Ensuring your computer receives sufficient cooling with PC case fans isn’t rocket science but it can be tricky. Sure, you could take the “maximum power” approach of shoving as many fans as possible into and onto the case, but that’s far from ideal. There needs to be rhyme or reason to the setup or else it becomes something wholly inefficient. We break down the fundamentals of air cooling your computer so you can avoid a Chernobyl-like meltdown.
Case fans and ventilation
Every fan features a cubic feet per minute (CFM) rating, which measures of the volume of air it moves in a minute. The greater the CFM, the more air a fan moves. To properly air cool your computer, you need have enough case fans to push or pull air into and out of the case. More case fans means higher total CFM and more air being moved through your computer.
Just be mindful of the noise levels as fans can generate quite a buzz. To avoid making your computer too loud, use fewer or quieter fans. Also, flashing multi-color lights shouldn’t be the main feature of your case fans.
Use proper fan positioning
Air travels one way through a fan, in one side and out the other. By changing the direction a fan is mounted, it can act as either an intake or exhaust. You should also heed the placement of the fans. Air should travel in clear path through the case. Generally, you want the case fans in front of the case drawing in air while the fans at the rear blow air out.
If your case has vents at the top, they should be placed as exhaust fans because hot air will rise. Side-mounted fans should be used for intake, though they often don’t have air filters. To prevent dust issues, you can custom fabricate your own filters.
Dust is the silent killer
Speaking of dust, you want to make sure that your computer remains as dust free as possible. Otherwise, all the airflow in the world won’t help much to cool down your components. To reduce dust in the case, ensure that the air going into the case first passes through a filter. Many cases have removable filters that can be cleaned by a quick rinse. Just be sure to actually clean the filters once in a blue moon. By leaving filters dirty or covered in dust, you reduce airflow and cooling power.
Aside from fans and vents the other major points of ingress include the many small gaps in the chassis and adjoining pieces. You can’t really control airflow at these points unless you want to put caulking or sealant in your case.
Positive v. negative air pressure
Optimal air pressure with a computer case is one of the most discussed and debated topics in computer cooling. In simple terms, a computer case can either have:
- Positive pressure – The case fans push more air into the case than then pull out, so there is more air pressure inside of the case.
- Neutral pressure – Air pressure in the case is equal to air pressure outside of the case. Difficult to attain unless you leave the case open.
- Negative pressure – More air is being pulled out of the case than being pushed in, creating a vacuum.
To determine pressure, total the CFM of all the intake fans and CFM of all the exhaust fans. If the intake CFM is greater, then you have positive pressure. If exhaust CFM is greater, then you have negative pressure. Neutral would be when intake and exhaust CFM are equal.
In a perfect scenario, you’d have neutral pressure with an enclosed case because no dust would be sucked in. Negative pressure would mean that air is being sucked into your case from all the tiny gaps you can’t control and don’t have filters on, which means less efficient cooling over time. Aim for slightly positive pressure, with slightly higher intake CFM than exhaust CFM. This way, the air that enters your case goes through a filter first.
Final Words
When building your computer, be sure to configure your cooling system with the principles outlined above in mind. Otherwise, you may end up with a toaster oven of a computer. Just be sure to avoid those tacky LED-equipped case fans in the office.
Originally published Sept. 2015. Updated Feb. 2021.
your first picture is wrong, fan intake is the open side on 99% of fans. Your negative pressure graphic is not likely as you would never exhaust out the front. A single exhaust fan with no intake fan is negative pressure. A single intake fan with no exhaust fan is positive pressure. Of course there’s the CPU and GPU coolers as well as the PSU playing into it. Different flow affects dust build up just as much as the case and house itself. You want as close to a laminar flow as you can get, which just means as smooth and unobstructed as possible.
You really could have spent a little more time on this to make it easier to comprehend for the beginners.
Hi illuxionary!
Thanks for the feedback. The first image of the fan has been replaced. As for the pressure graphics, the arrows are supposed to represent pressure rather than airflow. In hindsight, using another method to represent air pressure would’ve been better.
Question here, how can you find out the cfm rating of the stock fans that come with a computer case? My case came with 4 fans, 1x 80mm and 3x 120mm but I can’t find any info on the cfm rating of the fans.. Is there any software what I can install to get these ratings as most software just gives you if the fan is working or not and at what rpm..
The case I have is the NZXT Lexa Blackline
Thanks
Mike
good post about pc cooling fans
I have a NZXT H500 case, it has 1exhaust on the back and 1 on the top aswell and i have a NZXT kraken x62 for cpu liquid cooling and the radiator is mounted at the front with 2 intake fans. So my question is, should i flip the top fan to be an intake and leave the one on the back as an exhaust? Or just make them both exhaust?
The NZXT H500 and 510 series cases are specifically designed to be negative pressure. That is why all the perforated side plates and back plates are that way and the fans are mounted to be exhaust only. It works pretty well stock. Reversing would be bad as the 2 are so close together they would cancel each other out in a small area and give most of the case NO airflow.
Lots of youtube videos about people monkeying with them to try to get better cooling / higher flow with mostly poor results as even higher flows don’t actually do much to temps (esp GPU temps as the stock config negative pressure draws cool outside air right across the GPU’s own fans).
If you do add intake fans in front there is limited ventilation for them to bring in much air since the front panel is solid, and it will mess up the negative pressure design unless you upgrade to higher cfm exhaust fans too (and since NZXT is also a fan maker these cases have AER f120 fans instead of generic cheapo fans).
I had an expensive gaming computer built and I noticed they installed the cpu liquid cooler radiator w/ (2) 120mm fans over top of the (3) 120mm case fans at the front panel. Does this configuration compromise the intake cfm’s?
There was only (1) 120mm exhaust fan mounted at the rear panel. This means I have positive pressure happening in my case. Should I add additional fans at the top of my case to help with proper air flow?
Imo this is hard to measure just by calculation because most of the cases would provide some restriction to the front intake due to the dust filters and stuff on the front panel which makes front fans less efficient – while at least the rear fan has no restriction since there are no filters on the back.