Chassis fans or case fans are the most common things found on a modern desktop pc. They can actively cool the insides by blowing out air and/or taking in cool air. Case fans usually come with the Chassis and can be monitored within the BIOS or by a program.
The computer case fan usually has a 80mm size; they are installed on the side of the case to blow out hot air. There are also other computer cases that can handle using a 120mm fan but are only widely used by computer enthusiasts. There are also cases in which a computer case doesn’t use a fan; water-cooling or passive cooling can be an option for people who have problems with the fans having too much noise.

The casing of a modern desktop is usually transparent on the left side; this will permit viewing of peripherals and devices installed. Computer case fans is always a requirement to make sure the heat inside is regulated and must be of safe levels for normal operation, a very hot processor or video card can result to programs crashing and hardware failure.
The case fan is not the only fan in the chassis, there are also fans installed on the processor, power supply unit and the optional devices such as the graphics-processing unit. Fans can be used in tandem with a Heat sink to greatly minimize the heat level.

When installed with a grill fan, the noise levels can marginally improve on a computer case fan. The decibel level of a regular ball bearing fan is about 27 dB, and can be regulated by fan control devices or in the motherboard bios. Manufacturers have made the fan fancier by installing LED lights and UV-reactive plastic to match and decorate cases. Multiple fans can be connected to a computer case; there is usually a built-in y-splitter to make sure there are still enough 4-pin Molex connectors for other devices or peripherals.