Knowing the difference between CPU_FAN and CPU_OPT fan headers on your motherboard is a small but crucial bit of knowledge that you will need when building your own PC. Below we explain the function of both CPU OPT and CPU FAN headers and which one is best for what, as well as giving you some additional information on alternative headers on your motherboard.
What Is A Fan Header?
Headers on a motherboard are rows of pins that form the ‘male’ (i.e. sticky out) half of a power connection, onto which cables with the female ‘socket’ counterpart can attach.
What is CPU FAN (CPU_FAN) Header?
The CPU_FAN header (as it should be clearly labeled) is the primary header on a motherboard.
As the name suggests, the CPU FAN header is the one that you need to plug your CPU cooler into (whether it be a fan or some other form of heatsink). It is vital that you do this otherwise, best-case scenario, the BIOS will not let your computer boot, worst-case scenario, your CPU could overheat and go kaput.
The main distinguishing feature between this header and the others you can use for cooling is that if there is not a fan plugged into it your computer usually will not boot, so as to protect your CPU. Similarly, if your computer is already running and the connection is disrupted (either due to a malfunction with the cooler or some other reason) then your system should automatically shut itself down.
Almost all CPU FAN headers are 4-pin, meaning that the speed of the fan be controlled by the BIOS, Operating System, or desktop software suited to this purpose when the CPU’s thermal sensors detect its temperature is increasing.
What is CPU OPT (CPU_OPT) Header?
The CPU_OPT header (short for CPU Optional) is a secondary power header which can provide an additional source of power for especially large CPU heatsinks, or alternatively (despite the CPU part of the name) can sometimes be used to power AIO/liquid cooling systems, which are not your primary CPU cooler.
The crucial difference between a CPU OPT header and a CPU FAN is that CPU OPT headers do not prevent your PC from booting or automatically shut it down if they do not detect a functioning CPU cooler; they therefore lack an important safeguard compared to CPU FAN headers when it comes to CPU cooling. It can however still give you a warning if it does detect an issue with the component.
Again most CPU OPT headers are 4-pin, so can control voltage and fan speed in response to data on the CPU temp.
What Are CHA_FAN & SYS_FAN Headers?
For everything else which is not a CPU cooling system, that does not need to be able to automatically respond to measured changes in the CPU temp: SYS FAN (short for System Fan) or CHA FAN (short for Chassis Fan) are used for power.
These can be independently tinkered with and set to different voltage levels/fan speeds depending on how you want your internal cooling system to be set up.
Final Word - How To Use The CPU_FAN & CPU_OPT Headers
As mentioned, you must always make sure that your CPU cooler (whatever it may be) has a connection to the CPU_FAN header.
Besides this though, if you have multiple fans from your CPU cooler which require multiple headers in order to power, the remaining fans/power cables can be connected to the CPU_OPT header, either just with a single connecting cable (if you only have one other fan), or via a splitter which will enable multiple fans to be powered via the CPU_OPT.
Can I Connect Pump To CPU OPT?
Yes. The CPU Opt header can be used for both fans and water cooling pumps. If you have an AIO build you will probably want to connect the pumps to either the CPU OPT, the CHA FAN, or SYS FAN headers, but make sure the radiator is connected to the CPU FAN header.
Can I Plug A Fan Hub Into CPU OPT Or CPU FAN?
Yes, you can plug fan hubs onto both the CPU FAN and CPU OPT headers, though we advise that you don’t use the CPU FAN for this in most circumstances. The CPU_FAN header should be kept just for the CPU fan/heatsink/radiator. You can use either the CPU_OPT header or the CHA FAN or SYS FAN headers to power your fan hub. Just make sure that you don’t have too many fans being powered from a single header to prevent them from overheating/overloading.
Should I set My CPU Fan To Full Speed?
Generally speaking, running your fans at higher speed is better for the other components of your computer (in terms of both performance and longevity) but will reduce the lifespan of your fan, and also create more noise, so you need to work out if this tradeoff is worth it. If your CPU_FAN header and the connector to your fan are both 4-pin, then your CPU Fan should be able to automatically ramp up as your CPU gets hotter, depending on how this is set up in the BIOS. Still, if you are overclocking your CPU then setting the fan speed to the max at all times may be a good idea if you don’t mind the noise.
Which Is Better PWM Or DC Fans?
PWM fans are better than DC in almost every respect. PWM (Pulse Width Modulation) fans tend to be capable of running quieter, are more energy-efficient and allow greater control of fan speed that DC (Direct Current) fans.
Where Do You Plug PWM Fans?
PWM fans should be plugged into 4-pin headers where possible. You can plug them into 3-pin headers, but you will lose out on the additional functionality they bring over DC fans if you do this.
Can You Plug A 4-Pin Fan Into A 3-Pin?
As above, you can usually plug 4-pin fans (such as PWM fans) into 3-pin headers, but you will lose out on the functionality of greater fan speed control etc. that they have over fans specifically designed for 3-pin sockets (e.g. DC fans).