Do I have to use sys fan 1?

[pjmadguy]

Do I have to use sys fan 1 or can i just use 2 & 3?

 

[Mr Kagouris]

You can use any combination of the onboard fan headers. They all function separately.

 

[Barty1884]

The only fan header you 'must' use, is CPU_Fan, otherwise CPU cooling isn't controlled & then you're likely to either not POST, or overheat.

As Mr K stated, you can use any combination of fan headers, they don't have to be in ascending order.