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Decoding the Fan Specification

CFM, RPM, Static Pressure, Explained

Fan specification can be hard to decode, learn what you need to know before picking a computer box, and installing your new computer fans.

Episode #4-29 released on April 5, 2014

Fans, more specifically computer fans, can be very difficult to decode, and a lot of information is a mystery to people looking to purchase the correct fan for their computer. This episode will help you out with some of the common information you will find on a computer fan box, and the correct way to buy fans, and install them in your computer.

First, how do we calculate the correct size of a fan required?

Most fans come into 80mm, 92mm, 120mm, 140mm, 200mm, and 230mm sizes. 80mm, and 120mm being the most common fans in some computer boxes. For an 80mm fan, the holes from one corner to another will be exactly 72mm apart, for the 120mm fan, it will be 105mm apart.

Should I use static pressure fans?

Unless you are pumping air through a radiator you are not required to use static pressure fans, however, the CFM will be higher as a result in using them.

What is CFM, and how do we calculate it?

CFM stands for cubic feet per minute. It is the amount of air the is circulated by a fan. It can be calculated like this: (fan diameter)2 * (air pressure)2 / (100 * 28.51875) = air flow.

Should I have negative, positive, or neutral pressure in my computer box?

Negative air pressure will force dust into your computer from any crack, positive air pressure won't, but some of the air will not flow correctly, so going positive or negative pressure in your build is not a good idea. Better to have as much air coming in, as leaving the box to allow the hotter inside air to escape.

What size should my fans be?

If you already have your computer box, then it may be too late. If you are in the market for a computer box, determine the task requirement first. If you are doing high performance tasks, planning on playing video games, or need a computer that makes very little noise, bigger is better. Bigger fans have a higher CFM, and need less RPM in order to achieve this, in return they make very little noise. For computers where the tasks will be light, or the noise output is not an issue, you may consider using fans as small as 80mm, but I personally would not recommend any smaller due to the high output of modern processors and graphics cards.

What direction is the intake of a computer fan?

Installing a fan is imperative, but short of plugging it in, and feeling the wind blow, which direction does the air flow? From the open end to the closed end.

I have my computer box, I have my fans I need, in what direction should air flow?

There is a fairly good reason why computer boxes have air flowing from the side and front in, and out through the back, and top, and this is because it respects many of the laws of thermal transfer of heat. Hot air rises, and using this to your advantage makes your computer cooler. Front and side fans should always intake air, and the rear and tops should be for exhaust. I personally leave an 8 to 12 inch space behind my computer to allow it to breathe, and this in turns allow my computer rig to be cooler as a result.

Host : Steve Smith | Music : Jonny Lee Hart | Editor : Steve Smith | Producer : Zed Axis Productions

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