Fan specifications explained

Fans are one of the least interesting parts of a new PC build, but it’s important to choose the model that not produces the right amount of air movement, but also how quiet it is at doing its job.

There are fans for CPU coolers, standard case ventilation and also for watercooling radiators. There are different types that conform to the PC standards of 80mm, 92mm, 120mm and the lesser used 60 and 40mm varieties.

There are three values stated by most manufacturers in regards to their blowers, which are CFM, static pressure and noise output. Read below for details on each.

CFM

CFM, or cubic feet per minute is a way of explaining the fans air output in statistical form. For example, a 20 CFM fan pumps less air than a 30 CFM fan. This gives you an inkling of the fans maximum possible air output for the specified voltage.

The CFM values written on fans are measured when the fan has no resistive force acting against it (e.g. a fan grill, or CPU cooler fins) and hence doesn’t give you a real world figure, but does give you the maximum possible rating for the fan – think car top speed.

CFM is therefore tied to the static pressure of the selected fan.

Static pressure

Static pressure is the measure of how powerful the fan is when put up against a resistive force. For example, a high static pressure fan will stay closer to its rated CFM when behind a fan grill, or a watercooling radiator. Static pressure becomes very important for watercooling setups as a high CFM with low static pressure could easily pump less air when compared to a lower CFM fan, but with higher static pressure. Static pressure is normally described as inches of water or in millimetres.

If the static pressure is low and the resistive force that the fan is blowing through is too high, then the fan will stop and becomes useless. A perfect example is if you were to put your hand over the outlet of a fan (your hand is the resistive force) the CFM drops as the fan has to work harder in order to pump the same amount of air; a higher static pressure fan in this scenario will see less of a CFM drop.

Static pressure is an oft missed statistic on fans which may lead you to consider why they have neglected this important figure about the fan.

Noise output

Accustic noise output is described in decibels (dBA) and gives you the quietest that the fan will be during operation. It’s the quietest possible, as the fan will have no resistive force when measured and when you add resistance, the fan has to work harder and the object that is resisting will product its own noise; a fan behind a fan grill is louder than when the fan is left in free air.

What this figure doesn’t measure is the tone of the outputted noise. A low pitch sound is more