How Much Static Pressure is Needed for a Fan

The dominant factor at present in the world of refrigeration is a greater number of fins per mm2. This represents a further restriction that the fans must overcome to improve the temperatures of the refrigerated component in question. The problem is that there is no optimal measuring stick that frames restriction with static pressure, so users get lost trying to understand what they need and above all, how much static pressure is needed for a fan?

The number of models of heatsinks and radiators is increasing. The improvements come with a dropper, it is true, but that does not prevent new products from being launched every so often and it is modified from the number of fins, such as their arrangement, shape, height, thickness and many more parameters such as tube welding or heat pipes.

How Much Static Pressure is Needed for a Fan

That is why there is no general static pressure optimization guide, how to recommend what is right for so many combinations of heatsinks, radiators and fans? We are going to shed a little light on this topic through some guidelines.

Performance vs loudness vs price

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It is the first topic to deal with before we get down to business. We have to be clear that a fan can be focused for three different uses: introducing or removing air from the chassis, cooling a radiator or heatsink and finally being a fan that tries to combine both.

Each type of fan will have a different performance depending on where it is placed, a higher or lower loudness for the same parameters and above all totally different prices. Fans that only need to move air move a lot of flow (low static pressure), need low RPM, their loudness is very low and their price is also lower.

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By cons and logic, high performance fans have high static pressure, low flow, high RPM and higher loudness. This assumes that a fan to move air is not going to be used in radiators or heatsinks and vice versa for obvious reasons, but how to differentiate them?

The ideal would be to see your P / Q chart , but as almost no manufacturer offers it, we will have to keep the key values and this is where we will hook with the main topic of the article.

What is the minimum static pressure we need?

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As in everything, there has to be a minimum value that we can make a standard among the community, and the main value to look for is precisely static pressure. Fans that move a lot of flow will have very low static pressures and conversely we will find fans with a lot of static pressure and little flow at the same RPM.

That is, these two values are inversely proportional: the maximum pressure value of a fan corresponds to its zero flow, and the maximum flow value will result in zero static pressure.

Therefore, and with this very clear, we need to know the minimum restriction to discern the recommended lower static pressure and here one more factor comes into play: the FPI or fins per inches, translated as fins per inch.

noctua_nf_a12x25_pq_compared

We simply have to know that the more fins per inch a heatsink or radiator has, the more restriction the air passage generates. The problem is that heatsinks do not usually offer this value because it is very low, whereas in radiators it is a differential factor for performance, since a higher number of FPI means both greater restriction and higher performance.

Therefore, we will have two minimum static pressure values:

  • Minimum static pressure for heatsinks , including the densest in FPI.
  • Minimum static pressure for radiators .

In the first case, very little is actually required to overcome, as a rule, the restrictions of these, and therefore we speak of an average value of 1 mmH2O . This should be more than enough not only to make the air flow smoothly, without generating too much noise due to the restriction and it will also allow us to get more performance out of the heatsink compared to other fans with less pressure.

In the case of radiators the requirement increases. The fin density is much higher and these are much smaller, leaving smaller gaps between them, making it difficult for air to pass through. Therefore, the minimum static pressure rises to 1.5 mmH2O for any self-respecting fan and taking into account that we can go from the 11 FPI to the 30 FPI that exists today.