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Airflow 101: Setting Up Your Fans and Keeping Your Computer Cool

Don't forget to check out other 101 articles:
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Power Supply 101


Welcome to Airflow 101! If you've come here because you're new to PC Building, or if you're a veteran who just wants to see if there are any ideas you can use, you're in the right place. I geared this as being a basic rundown, so if there are some parts missing, don't worry, this isn't meant to be an all-encompassing guide.

How air flows through a computer's chassis is one of the least considered things by many pc builders when it comes to assembling their PCs. Many builders think that core temperature is the only important measurement when it comes to the computer and its cooling capabilities. However, the ambient temperature inside the case is just as important, if not more so, since it affects the entire computer. Not paying attention to how you set up your computer's fans can severely degrade your system's ability to cool itself. The good news is, that the basic rules for good airflow remain the same, no matter what components you have, your case, or where your case is.

Rule #1: Cold Air In, Hot Air Out

Now, you may be thinking that this is a stupid rule, but let me assure you, this is the most common error people make when setting up their cooling system. Usually, the error comes when installing a fan, the builder simply isn't paying attention, and the fan is installed so that it blows air in the wrong direction.

Another common mistake is to have radiator over an intake fan. To many beginning watercoolers this seems to be ideal since it brings cold air through the radiator; however, this has the adverse effect of putting hot air into the case, bringing the ambient temperature up. It's a much better idea to have your radiator placed at the top or rear of your case (See Rule #3), so cooler internal air can be used to cool the loop.

Rule #2: Have More Exhaust Fans Than Intake Fans (Negative Pressure)

This is important to remember because having more intake fans (Positive Pressure) than exhaust can lead to stagnant air. Stagnant air leads to higher internal temperatures since there aren't enough fans removing the heated air from the inside of the case. In general, positive pressure doesn’t cool as well as negative pressure will. That said, one of the benefits of Positive Pressure is that less dust will enter the system.

Negative pressure provides the best cooling performance for enthusiast (often heat intensive) builds. It builds on natural convection and works with graphics cards.
[Note] This is less important (if you have a computer with mesh paneling) than it used to be with the advent of computer cases with mesh paneling, since there tends to be more paths for air to escape from the case.

Rule #3: Exhaust Out the Top and Rear, Intake Through the Bottom and Front

One of the most important things to remember about cooling: heat rises. That said, it makes the most sense to place your exhausting fans near the top of the case while your intake fans stay near the bottom.


How air should flow through your case

There are several reasons why this is the best method:

- As stated before, hot air rises so cool air is near the bottom of your case, while the heat from your computer is above it.
- The rear of the computer is usually confined, so it’s a bad place to have intake fans.
- You don't want hot air exhausted out the front and onto you.

Rule #4: Dust Kills


This one should be obvious, you really don’t want dust in your system. Dust is the silent killer of computers, it will stifle your heatsink’s ability to cool your chips and if you are using fan filters, clogging them won’t do anything good for your airflow.
So what can you do?

Did you know that by elevating your computer only 6 inches off the floor you can reduce your dust intake by up to 80%? Most of the dust in our lives starts out in the air and ends up on the ground. So if you let your computer sit on the floor, especially on carpet (You should be ashamed!), you’re just asking for your PC to fill up with dust.

Practice good cable management. Messy cables give dust an anchor to attach itself to, and they just don’t look good. To fix this you should do two things:
-Buy a good case. Seriously, don’t skimp on such a crucial part of your PC, a nice case has good cable management features, and it will look that much cooler when you show off your computer to your friends.
-Buy a good, modular, power supply. Here is a secret about good cable management: It’s really easy if you only have the cables you need. Look in your computer. Do you have the exact amount of cables you need, or do you have a bunch of cables that just don’t know where to go?

Let’s look at a few examples:

Would you rather show this to your friends?

Or this?

If you say the second one, you made the right choice (but that one is mine, so you can’t have it). While both of these computers have about the same number of components, the latter one will always stay cleaner and look better because it has good cable management.

While I still clean my computer every couple of months, I know I never have to worry about dust build up becoming an issue.

Rule #5: The Quality of Your Fans Determines the Quality of Your Airflow


It is important to remember that more fans does not guarantee better airflow.

What you should look for are high quality fans with a high CFM (cubic feet per minute) airflow. More fans give you more potential generators of turbulence, which can keep hot air from going where it should, lingering in the case instead of leaving. Less fans with a higher CFM will result in a much more constant and smooth airflow.

Another important thing to consider when buying fans is the quality. Obviously this can be hard to gauge if you can’t see it in action, but purchase fans from companies you recognize, as off brand fans may be cheaper, but often perform much worse.

The last thing that is important to note is static pressure. This is a fan’s ability to overcome resistance. One common cause of major resistance is a radiator. Look for fans with high static pressure ratings when purchasing fans for radiators, you will get much better performance even if the CFM is lower (within reason) than another fan.


Well, you made it to the end! Hopefully you can walk away from this with a much more in depth understanding of airflow and what you need to do in order to keep your computer running as great as day one. It is important to note that as you become more experienced, you may end up doing things differently, and that's perfectly fine. This tutorial is only meant as a basic guideline, and it may not work in all the situations.

If you have any questions or feel that I missed something, feel free to ask or comment so I can update this guide to be most beneficial to you, the readers. Airflow is just as much of an art as watercooling, and it takes dedication, patience, and careful thought to make it work to your advantage.

Happy Building!


I sourced some of my images and knowledge from Extremetech and wouldn’t feel right if I didn’t include a link to their article. If you have the chance, consider checking it out as it has additional comments that I didn’t put in my tutorial.

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