Choosing the right fan
Cooling fans are available in wide range of sizes and shapes (small barrel-types, large axial type fans). The most common fan sizes fall in the 70mm to 140mm range, but fans as large as 230mm are more popular now. Fans with a diameter of 120mm are typical in newer cases. You need to choose the fan which has high air flow (which is measured in cubic feet per minute (CFM) or cu ft/min). This details or information are printed on the package of your product. Fans vary in speed, blade shapes, and color also. Some fans even come with a built-in LED light to give you PC case some extra beguiling. The larger fan can usually spin at a lower speed and still move plenty of air without making much noise. Look for lower volume levels and high reliability. Fans are usually pretty inexpensive. Some of the more popular manufacturers are Cooler Master, Evercool, Deep Cool, Corsair, and Thermaltake.
Power Connection
Most Cooling fans come with the standard connector of some sort but the modern system will typically use 3-pin or 4-pin dedicated fan headers. For example, MOLEX 4-pin peripheral connectors are used. Make sure to check what type of fan connector you need before buying your fan. The analog 3-pin or MOLEX connectors provide power to the fan to make it rotate. The four-pin connectors are digitally controlled and let the PC to alter fan speeds. Many motherboards have 3-pin or 4-pin fan headers that are placed at different locations around the board. Fan headers will look like a row of 3 or 4 pins on the motherboard, often denoted with a label printed on the board.
Maintain Positive Pressure
When adding fans to a PC, maintaining a positive pressure within the case can prevent dust from being sucked into any open holes. To maintain positive pressure, you need to have a higher combined CFM for the intake fans than the exhaust fans. Most fans have small arrows embossed on their frames that show the direction of the air flow. When mounting, point the arrow towards the inside of the PC for intake, and arrow towards the outside for exhaust.
Installing a fan
To mount a fan, hold it up to the mounting position so that the holes for screws with the holes in the PC case. While holding the fan in place with one hand, use four screws to tight it securely(shown in the picture above). Some PC case has plastic friction clips which are easy to fit the fan. After this attach the fan to fan header. The headers are keyed to ensure a proper connection. 4-pin headers will work with 3-pin fans. You can’t control the speed of the fan here. But 4-pin fan connections allow your PC to change the fans speed. Usually, the fan runs on a lower speed to reduce noise and increases speed when more cooling is needed (you can hear the running speed of the fan in some laptops because it needs more cooling)
