I currently have one exhaust fan and no intake fan, but I'll be getting an additional fan soon. The question is that should I place the fan as a intake fan or another exhaust fan? My motherboard only supports two fans.
The most important fan is the exhaust next to the CPU to draw air across the CPU area. The PSU fan does some of that job but having the rear exhaust will reduce the temperature of hot air entering the PSU and circulating around the CPU area which should help all parts last longer.
The next most important fans for me are the front intake(s) to keep HDDs cool and give natural convection a helping hand by ramming fresh air along the case's bottom to help displace hot air.
Since you already have an exhaust (preferably at the rear of your case) your new fan should be set as an intake and sited at the front of your case.
Good luck.
Is there a specific reason in trying to maintain negative pressure? If so, why add another fan? But the best cooling configuration for case fans is front and side intake, rear and top exhaust.
I would install another exhaust fan out the back with the current one or another exhaust out the top. You haven't told us what case so really can't answer the question.
You really don't need intake. The case will draw in all the air it needs passively through the front of the case.
This is what my current case looks like. The PSU fan is a exhaust fan. The CPU fan is a down blower fan. There are also two fans on the graphics card. Depending whether the fan is an exhaust of intake fan, the fan will be installed either at the front or the back.
The most important fan is the exhaust next to the CPU to draw air across the CPU area. The PSU fan does some of that job but having the rear exhaust will reduce the temperature of hot air entering the PSU and circulating around the CPU area which should help all parts last longer.
The next most important fans for me are the front intake(s) to keep HDDs cool and give natural convection a helping hand by ramming fresh air along the case's bottom to help displace hot air.