A Guide to Intake/Exhaust Fans and Airflow on Your PC

Case Fans And Airflow Featured Image

It’s no hidden secret that the key to keeping your computer’s components cool is to use fans. High-end graphics cards include them by default, and while processors don’t come with fans directly stuck onto them, failure to add a heatsink after installation will cause heat-related shutdowns in mere seconds!

While you might not have heat-related issues, you might find your system getting a little too warm when performing intense system activities. In this case, it might be worth investigating the possibility of adding intake and exhaust fans to your computer.

What Are Intake and Exhaust Fans?

When a heatsink removes heat from corresponding components, the hot air tends to linger around and warm up the inside of your PC. This means the “old air” is being reused by the fans to cool the system, which isn’t ideal! The key, therefore, is to add fans that either get rid of this ambient heat or bring in fresh, cooler air to be used. This is the role of intake and exhaust fans.

computer-airflow-fans

As for their differences, it’s very simple: Intake fans brings fresh air into the PC, while exhaust fans kick stagnant air out. In coalition with one another, they can help keep your ambient temperatures down. Rather than attaching themselves directly to components, intake and exhaust fans attach to your computer’s case. You may find grills with four screw-sized holes on each corner around your case. These are places where you can install intake and exhaust fans.

They draw power by being plugged in to three- or four-pin sockets on the computer’s motherboard. If you’re looking to get fans for your own PC, make sure you understand where these sockets are and how many of each you have on your motherboard.

The Case for Airflow

While simply adding these to your PC may help reduce temperatures, we can use our heads and put them in strategic spots on our PCs to get the most out of our cooling!

By using one intake and one exhaust fan, we can perform the following:

  1. Fresh air is brought in via the intake fans.
  2. The fresh air mingles with the system, supplying it with cool air. This cool air is used by heatsinks to extract heat from components and becomes heated air as a result.
  3. The heated air is pushed out of the computer via exhaust fans.

What we have is a simple intake -> extract -> exhaust system, where a computer is consistently fed cool air while heated air is expelled. This is called a computer’s “airflow” and is a great way to make the most of your system’s fans.

The best way to imagine airflow is to think of a stream of air beginning from the intake fans and ending at the exhaust. As such, we want this flow of air to cross over as much of the PC as possible. When implementing intake fans (or purchasing a case with them pre-installed), they go on the front of the PC where there’s less outside obstruction. This means we put the exhaust fans on the back or top of the PC, so the airflow travels through the PC, picks up heat, and carries it out of the system.

computer-airflow-diagram

Getting Fans

So now we know how these fans are used to create an airflow within a system. However, if you look for PC fans to put onto your computer case, you’ll see many semi-confusing statistics being mentioned. What do they mean?

computer-airflow-specifications

Intake or Exhaust?

You may notice a lot of fans don’t state whether they’re intake or exhaust fans. This may be because they can be either! Not only will the fan work regardless of what side you install toward the case, but on the fan unit itself, it should show you which way it pushes air. This means you can buy two of the same fan. Just install one so it draws air in and the other so it pushes air out.

Case Compatibility

Not all fans are made the same size! If your case has spots for fans to be installed, make sure to measure the horizontal distance between the two slots for the screws and get a fan that matches that size. If you measure the distance between two adjacent screw holes at 120mm, a 120mm fan will fit. Also, ensure the fan you’re buying isn’t a CPU cooler.

Here are some common case sizes and fan sizes to match:

  • Specialized SFF (Small Form Factor) Cases – 120 mm fans or smaller (80 mm) fans in extremely small cases.
  • Mini ITX Cases – 120 mm fans are most common. Some ITX cube cases may come with a single 200 mm fan for intake as well.
  • Micro ATX Cases – 120 mm and 140 mm fans are most common, but 140 mm and 200 mm fans may appear as well.
  • ATX and Extended ATX Cases – 120 mm and 140 mm fans are most common, and a few cases may even support two 200 mm fans.

RPM

The RPM (Revolutions Per Minute) defines how fast a fan spins. The higher this number, the faster the fan will spin.

CFM

The CFM (Cubic Feet per Minute) of a fan defines how much air it can shift in a minute. The higher this is, the more air the fan will push in, or out, of your system. In this case, the more the merrier!

dBA

This is the decibel statistic. It represents how loud the fan can get. If quiet fans are a big consideration for you, make sure to pick a fan with a low dBA.

Pins

Most fans come with a three-pin connector, which will fit into a three-pin fan plug on a motherboard. However, if your motherboard supports four-pins, you can try four-pin fans instead. The extra pin adds speed control to the fan, while three-pins typically work as fast as they can. Just remember that three-pin fans can still work on four-pin connectors – it just won’t be controllable.

Positive or Negative Pressure?

A positive pressure fan setup refers to when you have more fans doing intake (bringing in air) than doing exhaust (pushing out air). A negative pressure fan setup is the opposite, where you have more fans doing exhaust than intake. For most scenarios, a positive pressure setup will be better than a negative pressure setup, so keep this in mind when setting up your fans.

Static Pressure or High Airflow?

There are two main types of case fans you can buy: static pressure fans and high airflow fans.

A static pressure fan is a low-CFM case fan that pushes air much stronger than a high airflow fan, making it ideal for use with liquid cooling radiators and intake from panels that don’t have as much free airflow.

A high airflow fan is exactly what it sounds like – a high-CFM case fan that pushes a lot of air very fast but not particularly well against resistance. A high airflow fan is best as an exhaust to get the hot air out of your PC as fast as possible, or as an intake where you have a mesh front panel.

For the Fans

When a PC gets hot, using fans is a simple and cheap way of getting the temperatures back down again. However, with a little bit of care, you can get the most out of your money by ensuring the fans create an airflow within your system, using a combination of intake and exhaust fans to do the job.

Instead of desktop fans, if your laptop’s fan is making a loud noise, here is how to reduce the fan’s noise.

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Christopher Harper Christopher Harper

I'm a longtime gamer, computer nerd, and general tech enthusiast.

2 comments

  1. Wouldn’t taking off the side panel of your PC case help more in heat dissipation than a bunch of case fans?

    1. Technically, yes! You’d still want an intake fan so you’re getting a draft of fresh air through the PC, but leaving the case side open allows the heatsinks to expel the heat outside the system by themselves.

      However, at the same time, keeping the side panel open exposes the PC to new problems, such as an increase in dust settling on hardware; pets, bugs, and children getting into it; spillages; and accidental knocks and bumps. I know some people who swear by an open case, but if objects, animals, and liquids getting into your PC is a real risk, it’s best to pick up a cheap fan and cover the precious hardware from danger!

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