FAQ: What to consider when choosing a fan

There have been as many posts asking “What is the best X fan?†where X can be replaced by silent, powerful, radiator, and other conceivable categories. In fact, there has been as many of these types of threads as there are stars in the sky since noobs have not figured out how to use this wonderful invention called search. Anyways, this FAQ will hopefully be able to answer any and all of such questions. Please note, these FAQ is for 120mm case fans since that is what everyone is using nowadays, but can for the most part be applied to smaller or larger fans as well.

Like people, case fans come in all sorts of sizes, noise, shapes, and styles. Some are loud, some are shiny, some have fancy lights, some are ugly, and most are over priced. As more and more people join the computer enthusiast community, more and more fans flood and saturate the market. How do we know which type of fan we want? Well first, here are some things we should understand first when considering a fan:

1.RPM â€" RPM stands for revolutions per minute or in layman’s terms, how many times a fan blade can make a full circle in a minute. Usually as RPM increases, noise level and airflow follows suit.
2.dBa â€" dBa stands for decibel adjusted, which means the noise power calculated in dB or decibels. Scientifically, this is a unit of measurement for voltage or some type of intensity, but all we need to know is it tells us how loud the fan is.
3.CFM â€" CFM stands for cubic foot per minute or how many cubic feet of air can the fan generate per minute. In a perfect world, this means that for every elapsed minute X cubic feet volume of cool air is coming into your chassis or X cubic feet volume of hot air outside the case
4.Static Pressure â€" This is probably a technical specification that you will rarely find advertised on the market, since to the average consumer, it doesn’t mean a damn thing to them. Unfortunately, this is due to ignorance not lack of practical use. What static pressure means is how much pressure a fan generates when it is running. So how does that affect us would probably be the question most normal consumers would ask. Well, basically the greater the amount of static pressure generated, the greater amount of air the fan will be able to push or pull through obstacles, such as a filters, heatsinks, or radiator fins. A good way to check how much static pressure is to put sheets of paper in front of the fan. The more sheets of paper the fan blows up the higher the static pressure.

So we have four very important technical specifications how are they related to each other and to my purchase? Well, price notwithstanding, here is how they relate or do not relate to each other.

1.The higher the RPM (how fast the fan spins) is usually directly proportional to the dBa (noise level) and CFM (airflow).
2.dBa and CFM are determined by more than simply RPM. Other factors like fan motor technology, the amount and shape of fan blades, and type and condition of lubricant are all factors of dBa and CFM, but this is something that will be elaborated on later.
3.Even though RPM directly affects dBA and CFM, dBa and CFM are not directly related. Depending on the motor technology, type and condition of lubricant used by the fan, and amount of fan blades, you can have high CFM with low dBA or low CFM with high dBa.
4.Static pressure is not related to either dBa or CFM but rather it seems, to the fan design and the turbulence it creates. It is also important to note that static pressure leads to resultant CFM when a fan is placed on a heatsink, radiator, or filter.

With those relationships in mind, we now have to consider what type of technology is behind the fans we want. Currently there are about 5 different types of general technology used when making a fan (info is cited from wikipedia):

1.Sleeve â€" Use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 50 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age
2.Ball â€" Use a sealed bearing containing steel balls against which the axle rotates. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 50 °C.
3.Rifle â€" Similar to sleeve bearing, but are even quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
4.Fluid â€" Have the advantages of near-silent operation and high life expectancy (comparable to ball bearing fans). However, these fans tend to be the most expensive.
5.Magnetic â€" Also called maglev fans, the fan is repelled from the bearing by magnetism in order to spin.

While companies may give their fan technology fancy names such as SFD or Hydro Wave, all fans are based off of those basic designs, just improvised and improved.

Ok, so enough about what kinds of fans exist. How do I know which type of fans I want? Also, talk is cheap and anyone can cite information from the Internet. Why would I trust you? To address the latter valid point, in my quest for optimal air cooling at acceptable fan noise, here are the fans that I have met on my long journey:

- ADDA/Lian Li
- Aerocooler Turbine
- Antec Tri-Cool
- Akasa Amber Series Ultra Quiet fan
- Arctic Cooling
- Cooler Master
- Delta AFB
- Everflow Aluminum
- Everflow Radwing
- Noctua
- Nexus
- PAPST Vario
- Panaflo Hydro Wave
- Rosewill
- Sanyo Denki Sans Ace 1011
- Scythe Kaze
- Scythe S-Flex
- Scythe Slipstream
- Sharkoon Golf
- SilenX (both commercial and server)
- Silverstone F-series
- Sunon Triple Blade
- Thermaltake Thunderblade
- Yate Loon (both Petra’s and standard)

So what does this mean aside from I am an idiot who wasted tons of money on fans? It means that I can honestly provide an owner’s experience with a large variety of fans.

When choosing a case fan. We are normally choosing it for the following reasons:
1.Chassis cooling
2.Radiator cooling
3.Heatsink cooling
4.Pure silence

Chassis cooling can be further split into two sub-categories… intake and exhaust.

1.Intake - When we are talking about intake, we usually have to consider dust and noise level. It does not matter if the fan is on the front or the back. If a fan is sucking air into the case, dust is going to come in. For this reason, most case manufacturers usually install some sort of filter in addition to a fan grill. This means a fan needs enough static pressure to pull air through a filter while still maintaining enough airflow to keep as near an internal chassis air pressure as possible so that there are no hot spots or areas of trapped hot air. The fan must also be at our desired noise level.

-Noctua
-EMB Papst
-Scythe S-Flex
-Akasa Amber Series
-Antec Tri-Cool
-ADDA/ Lian Li
-Yate Loons

2.Exhaust â€" When shopping for an exhaust for our case, we usually have only a fan grill attached as the only obstacle for a fan. Basically, the airflow is relatively rampant and unrestricted. This makes it simple for us as static pressure is no longer a factor and we only need to consider CFM, dBa, and overall intake airflow.

-Scythe Slipstream
-Noctua
-Scythe S-Flex
-Nexus
-Aerocooler Turbine
-ADDA/ Lian Li
-Cooler Master
-Yate Loon

When shopping for fans to cool radiators, the main consideration is static pressure. A fan with lower CFM but much higher static pressure will cool much better than a fan with higher CFM but crappy static pressure. Never has this been more obvious when comparing a Scythe Slipstream fan to a Scythe S-Flex fan. Theses are the following fans I have discovered with a good amount of static pressure:

-Sanyo Denki Sans Ace 1011
-Panaflo Hydro Wage
-EMB Papst
-Scythe Kaze
-Noctua
-Scythe S-Flex
-Antec Tri-Cool
-Yate Loons

Case fan specifications for heatsinks are remarkably similar to case fans for radiators, because it is pulling air through a ton of aluminum or copper fins. The only additional consideration here would be case clearance.

Pure silence condition is usually for HTPC setups where heat is not too much of an issue. This is where you look solely at the dBa to the exclusion of all save price.

-Noctua
-S-Flex
-Nexus

Now of course these are just simple generalizations of what to look for when shopping for a fan. The fans I listed are my personal preference. The simple answer is there is only a best fan when you have set very concrete conditions of what type of fan you are looking for where as many factors have been eliminated, conditions like following:

-Quietest fan possible regardless of airflow â€" Noctua NF-S12
-Best radiator fan possible regardless of noise â€" Delta (the fattest one)

Without specifying what exact conditions of case fans you are looking to achieve, even then most people will still only be able to limit it down to a few fans and from there it is up to you as the consumer to experiment. This is because even with stringent or specific conditions, people have different definitions of what is loud, what is sufficient airflow, and other difference in opinions in factors. At this point, the consumer has to take the range offered to him and figure out the best available one from there and that will be HIS best X fan!