Intake and exhaust fans

[twistffa]

I have 2 fans on my computer. One at the top and one at the back. I have an AIO liquid cooler. The fan at the back is sitting on the radiator. Which one should be intake and which one should be exhaust??

 

[Barty1884]

The optimal two-fan setup is front intake, rear exhaust. But it will vary depending on the case in question.

With the setup you describe, the front should pull cool air from the environment, and exhaust through the Rad.

If you use the AIO fan as an intake, you'll increase the temps to the rest of your components.

 

[ThomasLeong]

I have a different opinion to this. Similar to a car's rad, the fins are meant to cool the hot intake from the engine (cpu), and circulate the cooled liquid back to the engine. Therefore, I think blowing external cool air direct to the rad helps more than drawing hot air from the rad. The front fan(s), normally meant to draw cool air into the case and exhaust through the rear, imo, gets the air drawn in dissipated to other parts of the case reducing its effectiveness.

So, imo, drawing hot/warm air from the case making for negative pressure in the case is better. We all know that a vacuum cannot exist in the case, so external cooler air will naturally be drawn in from all other vents to fill the 'vacuum', and with the help of the rear fan(s) blowing in to help the rad fins, the case and other components should remain cooler internally overall.

I say this from experience. I have a 19" 2U case with only 2 x 80mm fans in the front, factory installed to exhaust outwards. I am using a Radeon Pro WX4100 gpu which exhausts its hot air to the top, back into the case. The cooler is a Noctua NH-LX12 with the 120mm fan blowing air downwards to the cooler fins. Initially, with this setup, the case, with all sides closed, was warm to hot to the touch, especially in the area just above the WX4100.
I reversed the 2 x 80mm fans to expel hot air from the case (there is no fan at the rear with this 2u mATX case). Cool air naturally flowed in from all other vents of the case to replace the 'vacuum' created. The area of the WX4100 immediately cooled to the touch compared to previously. I have run this pc with no temp problems outdoors for a function under a 3-sided tent with no air conditioning from 12noon to 12 midnight with afternoon temps in high 36C - 40C (i live in the Tropics near the Equator).

I am now a subscriber to negative pressure in the case versus positive pressure.

ThomasL