How to Build a PC - Selecting Case Fans
Once you have chosen your PC case, you can start planning out the cooling configuration for your system. Most cases will ship with at least a few fans, which should give you adequate cooling for a typical system. For those of you who are not satisfied with “adequate” cooling, keep reading and we will discuss aftermarket case fans and how to determine what is best for your rig.
Let’s first discuss some of the main specifications and factors to consider when choosing aftermarket case fans for your rig.
3-pin versus 4-pin (PWM)
A regular 3-pin fan has wires for power, ground and tach (tach relays information to your motherboard or software, like RPM). The 4th pin found on some case fans allows for PWM (Pulse Width Modulation) control, which allows your motherboard, or fan control software to adjust the speed of your fan.
Left: A 3-pin fan plugged into a 4-pin fan power header on a motherboard.
Right: a 4-pin fan cable with the extra blue "PWM" wire.
Revolutions Per Minute (RPM) tells us how many times the fan will make a complete rotation in one minute. The higher the RPM the faster the fan is spinning, and in most cases, the louder the fan is going to be.
120mm case fans tend to be the most popular size of fans in modern PC cases, but you will find many sizes such as 80mm, 92mm, 140mm, 200mm and beyond. Fan size is closely related to airflow, in that larger fans will push more air than smaller ones while running at the same RPM. What this means is that larger fans can spin much more slowly than smaller ones, while still pushing the same amount of air, which is great for lowering noise levels. The one drawback from larger fans is with compatibility, since many cases are only setup for support of 120mm and 140mm fans.
Another way to compare fans is to look at their noise level which is usually measured in dBA (decibel level). The most obvious way to compare the noise level of different fans is to look at their specs on the box, however this can be deceiving since different manufacturers may test fan noise in a variety of different ways. For example, one does not usually know how far away from the fan the dBA meter is sitting, and what the background noise in the testing room is like. I know that many fans that we have tested here at Corsair have been very optimistic with their specifications, and because of this, I would recommend resorting to third party reviewers to get the most honest comparisons.
Cubic Feet / Minute tells us how much air the fan is capable of moving. For a typical case fan, this is the most telling spec when it comes to the fans cooling performance.
An example of a high airflow (CFM) fan from Corsair.
Static pressure is measured in units of mmH2O. The higher this number is, the more force the fan can exert on an object. Static pressure is most important when you are mounting your fan to something that will block some of its airflow, such as a water cooling radiator, CPU heat sink, or an HDD cage where the fan will be obstructed by the HDDs.
An example of a fan from Corsair that has high static pressure.
Measured in Amps (A), tells you how much power the fan will use. To convert this figure to maximum wattage, you will want to multiply it by the maximum voltage the fan supports. For example our AF120 Performance Edition fan has max power draw of .13A and max operating voltage of 12v. — .13a x 12v = 1.56 Watts.
In addition to making your system perform better, adding aftermarket fans can also be a way to further customize the look of your system. Corsair’s aftermarket fans come with interchangeable colored rings so that you can color coordinate with your systems motherboard, graphics card, or memory. Colored LED fans are also available for anyone who wants there system to light up. Below you can see some examples.
Static Pressure versus Airflow
Corsair makes things easy and offers two different types of case fans, one specializing in airflow (AF series) and another specializing in static pressure (SP series). Both types are optimized for different types of use. The AF series is best to use when you want to move air efficiently and have little to nothing blocking the fan. The SP series is the better option if you need to push air through an object, such as a water cooling radiator, CPU heat sink, HDD cage, or any other type of obstruction. Both AF and SP series fans come in “quiet” and “performance” editions. Below, you can see some examples of how the Performance versions compare with the Quiet versions.
Now that you understand what fan specs mean, you should have a pretty good idea of what to look for. Other manufacturers may not have their fans labeled as airflow and static pressure, but a quick look at their specs should give you a good idea of what they are good for.
In the next part of our “How to Build a PC” series, we will talk about picking out the optimal CPU cooler.