OPT (โCPU Optionalโ) header is its optional header for plugging in CPU fans. If your CPU cooler uses two different headers, you can plug the main one into your CPU_FAN header and the other one into your CPU_OPT header. If there are more than two headers, you can use a splitter to combine them and plug the secondary ones into the CPU_OPT header with one cable.
Your system should boot without anything plugged into CPU_OPT, and its primary use is for connecting cooling systems with multiple fans, or for powering AIO cooling pumps when you canโt use the AIO_PUMP header on the motherboard. Just be aware that you wonโt be able to control the AIO pumpโs speed in the BIOS if itโs plugged into CPU_OPT.
CPU Fan Header Locations
Both CPU_FAN and CPU_OPT headers should be located close to your motherboardโs CPU socket.ย Theyโre often found side-by-side, up and to the right of the CPU, somewhere near the DIMM slots for RAM. Your motherboard should have โCPU_FANโ and โCPU_OPTโ written right next to these headers.
Their locations can vary depending on the motherboard, however. If you canโt find the headers you should check your motherboardโs manual which should have them clearly labelled on a diagram.
Can You Use CPU_OPT for Case Fans?
You can use the CPU_OPT header for case fans, but itโs not recommended when there are SYS_FAN (โsystem fanโ) or CHA_FAN (โchassis fanโ) headers available. Just like CPU_FAN, CPU_OPT is linked only to the CPUโs temperature sensor, meaning itโs not linked to overall system and other component temperatures. As such, if you plug a case fan into the CPU_OPT header, you wonโt be able to regulate its speed based on the overall system temperature—instead, it will only be regulated by the CPUโs temperature.
However, if you have no more SYS_FAN or CHA_FAN headers free on your motherboard and you need to plug in another case fan, you can plug it into CPU_OPT.
CPU_OPT vs CPU_FAN
Both CPU_OPT and CPU_FAN headers can be used for CPU fans, but, as the names suggest, only one of these is โoptionalโ. There must be a fan plugged into the CPU_FAN header, otherwise your motherboard will likely think thereโs no fan cooling the CPU and it wonโt let you boot.
CPU_OPT should be used for secondary CPU cooling connectors, such as you might find in a multi-fan radiator setup. It can also be used for an AIOโs pump if you canโt connect it to the correct AIO_PUMP header, but this will mean you canโt control the pump speed from the BIOS. Finally, you can plug case fans into CPU_OPT if there are no SYS_FAN or CHA_FAN headers available, but these fansโ speeds will then only be regulated based on the CPUโs temperature, and not the systemโs overall temperature.