Featured is the  Thermaltake V200 with tempered glass RGB edition comes with 4 fans, 3 up front and 1 behind. The blue arrows indicate air intake and the red arrows indicate exhaust. Note, the internal parts are not included with the case. 

The air flow is not shown for the power supply on the bottom of the case. It looks like the air intake comes from inside the computer and exhaust going out the back.

Why does Temperature matter?

Before power, the temperature inside of a computer will be the same as the ambient or room temperature. Turn the computer on and components will dissipate heat inside the computer case. Hot air rises but in the enclosed computer case, air has nowhere to go.

As the computer runs the temperature inside the computer will continue to climb from the dissipated heat of the components. There are many factors including software, and overclocking that will cause the computer to produce excess heat. As temperature inside the case increases, components like the CPU will degrade in efficiency and if too hot, fail.

Therefore, we need a way of either cooling or moving the hot air inside the case. An air conditioning unit would help at least lowering ambient temperature.

What is a Fan?

So we need to understand why we are trying to cool/move air. A fan is an apparatus with rotating blades that moves a current of air. To reiterate, a fan only moves air and does not cool it.

Fans come in different shapes and sizes specifically rated by a manufacturer. Here are the main specifications and factors to consider when choosing a case fan.

How many wires 3-pin versus 4-pin (PWM)

A regular 3-pin fan has wires for power, ground and a tachometer. The tachometer pin feeds information to the motherboard and can be viewed by software. The 4th pin on some case fans allows for Pulse Width Modulation (PWM) allowing speed control to the motherboard and can be software controlled.

Fan Speed

Revolutions Per Minute (RPM), how many rotations the fan will make in one minute. The higher the RPM the faster the spin, and usually, noise level will increase.

Computer Case Fan Size

There are so many fan sizes, the most common sizes are: 80mm, 92mm, 120mm, 140mm and 200mm. Fan size is related to airflow, the larger fan will push more air as opposed to a smaller one running at the same RPM. This is great for lowering noise levels.

How do you measure fan size? The size of fan you need will be determined by the size of the fan fitting position in your case. The sizes are shown as measured along any one of the fan’s four sides.  Lastly, do not measure the length of the blades.

The most common thickness (depth) of the fan, is 25mm (1 inch) , although there are smaller depths such as 15mm or 10mm. 

An alternative way to measure fan size is to measure the distance between the fan mounting screw holes. Measure the mounting holes horizontally or vertically and not diagonally. See the following table. 

Screw hole spacings and fan sizes

72mm between screw holes: 80mm fan size
83mm between screw holes: 92mm fan size
105mm between screw holes: 120mm fan size

Fan Noise

Most of the manufacturers in the industry use dBA to measure sound. The sound can be measured by a dBA meter.

A decibel dB is a logarithmic unit to measure the ratio of power. We are concerned with sound or in this case, fan noise. Sound decibels are decibel Sound Pressure Level or dB SPL.

A-weighting dB(A) or dBA uses an International standard from the IEC and various national standards relating to the measurement of sound pressure level (SPL). The A-weighting curve has been used for environmental noise measurement, and is a standard in sound level meters (dBA meters). The higher the rating in dBA the more noise it puts out. See the noise table, taken from ASHA American Speech-Language-Hearing Association.

dBA  Scale Examples:

130 dBA = jackhammer

120 dBA = jet plane takeoff, siren, pneumatic drill

112 dBA = maximum output of some MP3 players, rock concert, chainsaw

106 dBA = gas leaf blower, snow blower

100 dBA = tractor, listening with earphones

94 dBA = hair dryer, kitchen blender, food processor

91 dBA = subway, passing motorcycle, gas mower

70 dBA = group conversation, vacuum cleaner, alarm clock

60 dBA = typical conversation, dishwasher, clothes dryer

50 dBA = moderate rainfall

40 dBA = quiet room

30 dBA = whisper, quiet library

0 dBA   = threshold of hearing

Fan Noise Dampener

There are many factors that affect noise from a computer. More fans, additional noise while insulation dampens the noise. Few cases have insulation, with the exception
of those marketed as silent cases. However, you can customize a computer case configuration with insulation to suit your level of noise output. 

There are aftermarket kits for insulation and fan dampening. The kits feature several sheets of sound-dampening lining that you attach to the inner walls of a case. They can be cut, shaped, and folded to fit a case’s internal dimensions. See the Recommended Parts below.

Cubic Feet per Minute (CFM)

CFM – is the total air volume that a fan can move at max speed.  To convert airflow in Cubic Feet per Minute to cubic meters per hour (m³/h), multiply the CFM figure by 1.7. Useful for telling a fan’s air performance.

Fan Controller

Fans running at high speeds can be loud. If your system is loaded with the latest CPU, GPU and power supply, it may be running hot. Try to make the best of the situation with the assistance of a modern fan controller. 

A controller makes it easier to monitor the temperature of your PC components. Tweak your fan speed without overheating the system.
Things to consider:
Aesthetics – There are some very cool looking controllers on the market, make sure the controller meets your minimum needs.
Controls – Some controllers have a dial to control the speed of a fan. Others controllers provide LED screen displays, and some have a touchscreen. Make sure that the controller supports 4 pin PWM so that you can control the speed.

High Air Flow vs Static Pressure Fan

High airflow fans push as much air as possible, while static pressure fans push air through/around obstacles. Radiators and case meshes are becoming the norm in PC builds, which is where a static pressure fan will be used. The difference between the two designs are the blades.

Static pressure fans are more efficient than high airflow fans moving air through radiators, case meshes, and dust filters. High static fans effectively tackle resistances, and are suitable to thick radiators as opposed to low static pressure fans. Should you swap out fans if you’re using airflow models on radiators?

For performance a static pressure fan will work the best, if something will block partial airflow. 

Fan Airflow Direction

The sticker facing you is the back of the fan, apply power and the air will be blowing towards you. For air intake, the fan sticker will face the inside of the case. Some fans may have two small arrows engraved into their case – one arrow indicates airflow direction, and the other (at 90°) blade rotation.

Computer Case Power Supply

There are many arguments about where to locate a power supply on the top or bottom. Locate where ever is convenient and make sure that the air flow to the intake of the power supply is filtered and unimpeded. I have seen many power supplies overheat and fail, due to clogged fans from dust.

Case Fan Ventilation

Do not overload a computer case with all the fans on the intake and similarly on the exhaust. Creating the best balance is the key to optimal design of computer case cooling fans. Use some common sense, have an equal number of fans for intake and exhaust with preferably the same fan ratings.

Dust

Dust is a silent crippler and cannot go unnoticed, so the intake fans must be filtered. Used panty hose are a perfect substitute if you don’t have filters for the intake. Watch for dust accumulation around the optical drive, HDD and around components. A big build up means it is time for an adjustment and or more filters.

Check the intake filters every day or once a week. Regular cleaning and filter maintenance will keep your computer running like a champ.