Hello,

I am in the process of trying to quieten/streamline my headless Linux (Openmediavault) server and was wondering whether I really need both an intake and an exhaust fan.

Here is my build spec:

G1840
MSI B85M-E45 m-ATX
12GB DDR3 (2x4GB and 2x2GB)
1x64GB Crucial M4 SSD
2 x 2TB Samsung F4 HDD
1 x 1TB Samsung F1 HDD
1 x 6TB WD Red HDD
Superflower Golden Green 350w PSU (Gold Rating)
Xigmatek Midgard Tower with 1 x 120mm exhaust fan and 1 x 140mm intake fan

Do you think I really need both or could I lose one?

The biggest gain is the first fan, as you are able to pull or push the hot air out. In most cases the second fan is worth it, the gains in temps are not as big as the first fan, but in most cases the gains are still enough to make it worth it, but each setup is different, my suggestion is try with one and see your temps, see if everything is with in tolerance and decide from there. Personally i like more fans at lower rpms than few fans a higher rpms, but again each setup is different so the gains or noise that you will generate vs the temps will be different.

Some links that might be useful for you to check out,
Bittech The Big Air Cooling Investigation
LinusTechTip Case Fans - How many should you have?

Only considering cooling performance, an intake and exhaust fan (2 fans) is the minimum recommendation and the best bang-for-buck. As more fans are added, there are diminishing returns. Although, 3-4 fans may help if you're going for more fans and slower fan speeds.

A couple more considerations:

- You'll want positive internal case pressure (more intake than exhaust airflow) to reduce dust buildup.
- Your intake airflow should equal or exceed the airflow of internal fans (cpu and gpu coolers, radiators etc) to make sure they're fed with cooler outside air, rather than recycled hot internal air.
- Your case is not airtight, so exhaust happens automatically with positive internal pressure.

So, if you're just installing 1 fan, make that an intake. If 2, test whether 1 intake + 1 exhaust works better in your system than 2 intakes. Could very well be that 2 intakes is better, if your case allows 2 front intake fans, try that. Remove unused PCI slot covers to allow air to better flow out freely. Also, most stock fans that come with cases are mediocre at best, you might want to look into new fans if you want both decent cooling and silent operation. Good options are ones with high static pressure, such as Be Quiet! Silent Wings 3, Noiseblocker NB-eLoop B14, Phanteks PH-F140, Thermalright TY-14x etc.

I want to push back on the idea that positive pressure alone reduces dust. The intake fans move just as much dust into the case as any intake flow. Dust is only reduced by filters, and filters add restriction. Restriction of air flow, means you need to run the fans faster.

Exhaust fans are more effective - pulling air through the case is easier than pushing it. Nature abhors a vacuum, and so lowered pressure draws air via the path of lowest resistance.

My typical set up is to start the rear / top exhaust first, and run it at a slightly higher RPM. If needed, the front / bottom intake starts at slightly higher temperatures. With a hot video card in a conventional set up, I would go to a top fan (if the exhaust is on the rear). In a case like the Silverstone FT-05 with it's vertical video card position, it is easy to stick with the stock (180mm?) intake fans. So, when the natural flow is easy, just having intake fans are fine.

I think it is better to have more low speed fans, rather than fewer higher RPM fans.

Generally, balanced airflow is good overall, but slightly positive is preferable to negative.

Exhaust fans are more efficient when dust is not an issue.
The reason they are more effective is that thay suck air through all openings of the case (except the parts used for exhaust). That reduces the restriction and thus increase the flow.
The downside is that one needs to keep track of where all these openings are:
Close those that can be expected to recirculate heated air into the case. (All openings in the rear that are not directly used for exhaust, for example.)
Open up those near parts that need cooling, to create an airflow past them.