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.
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.