It is generally not recommended to connect case fans to the CPU_FAN or AIO_PUMP header on your motherboard so that these can be reserved for your CPU cooler fans and liquid cooler pump (if used) respectively, however these headers are electrically identical to SYS_FAN headers. The core differences for these headers are:
- Failure Detection - CPU_FAN in particular will alert the system if a fan failure is detected (i.e. 0 RPM). This can be crucial in the event that the system may overheat.
- Higher Power Limit - AIO_PUMP/CPU_OPT headers may support a higher Power Limit (i.e. 24W or 36W) to meet the power demands of a cooling pump.
- Fixed Default Speed - AIO_PUMP/CPU_OPT headers may be set to run at 100% power by default. Connecting a system fan to this header may result in loud fan noise out of the box. This can be fixed by adjusting the speed for the header in the motherboard UEFI/BIOS.
If you are out of SYS_FAN headers however and have an open CPU_FAN or AIO_PUMP header, they can be used to connect case fans.