Low cost PC chassis may come with only a single fan, typically at the rear. Early in the fan was a small 80mm fan, This gave way to larger 120mm fans. Front fans grew in popularity quickly which reduced the workload ion the rear fan. The two fans teamed up to move more air. Most recently the top of the chassis now has fan mounts where an exhaust fan can be mounted. The larger full tower chassis may use 140mm fans which and water coolers are common.
Using the Corsair Obsidian 750D as the example will make it clear why its called the Airflow Edition. Two factory installed 140mm fans front are installed along with one rear exhaust fan. The top of the chassis has lots of room for a 280mm class water cooler.
Looking close at the fan, there is a mounting frame and their is a mount for the actual fan motor. By convention air flows away on the clean side. So internally mounted rear fan has the spec label and frame against the chassis grill which which will blow air out of the machine.
The front fans are outside and they are set to blow air into the chassis. So in this situation the fans are in the same orientation as the rear fan. The water cooler however typically has internal fans that should blow air into the water cooler and out the top of the machine. Some sandwich the fans which is not aesthetically appealing.
Corsair includes the ML140 fans with the Obsidian 750D Airflow Edition which means the build will be durable. Corsair can afford to provide quality fans primarily as they can get them mass produced for them. The ML140 have rubber grommets to reduce vibration which helps the bearings on the fan to run smoothly. Corsair ML140 fans can run from 400 rpm to 2000 rpm depending on the DC voltage applied. The magnetic levitation bearings can last a long time with low vibration and clean air.
Corsair also has many models of fan for custom builds. The RGB models are popular for those who have machines on their desk instead of deskside as is typical with the full tower machines. The Obsidian 750D is larger chassis with room galore for large video cards and lots of hard disks.
The hard disk trays in the 750D also have rubber grommets to help dampen vibration. Securing the motherboard to the chassis tray with a full complement of screws minimizes vibration of the video card and peripherals.
Installing a few air purifiers can get ahead of dust which will add years to a gaming rigs service life. A 12’x12′ gaming studio should have a pair of air purifiers to make sure that the air is clean. Larger areas need larger scale air purifiers. Clean air also benefits the human operating the controller.
The large image below shows the face of the fan. Air flows to the rear of the fans which is the correct orientation. A simple way to test fan orientation is to use a small piece of paper. Improperly installed fans can result in warmer than desired system temperatures. The paper test works well with even lower cost fans as well as with higher quality fans.
PC chassis fans blow air in reverse to household fans. This has to do more with the intended purpose rather than the conventions used by box fans. Box fans are available in a very wide range of sizes and they’re often seen in ventilation systems.
PC front fans are for intake of cool air and rear/top fans should exhaust warm air. This is the high air flow idea that has been standard now for almost 20 years. The bigger fans move more air so use the largest that fit.