For a cooling fan, first decide the size, airflow, and pressure (how much heat must be removed, how crowded the air path is, where the operating point lies); then look at bearings and life (sleeve, ball, fluid dynamic bearings, and temperature); next, speed control and electrical (voltage, speed control wire, speed feedback, noise); after that, deal with mounting and maintenance (the airflow resistance of guards and filters, dust, testing in the real unit). This article focuses on axial cooling fans inside cases, control cabinets, and equipment; ionizing blowers, liquid cooling, and large plant fans are outside its scope. The 4 stages:
Stage ①｜Size, airflow, and pressure: the airflow needed, airflow resistance, the operating point, size and hole positions.
Stage ②｜Bearings and life: sleeve, ball, fluid dynamic bearings, temperature and life.
Stage ③｜Speed control and electrical: voltage, speed control wire, speed feedback, noise.
Stage ④｜Mounting and maintenance: guards, filters, dust, testing in the real unit.
This article starts from the point where you already know the equipment needs a cooling fan. Each stage below covers: what to do, what the public sources say, and what Jiahon can help with; the data from each source and the basis are in the “Notes” at the end. This is the general case; individual cases still have to be judged on their own.
Figure 1: The four stages of choosing a cooling fan. ① Size, airflow, and pressure — airflow: how much heat must be removed; pressure: how crowded the air path is; size and hole positions: must match the equipment; at the end of this step: size, airflow, and pressure settled. ② Bearings and life — bearings: sleeve, ball, fluid dynamic; temperature: read life together with ambient temperature; speed: lower speed lasts longer; at the end of this step: bearings and life settled. ③ Speed control and electrical — voltage: DC or AC; speed control: 4-wire pulse width modulation; speed feedback: 3-wire pulse signal; at the end of this step: speed control and electrical settled. ④ Mounting and maintenance — guards and filters: add airflow resistance; dust: settles on heat sinks; testing in the real unit: measure temperature and check the margin; at the end of this step: mounting and maintenance settled. (Illustration, not to scale.)
Stage ①: Size, airflow, and pressure — first work out how much heat must be removed, then see how crowded the air path is
What to do:
First work out the heat to be removed: the heat generated by the equipment and the allowed temperature rise; these two figures determine the airflow needed, which is then multiplied by a margin.
Look at the air path: where components are packed densely or the fin gaps of the heat sink are narrow, pressure matters more than airflow, so choose a fan with high static pressure.
Look at the operating point: the actual airflow is where the fan’s airflow–pressure curve crosses the equipment’s airflow resistance curve; do not look only at the maximum airflow in the catalog.
Size: 92, 120, and 140 mm are common; the size and hole positions must match the equipment.
Parallel fans increase airflow only when resistance is low; makers do not recommend series operation.
What the public sources say: A motor maker’s selection example (undated) says: find the airflow needed from the heat generated and the allowed temperature rise, with an example of 450 W and a 20 °C rise giving about 0.5 m³/min; the calculation must account for internal pressure loss, and the example assumes the airflow at the operating point is fifty percent of the maximum airflow; multiplying by a safety factor of 2, the airflow needed is 1.00 m³/min. Another page from the same motor maker (undated) says: where mounting density is high, use a fan with high static pressure. Another fan maker’s technical document (January 2026) says: the P-Q curve shows how airflow changes with static pressure; the operating point is the intersection of the fan performance curve and the system impedance curve; an operating point in the stall region may cause noise and unstable airflow; in parallel, total airflow increases only when system impedance is low, and the maximum static pressure is the same as for a single fan; series operation is not recommended. A technical forum article from an electronic components distributor (April 2021) says: airflow is the airflow at zero pressure, and maximum static pressure is the pressure at zero flow — two different conditions. An online encyclopedia entry says: common sizes are 92, 120 (common), and 140 mm, and square 120 and 140 mm fans are used where cooling demands are high; when the fin gaps of a heat sink are narrow, static pressure matters more than airflow; the size and mounting holes must match the equipment used (Notes, Table 1).
What Jiahon can help with: the specifications below were all read from the text of the product pages on October 13, 2026; for anything the product page does not state, please inquire.
Cooling Fans / Thermal Paste: the product page is a brand introduction with series links (fan series, thermal paste series); it does not state size, airflow, pressure, or hole positions, so please inquire.
PWM Cooling Fan Series: the product page has three sizes, 80, 120, and 140 mm, with these speed ranges and static pressures: 80 mm (including a 15 mm thin version) 200 to 3000 rpm, 1.9 to 2.35 mmH₂O; 120 mm, one model 1050 rpm or 200 to 2000 rpm, 0.5 to 1.85 mmH₂O, and another model 200 to 2100 rpm, 2.75 mmH₂O; 140 mm, one model 200 to 1700 rpm, 2.4 mmH₂O, and a 16 mm thin version 120 to 1800 rpm, 1.31 mmH₂O. The product page does not state airflow, so please inquire.
AC Fan: the product page states 160×160×50 mm, 200 V AC, single unit; airflow, pressure, speed, and hole positions are not stated, so please inquire.
Cooling Fan Guard: the guards on the product page are named by fan size, in 4, 5, 6, 7, 8, 9, 11, 12, 15, 17, 18, 20, and 22 cm; it explains that a 9.2 cm fan takes a 9 cm guard; the hole positions and opening sizes are not stated in the product page text (the description refers to a dimension drawing on the detail page, which this article did not look at).
Stage ②: Bearings and life — read life together with temperature
What to do:
Bearing type: sleeve bearings, ball bearings, and fluid dynamic bearings each involve trade-offs: purchase cost, noise, life, and whether they can be mounted horizontally.
Temperature: temperature has a large effect on life; check at what ambient temperature the life figure in the data sheet was given, then compare it with the temperature inside the equipment.
Speed: at lower speed, life is usually longer and noise lower.
Environment: look at dust and water protection ratings and the high and low temperature range together with the expected life.
Have spares or a replacement plan; life figures are examples under stated conditions, so check the conditions.
What the public sources say: An online encyclopedia entry says: sleeve bearings are generally cheaper than ball bearings, quieter at low speed early on, but may become noisy with use, and less durable at higher temperatures because the contact surfaces wear and the lubricant dries out; ball bearings do not have the orientation limits of sleeve bearings and are more durable at higher temperatures; fluid dynamic bearings are almost silent and long-lived but more expensive; an example of life at 50 °C is about 30,000 hours for sleeve bearings and over 60,000 hours for ball bearings. A technical forum article from an electronic components distributor (April 2021) says: bearing type has a major effect on life, noise, and the mounting positions that can be used; lower speed is usually associated with less noise and longer life, and the temperature of the working environment strongly affects life. A fan maker’s selection tutorial (undated) says: selection must weigh expected life, protection rating, and the ability to withstand high and low temperatures (Notes, Table 2).
What Jiahon can help with: below are the bearings and noise stated on the product pages; none of these four pages states life in hours or the corresponding ambient temperature, so please inquire, and include the temperature inside the equipment and the life required.
PWM Cooling Fan Series: the product page states a new-generation positive-pressure fluid dynamic bearing (the page’s wording), with operating noise reduced below 0.3 Sone; it also states a 6-year warranty — a warranty is not the same as life in hours.
AC Fan: the product page states long-life bearings, without stating the bearing type, life in hours, or ambient temperature, so please inquire.
Stage ③: Speed control and electrical — how it is powered, how its speed is controlled, and how you know it is turning
What to do:
Voltage: DC or AC, rated voltage, and allowed range must match the equipment’s power supply.
Speed control: 4-wire fans have a speed control signal wire and can use pulse width modulation; 3-wire fans do not have this wire.
Speed feedback: 3-wire fans have a tachometer pulse; some have a locked-rotor alarm signal; the controller must be able to read it.
Noise: noise drops quickly as speed drops; catalog noise is measured with no resistance, and will differ once the fan is installed in the equipment.
Power and noise: confirm the power budget and the upper noise limit the equipment can accept.
What the public sources say: A fan maker’s selection tutorial (undated) says: 4-wire fans use pulse width modulation for speed control; 3-wire fans have a tachometer pulse, two pulses per revolution; some 3-wire fans have a locked-rotor signal that outputs high when the impeller is locked; confirm the power budget and the acceptable upper limit of sound pressure. An online encyclopedia entry says: a 3-pin connector carries ground, power, and the speed signal; a 4-pin connector adds a pulse width modulation wire, and it works when plugged into a 3-pin socket but loses speed control; fan noise is roughly proportional to the fifth power of speed; fans can slow down when temperatures are not high. A technical forum article from an electronic components distributor (April 2021) says: the rated voltage is more often the middle of the voltage range; noise is often measured in an anechoic chamber under free-air conditions, and actual noise is affected by the combination of fan and equipment, with lower speed generally giving less noise (Notes, Table 3).
What Jiahon can help with: below are the electrical and speed control details stated on the product pages; for DC fans’ rated voltage, speed feedback, and noise figures not stated on the product pages, please inquire, and include the equipment’s power supply and controller interface.
PWM Cooling Fan Series: the product page states PWM speed control support, with standard 3-pin and 4-pin connectors; a daisy-chain function lets up to 4 fans share one PWM signal and run at the same speed; there is a 0 dB mode (stopping completely at low load). The rated voltage is not stated on the product page, so please inquire.
AC Fan: the product page states 200 V AC, and explains that AC fans run directly on industrial AC power without a voltage conversion module. Frequency, speed control, and speed feedback are not stated, so please inquire.
Stage ④: Mounting and maintenance — guards, filters, and dust all eat into airflow
What to do:
Guards: the proportion of the fan opening blocked by the guard is a major factor, adding noise and airflow resistance; keep the guard some distance from the fan.
Filters: a filter with large openings has low resistance and clogs less easily, but cannot stop larger particles; small openings are the opposite.
Openings: the equipment’s vent area is recommended to be at least one and a half times the fan frame size.
Dust: dust settles on heat sinks and acts like an insulating layer, reducing heat dissipation; filters are often added at air inlets.
Vibration damping: resilient mounting pads can be used between the fan and the case.
Testing in the real unit: once chosen, install a sample in the equipment, measure the temperature, and confirm there is enough margin.
What the public sources say: Another technical forum article from the electronic components distributor (from April 2021, with page information marked August 2025) says: the proportion of the fan opening blocked by the guard is the main factor, and the noise and static pressure loss caused by a guard may be large; guards of bent wire may be quieter than guards of stamped sheet metal; filters cause a pressure drop and reduce airflow, and filters with large openings resist airflow less and clog more slowly but let more particles through; it recommends keeping the guard a little away from the fan; vent area should be at least one and a half times the fan frame size; using temperature monitoring with speed control to keep airflow at the lower end of what is needed can slow filter clogging; resilient mounting pads can reduce the transmission of vibration. A motor maker’s technical data page (undated) says: filters cause large pressure losses, while finger guards cause almost none. An online encyclopedia entry says: filters are often added at air inlets to keep out dust, which insulates heat sinks and reduces heat dissipation. A fan maker’s selection tutorial (undated) says: it recommends actually installing a fan sample in the system for testing, to confirm there is enough thermal margin (Notes, Table 4).
What Jiahon can help with: below are the guards and maintenance details stated on the product pages; fan filters, vent sizes, and vibration-damping mounting pads are not stated on the product pages, so please inquire.
Cooling Fan Guard: items include three kinds of guard — silver chrome-plated iron, silver 304 stainless steel, and black electrocoated iron; the product page states protection rating IP40 (preventing entry of solid foreign objects of 1 mm diameter and above); welded metal wire; screws not included and must be bought separately. Wire diameter, open area ratio, and effect on airflow are not stated on the product page, so please inquire.
AC Fan: the product page reminds you to replace the fan as soon as possible when abnormal noise (bearing wear) or a clear drop in speed appears, to avoid the equipment overheating and shutting down from insufficient cooling.
When you need to match a type, please prepare six items first: the equipment’s heat generation and allowed temperature rise, how crowded the air path is and its airflow resistance, the ambient temperature and required life, the power supply and speed control, the upper noise limit, and the mounting dimensions and hole positions. You are welcome to contact Jiahon.
On the SMT / EMS line: equipment fans, filters, and product cooling
Fans and filters inside equipment. One AOI maintenance specification in our engineering files lists “cleaning fan filters” as a fixed maintenance item; when the fan filters of control cabinets, industrial PCs, or camera light sources clog, temperatures rise and the equipment may crash or misjudge. Put the maintenance interval into the equipment PM schedule (Stage ④ of this article).
Cooling in reflow ovens and ovens. The cooling zones of reflow ovens and the circulation in ovens all rely on fans; a drop in fan efficiency changes the oven temperature profile; for measurement and verification methods, see IPC-7530.
Fan assembly in finished products. When an EMS builds servers, power supplies, and industrial control systems, fans are assembled parts: for direction, connectors, wire fixing, and appearance, acceptance follows IPC-A-610; for wire harnesses, see IPC/WHMA-A-620. For the general construction of fans, see Computer fan.
Notes: sources and exceptions
The following is for those who need to verify; skipping it does not affect the method above. Where your data sheet, the fan maker’s selection data, or measurements on the equipment differ from this article, they take precedence.
Sources for each stage
| Source | Where it is used, and where it comes from |
|---|---|
| Source 1 | Stages ① to ④: sizes, fin gaps, bearings, life examples, connectors, noise and speed, dust. From: the online encyclopedia entry on computer fans (edited by many people; the content changes) |
| Source 2 | Stages ② to ④: items to weigh, 4-wire and 3-wire, power budget, testing in the real unit. From: a fan maker’s selection tutorial (undated; maker material) |
| Source 3 | Stages ① to ③: definitions of airflow and static pressure, effect of bearing type, rated voltage, how noise is measured. From: an electronic components distributor’s selection and application guide (April 1, 2021; technical forum article, distributor material) |
| Source 4 | Stage ④: guards, filters, vents, vibration damping. From: the same distributor’s article on noise, guards, and filters (from April 1, 2021, with page information marked August 21, 2025; distributor material) |
| Source 5 | Stage ①: P-Q curve, operating point, parallel and series. From: another fan maker’s technical document (version January 23, 2026; maker material) |
| Source 6 | Stage ①: heat generation calculation example. From: a motor maker’s selection calculation page (undated; maker material) |
| Source 7 | Stages ①, ④: high-density mounting, pressure loss of filters and guards. From: the same motor maker’s technical data page (undated; maker material) |
| Jiahon data | “What Jiahon can help with.” From: Jiahon product pages |
Table 1｜Size, airflow, and pressure
| Item | Content |
|---|---|
| Common sizes | 92, 120 (common), 140 mm; square 120 and 140 mm used where cooling demands are high; size and mounting holes must match the equipment (Source 1) |
| Fin gaps | The narrower the fin gaps of the heat sink, the more static pressure matters relative to airflow (Source 1) |
| Definitions of airflow and static pressure | Airflow is the volume of air moved at zero pressure; maximum static pressure is the highest pressure that can be produced at zero flow (Source 3) |
| P-Q curve | Shows how airflow changes with static pressure; the main basis for selection (Source 5) |
| Operating point | The intersection of the fan performance curve and the system impedance curve; falling in the stall region may cause increased noise and unstable airflow, so choose a model whose operating point is in the stable middle section of the curve (Source 5) |
| Parallel and series | In parallel, total airflow increases only when system impedance is low, and maximum static pressure is the same as one fan; series not recommended (Source 5) |
| Calculation example | Heat generation 450 W, allowed temperature rise 20 °C, about 0.5 m³/min on the chart; operating point airflow assumed to be fifty percent of maximum airflow, safety factor 2, need 1.00 m³/min (Source 6) |
| High-density mounting | Where mounting density is high, use a fan with high static pressure (Source 7) |
Sources: 1, 3, 5, 6, 7
Table 2｜Bearings and life
| Item | Content |
|---|---|
| Sleeve bearings | Generally cheaper than ball bearings; quieter at low speed early on, may become noisy with use; less durable at higher temperatures, because contact surfaces wear and lubricant dries out (Source 1) |
| Ball bearings | No orientation limits of sleeve bearings; more durable at higher temperatures (Source 1) |
| Fluid dynamic bearings | Almost silent and long-lived, but more expensive (Source 1) |
| Life example | At 50 °C, sleeve bearings about 30,000 hours, ball bearings over 60,000 hours (Source 1) |
| Effect of type | Bearing type has a major effect on life, noise, and usable mounting positions (Source 3) |
| Speed and temperature | Lower speed is usually associated with less noise and longer life; working environment temperature strongly affects life (Source 3) |
| Items to weigh | Expected life, protection rating, ability to withstand high and low temperatures (Source 2) |
Sources: 1, 2, 3
Table 3｜Speed control and electrical
| Item | Content |
|---|---|
| 4-wire fans | Speed controlled by pulse width modulation (Source 2) |
| 3-wire fans | Tachometer pulse, two pulses per revolution; some have a locked-rotor signal, outputting high when the impeller is locked (Source 2) |
| Connectors | 3-pin is ground, power, and speed signal; 4-pin adds a pulse width modulation wire, works in a 3-pin socket but loses speed control (Source 1) |
| Noise and speed | Noise roughly proportional to the fifth power of speed; fans can slow down when temperatures are not high (Source 1) |
| Rated voltage | More often the middle of the voltage range, not the upper limit (Source 3) |
| How noise is measured | Often measured in an anechoic chamber under free-air conditions; noise once installed is affected by the combination of fan and equipment; lower speed generally gives less noise (Source 3) |
| Power and noise | Confirm the power budget and the acceptable upper limit of sound pressure (Source 2) |
Sources: 1, 2, 3
Table 4｜Mounting and maintenance
| Item | Content |
|---|---|
| Guards | The proportion of the fan opening blocked by the guard is the main factor; the noise and static pressure loss it causes may be large; guards of bent wire may be quieter than stamped sheet metal guards; keep the guard a little away from the fan (Source 4) |
| Filters | Cause a pressure drop and reduce airflow; large openings mean low resistance and slow clogging, but more particles pass (Source 4) |
| Comparison of pressure loss | Filters cause large pressure losses; finger guards almost none (Source 7) |
| Vents | Vent area at least one and a half times the fan frame size (Source 4) |
| Speed control and filters | Using temperature monitoring with speed control to keep airflow at the lower end of what is needed can slow filter clogging (Source 4) |
| Vibration damping | Use resilient (rubber-type) material for mounting hardware to reduce vibration transmission (Source 4) |
| Dust | Filters often added at air inlets; dust acts like an insulating layer and reduces heat sink dissipation (Source 1) |
| Testing in the real unit | Actually install a fan sample in the system for testing, to confirm there is enough thermal margin (Source 2) |
Sources: 1, 2, 4, 7
This is the general case; individual cases still have to be judged on their own.
Exceptions and limits
What we saw and did not see: this article looked at one online encyclopedia entry (edited by many people), one fan maker’s selection tutorial (undated), two technical forum articles from an electronic components distributor (April 1, 2021; one with page information marked August 21, 2025), another fan maker’s technical document (version January 23, 2026), and two technical data pages from a motor maker (both undated). We did not read the full text of any standard for fan performance test methods; we did not read the definition and verification method of life (Source 1 gives only an example at 50 °C, and Source 3 does not say at what temperature life is stated); we did not read noise figures in decibels; we did not read data on liquid cooling or ionizing blowers (outside the scope of this article).
The figures are examples: 92, 120, 140 mm; 450 W, a 20 °C rise, 0.5 and 1.00 m³/min, fifty percent of airflow, a safety factor of 2; at 50 °C about 30,000 hours and over 60,000 hours; noise and the fifth power of speed; two pulses per revolution; vent area one and a half times — these are each source’s examples or statements, not selection thresholds; Sources 2, 5, 6, and 7 are maker material, each describing its own approach.
The sources do not say exactly the same thing: Source 1 says sleeve bearings may become noisy with use and are less durable at higher temperatures; Source 3 says only that bearing type has a major effect on life and noise, without explaining by type; the two do not conflict, and the main text states each separately. Source 6’s 450 W calculation is an example, and “taking operating point airflow as fifty percent of maximum airflow” is that page’s own assumption (the page says internal pressure loss is usually unknown), not a general rule.
Statements from a single source only: the 50 °C life example (Source 1); 3-wire fans’ two pulses per revolution and the locked-rotor signal (Source 2); the statements on parallel and series and the stall region (Source 5); the 450 W calculation example (Source 6); filters causing large pressure loss and finger guards almost none (Source 7); vent area at least one and a half times, and resilient mounting pads (Source 4).
Sources with a stake: Sources 3 and 4 are a distributor’s technical forum articles, and Sources 2, 5, 6, and 7 are maker material; the main text presents them all as “says,” not as general rules.
Notes on wording: Source 1 says sleeve bearing, which the main text renders as sleeve bearing, not as oil-impregnated bearing; for Source 2’s locked-rotor sensing, impeller, power budget, and sound pressure, the main text uses “locked-rotor signal,” “impeller,” “power budget,” and “sound pressure.”
The sources are in English: the Chinese version of this article is a translation.
This article’s own synthesis: the main text does not use the “this article’s synthesis” label; each statement can be traced to the sources above.
Scope: this article covers a way of thinking about selection; it does not discuss model cross-references between makers, prices, or lead times; standards for fan test methods are outside its scope.
Equipment and products: the figures and statements in “What Jiahon can help with” were read from the text of the product pages on October 13, 2026; we did not look at product images or read any specification sheet, and they were not verified by this article; specifications are as on the product pages, and for anything the product page does not state, please inquire.