Computer Case Guide to Airflow, Cooling and Size

Computer case guide to airflow, cooling and size

The computer case is the housing for all the parts in your computer. On top of just looking good and having the ports you need in the front panel, the case has other important requirements. It protects the parts from physical damage that can be caused by dust or accidental hits. The case must provide good airflow to keep the components inside the case as cool as possible.

This post covers the following topics

  • Form factors and tower types
  • Cooling and airflow
  • Positive airflow
  • Noise
  • HDD and SSD slots
  • Front panel
  • Expansion slots
  • Maximum dimensions
  • Cable management
  • Design

There are a lot of different manufacturer’s when it comes to computer cases. The price range is also huge, some cases can be over 10 times more expensive than the cheapest ones. So, what is the difference between the cases, what do the expensive cases offer compared to the cheaper ones? Is it worth spending hundreds on a case when you can get similar looking one for so much less? In this post, I will cover the things to look for when buying the case for your PC build. These things are simple to understand and will benefit you a lot when browsing different cases.

Form factors and tower types

Form factor means the size, in this case, the size of the case. I have talked about from factors before, in a post about motherboards. The same common form factors that apply to motherboards, apply to cases too. The most popular case and motherboard sizes are ATX and mATX (micro-ATX). You can always place a smaller motherboard inside a larger case if the screw holes match. Usually, inside an ATX case, you can place motherboards with ATX, mATX or ITX form factor. However, if you want to be completely sure your motherboard can be screwed in the case, select both with the same form factor. Following this rule will always help you to pick the right case for your motherboard. The dimensions of the case are usually written in the ad as centimetres (cm) or in inches.

The cases are also divided into different tower types. Tower type means the dimensions of the case. The amount of drive bay slots the case has depends on the tower type as well. Below is a short explanation of the most common tower types for consumers. There are other tower types, but they aren’t that common or practical for a normal PC build. The most common type of cases used by consumers is Mid Tower.

  • Full Tower = The case is high, usually 30 inches (76cm) or more. Usually 6 to 10 drive bay slots.
  • Mid Tower = Shorter than Full Tower cases. Mid Towers are around 18 to 24 inches high (45-60 cm). Usually 2 to 4 drive bay slots, the most commonly used type of cases.
  • Mini Tower = The smallest of these three. Mini Towers height is around 12 to 18 inches (30-45 cm) and they have usually 2, sometimes even 3 drive bay slots.

Now that you have selected the size of the case for your PC, we can move on with the introduction of computer cases.

Cooling and airflow

Cooling and airflow are very important, this is something you must pay attention to when you are building your computer. Let’s first go through a scenario with air cooling, since it’s still more common (and easier) setup than water cooling. Air cooled computer’s all components are cooled with air, to make your air cooling efficient, follow the instructions below to achieve the best possible result.

The CPU cooler is the fan and heatsink connected to the CPU. There is thermal paste between the heatsink and CPU. Thermal paste conducts heat from the CPU to the heatsink. The heatsink is on top of the CPU and the fan is connected on the side, there can be multiple fans depending on the cooler model. It blows air through the heatsink to cool it down. Now we have hot air inside our case, which we need to get out as fast as possible. This is where the case fans step into the picture.

Processor cooled with air

Processor cooled with air.

The case fans job is to push hot air out and pull cool air inside the case. The case fans should be placed so that the air coming in, can easily flow through the case. The air should go through the heatsinks in CPU and GPU and then get pushed out of the case. Modern GPUs have their own fans to make the air go through the GPUs heatsink they also push the air out of the case through the expansion slot they are connected to.

To get the air flow working as well as we can, there shouldn’t be any cables hanging and all drives and any other components should be in the places they belong to. Otherwise, the cases airflow isn’t very good and the cooling of the components isn’t efficient. If possible, attach the CPU fan so, that the hot air is flowing towards the case fan, that is pushing the air out of the case. You want to get rid of the hot air and not let it stay inside longer than it has to.

Positive airflow

Another important thing is that you need to get the same amount or more air in than out. This simply means that there must be more fans pulling the air in than pushing out, or you have set the fans to different speeds to get more air in. This can be achieved with programs that control the fan speeds. Getting more air in than out is called positive air flow and you want to achieve it. On top of the better cooling effect, it helps you keep the case clean from dust. All the gaps and small holes in your case are pushing air out, so dust can’t get in from those. Most cases have dust trays in the places where you take air in to help you keep the case cleaner.

Having positive air flow is an easy trick to help you keep your computer clean and avoid dust getting into the PCs heatsinks and other components it might clog or even broke. Simply, if you have negative air flow, it means that air and dust are getting sucked into your computer from all the gaps and holes, which is obviously something you don’t want because then you need to clean your computer more often and you aren’t in control of the air flow. Dust clogging your components will affect the performance of your computer and reduce the components lifespan. When you are planning the air flow in your system, remember that hot air rises up. Depending on the case, you might not want to pull cool air in from the top, because then you are fighting against the natural air flow.

Water cooling is more expensive than air cooling, but the cooling ability of water is better than airs. Basic water cooling kits only allow you to water cool your CPU. You can always invest some more and cool your GPU with the same water loop as well. If you want to cool your GPU with water, you need to buy a water block for the GPU. The water block replaces the heatsink inside the GPU. You will also need to buy tubing and connectors on top of the water pump. You will also need fans and a radiator that cools the water in the tubes. As you can already see, water cooling your system is more complicated and more expensive than air cooling.

Processor and two GPUs cooled with custom water loop

Processor and two GPUs cooled with custom water loop.

Fans are needed in both cooling methods and they come in two different sizes. Smaller fans are 120mm (millimetres) and the bigger ones are 140mm. You can use which size fits your case better. Usually, cases come with two or three 120mm fans. Depending on the case you can fit two or three 140mm or 120mm fans in the front of the case, one fan in the back and two or three fans on the top of the case. Refer to the manual or description of your case to see what fan size will fit your cases’ fan slots.

Water cooling radiators also come in different sizes. The used sizes are 120mm, 240mm, and 360mm. Radiators need fans to cool the water and that’s why the sizes fit one, two or three fans. Water cooling components require space and all cases can’t be cooled with water because of this. If you want to cool with water, or maybe you want to upgrade to water cooling later, check that the water cooling equipment needed will actually fit in your case.


When you have an air-cooled PC, you will have more noise than with water cooling. It’s because you have more fans in your case and fans simply make noise. The amount of noise is also affected by the number and model of the fans you have. Some fans make more noise than others, but the case affects how much noise can get out. If you want your system to be as silent as possible you might want to use fans that didn’t come with the case, included case fans are usually very cheap ones and can make more noise than separately bought fans.

HDD and SSD slots

Make sure that all the drives you want or need to have in your system will fit inside your case. The cases have 2.5” and 3.5“ slots for your storage drives. HDDs fit into 3.5” and SSDs can fit both, but are usually placed in the 2.5” slots to keep space for HDDs. If your case doesn’t have many drive slots, you can always buy M.2 SSD to directly connect to your motherboard.

Slots for 2.5" solid-state drives

Slots for 2.5″ solid-state drives.

Front panel

The front panel of the case usually includes power on/off, headphone and microphone audio plugins and few USB slots. Depending on the case and it features, the front panel might include, for example, LED controls and reset buttons. Make sure the connectors in the front panel matches your needs.

The front panel of the computer case

The front panel of the computer case.

Expansion slots

Expansion slots are the removable wide metal pieces in the back of the computer case. If you add for example GPU in your system, you have to remove as many pieces as the GPU needs (in most cases two). If you are going to plug multiple devices into your system, for example, GPU, soundcard, and WIFI-card, then the more expansion slots have to be removed. Make sure that you have enough PCIe slots in your motherboard and expansion slots in your case.

Expansion slots in the back of the computer case

Expansion slots in the back of the computer case.

Maximum dimensions

Usually, the case ads have different maximum dimensions for different components. Remember to check these or otherwise, all of your components might not fit in the case at all. Below is a list of components that usually cause trouble. Verify that these components will fit inside the case.

  • CPU cooler (height)
  • GPU (length)
  • PSU (length)
  • Water cooling equipment (Radiator’s length, space for water pump)

Cable management

One of the things that new PC builders might not take seriously enough is cable management. It means that all your cables are in good order and they are easy to access later if needed. Most cases have space for cables behind the plate the motherboard was screwed in. Run all your cables from there, the ones that won’t reach when ran behind the motherboard, try to run from the sides of the case, as long as they won’t interfere with other components or mess up the air flow. You can use tape or cable ties, sometimes cable ties are included.

Cable management is something that affects a few things. First of all, it improves the air flow in your computer’s case and if you are adding or removing some components, it’s easy to make the changes when the cables are in good order and easy to access. Many cases also have tempered glass side panel nowadays, if you are getting a case with a see-through side, it’s important to make the insides look clean and well managed.


The design is not important for everybody, but I like to find a case I like visually. The case is the skin of your computer and you aren’t going to see anything else on the PC most of the time (unless you have a tempered glass side). This is why I pay attention to the colour scheme and design of the case. Some cases come with integrated RGB lights even. Finding a case that looks nice and has the needed features is fairly easy because there are so many manufacturers at the moment. Although I like to have a visually appealing case, I still focus more on the features of the case. For me, the most important thing in the case is the airflow, since good air flow will extend the life of the components and prolong the cleaning interval.

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PC Rookies is a project to share information related to mostly security related topics.

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