hey everyone!!! i have a pretty basic question. i just built my first pc last week. i have the z170 classified k mobo and put it in a nzxt s340 elite case. i also have the ftw 1070 hybrid mounted as the rear exhaust and the corsair h100i v2 up front as intake. the s340 came with 2 3 pin fans installed. i removed the rear for the hybrid and the top one is currently hooked up to the psu directly as an exhaust. 

my issue is when my system is at idle i have negative pressure in my case, once i run a game or do something cpu intensive i get a positive pressure as the fans on the h100i speed up.

my question is can i hook the upper exhaust 3 pin fan up to one of the mobo 4 pin headers and control its speed via the bios so i have  positive pressure at idle? which header should i put it on if i can? would it be a better idea to just leave the upper exhaust hooked up to the psu and maybe increase the fan speed of the two intake fans through corsair link software? 

the system is quiet and id rather have positive pressure over quietness. the temps are 20con the psu and 24c on the gpu at idle and i dont think slowing the upper exhaust a little would affect my temps much but i guess i won know until i try. : ) 

could use some advice on which solution would be best, hooking the 3 pin upper exhaust to a mobo header to lower its speed and which header to use, or increase the speed on the two intake fans associated with the h100i. 
 
thanks for the advice and help!!!

gbaker3
Hi there,
 
I am assuming you have your h100 fans connected to the CPU1 and 2 headers on the mobo? You can certainly attach the 3-pin exhaust fans to any of the 4-pin mobo headers. Just make sure that you change the operation mode in the BIOS to match the type of fan. Any headers with a 4-pin (PWM) fan should have the setting as PWM, any headers with a 3-pin fan should have the setting as Voltage Control (I can't think of the exact terminology used in the BIOS setting, but it is whichever option is not PWM).
 
I think the mobo defaults to Voltage Control, since when I connected a PWM fan to the CPU1 header it did not autodetect and I had to switch it manually. I personally wouldn't worry too much about positive or negative pressure in your case, since the thing is full of holes and will make up for the pressure somewhere.
 
*Edit*
I see now after looking it up that the h100 uses 1 CPU header to control the pump/fans. If that is the case, I'm guessing your best bet would be to attach the extra exhaust fan to the CPU2 header, that way it will increase/decrease speed at the same rate as your h100 fans.

thanks for the reply!  yes the h100i is hooked into the cpu1 fan header and the fans hook into a lead that comes from the pump. im not concerned about temps per say, it running cool just i think positive pressure is preferable because it helps keep dust out of the system by having that excess air blowing out the various holes, nook n crannies instead of sucking air in through those unfiltered areas. 

so up top on the mobo is a fan header labeled PWR_FAN, just so i understand correctly i can hook the 3 pin fan up to that and regulate its rpm in DC mode through the bios?