A fan mod is either an operation involving physical modification of a fan of some sort, or a type of case mod in which one or more fans are added, removed or replaced from a computer chassis. This write-up will focus on the latter definition.

The reason for fan modding a computer is usually to improve cooling performance (very useful when overclocking) but there are those who do it simply to improve the looks of their computer.

  • Adding more fans or replacing old fans with newer, larger and/or more powerful ones will improve cooling performance, prolonging the lifespan of your components and increasing their overclocking potential
  • Replacing old fans with new fans of the "silent" variety will drastically lower the noise output of your computer
  • A few extra blowholes in your computer's chassis will make it look cooler and more powerful
  • Transparent fans, fans with LEDs in them, and aluminum fans will improve the visual appeal of your chassis, especially if combined with some nice-looking fan guards
  • Having more case fans will introduce additional redundancy into your computer's cooling system - reducing the risk of fan failure leading to system crashes and whatnot due to overheating
  • Adding more fans or replacing old fans with more powerful ones will increase the noise output of your PC
  • Removing fans or replacing powerful fans with "silent" ones will increase the temperature inside your chassis, which is generally a bad thing.
  • If you need to make a blowhole in your chassis for mounting a new fan, you risk ruining your chassis if something goes wrong
  • Fans cost money, money you could spend on something else

Sínce removing a fan from your computer is a very simple procedure, this write-up will focus on the process of adding a new fan or replacing an old fan with a new one.

Stage one - planning, choosing a fan

As always when case modding, you should start by planning exactly what you want to do. So you want to improve the looks and/or cooling performance of your chassis. Great. Which of those takes priority? Are increased noise levels acceptable? The following are some things that are good to be aware of when planning your fan mod:

Firstly, you generally suck air into the computer from the lower/front parts of your chassis, and exhaust hot air from the upper/back parts. There are obvious reasons for this. Firstly, hot air moves upward. Second, in a typical chassis, the power supply, CPU, AGP and PCI cards will be located near the back. They are the components that generate the most heat, so you will want to get rid of all the hot air that will otherwise accumulate inside your chassis.

Second, what make and model of fan you choose are not really as important as its specifications. You will want to check the CFM (cubic feet per minute) rating - that's how much air the fan pushes. The size of the fan - 40mm, 60mm, 80mm, 92mm or 120mm - is also important. All case fans are square shaped, the "size" is in fact the height and width of the fan. As for depth, it usually varies between 10 and 40mm depending on the fan. A rule of thumb: The larger the fan, the more air it will push while making less noise, since it spins slower. For example, your average 80mm fan will push about 26-32 CFM and make 25-30 dbA of noise. At that same noise level, a 120mm fan will push between 55 and 70 CFM!

Third, if you are looking for a fan with built-in LED's, be aware that such fans generally cost a bit more and don't perform as well as normal fans. They look extremely cool, however. If you feel like it, you can of course take a normal fan and add the LED's yourself, but since normal fans aren't transparent, the effect will be greatly lessened, and adding LED's to a fan isn't easy work (I might update this wu to cover the process of doing so in more detail once I've had more personal experience with it).

Fourth, don't install more cooling power than you need. If you buy and install a 120mm, 200 CFM, 63 dbA Sunon Extreme Output fan to cool your Pentium III you will get sick of the noise within minutes if not seconds and promptly replace the fan with a quieter one - an utter waste of time and money when you could have just gone for the quieter one from the start. This is especially worth considering if you intend to attend LAN parties - maybe you can stand the noise from your rig, but if the other peeps who sit near you at the party can't, you may return from lunch, a shower, or a nap to find that your computer has been fan modded in a most destructive fashion, without your consent, while you were away.

If you're not sure how powerful a fan you will need, or what the correct balance between noise and cooling performance for your system might be, consider buying fans that automatically adjust their speed depending on system temperature. These fans are a bit pricey, but it may be worth it for the peace of mind and sheer coolness factor of having "intelligent" fans in your PC.

Finally, it's extremely wise to mount particle filters in front of any and all intake fans. If you don't, a lot of dust will get sucked into your chassis, forcing you to periodically vacuum it or risk your fans failing due to accumulation of dust. In the worst-case scenario, your CPU fan would get clogged with dust and cease functioning, resulting in a complete and catastrophic system failure.

Stage two - installation

Installing a case fan is usually very easy. Simply hold the fan in place using one hand while using your other hand to attach it using a screwdriver and regular fanscrews (will have been included with the fan when you bought it). However, if you have to make a new blowhole in your chassis in order to accomodate the new fan, things can become a great deal more complicated. I'll leave it to you to figure out how to drill a hole of the right size in the side of your chassis - you can probably find some hints in my write-up on window modding, which deals extensively with the subject of making holes in computer chassis.

Important note: Make sure you put fan guards over any fans that are exposed to the outside of your computer chassis. Not only does this greatly reduce the risk of foreign objects being caught in the fan (resulting in grave damage to both fan and object), it also reduced the risk of someone who doesn't know any better getting their fingers chopped off (though only very powerful fans will actually chop off fingers, it will still hurt a lot to get stuck in them).

Once installed, the fan has to be connected to the computer's power supply somehow. Most fans come with either a 3-pin or a 4-pin female Molex connector. Many come with both. The 4-pin connector, you connect to one of the male 4-pin connectors provided by your computer's power supply. The 3-pin connector, you connect to a free fan header on your motherboard - the wires are for +12V (red), ground (black), and possibly RPM monitoring (yellow), respectively. If your fans support RPM monitoring (you can tell by the presence or lack of the yellow cable), and your motherboard supports it (most existing motherboards and all new ones do), you can use a a program such as MBM (Motherboard Monitor) to monitor the operational status of your fans.

If your fan only has a 4-pin Molex connector (the same kind that's used for providing power to, among other things, your hard drives), then the fan does not support RPM monitoring (the yellow wire from the 4-pin connector is NOT for RPM monitoring and unfunny things will happen if you try to use it for that purpose). Some fans have a 4-pin connector and a 3-pin one with only the yellow wire leading to it. In this case, you need only use the 4-pin connector for the fan to work, but you can optionally enable RPM monitoring by plugging the 3-pin one in as well.

Important note: Some motherboards will refuse to boot completely, or sound warning beeps during POST, if there's no fan connected to the "CPU FAN" header on the motherboard, or the fan connected does not support RPM monitoring. Keep this in mind in order to avoid nasty suprises.

Stage three - all done? Conclusion

Having put everything together and connected the new fan(s) to your motherboard or PSU, all that's left to do is to power the computer up, make sure that the fan is spinning (in the right direction) and check for any change in temperatures. On most motherboards, you can check the CPU and chassis temps in the BIOS. If your chassis temp is above 35 degrees C or your CPU temp is above 60, it's generally a good idea to consider getting better cooling.

Important note: If your computer refuses to boot up or even power on after installing the fan, there's probably a short-circuit and your power supply is trying to prevent you from toasting your PC. Promptly disconnect the fan and take appropriate steps to identify and correct the problem.

In conclusion, fan mods are not particularly hard to do but can take a fairly large amount of planning and searching the web if you're not sure about what type of fan you need. A fan mod is, however, one of the most effective ways of improving your computer's cooling, or lowering the amount of noise it puts out. The only real disadvantage is that you usually can't have both of these things at once.

Thank you for reading. If you enjoyed reading this, you may also enjoy reading my other writeups about case mods. They're all linked below.