Noctua NF-A4x20 PWM, High-Performance Quiet Fan 40mm

I purchased the Noctua NF-A4x20 PWM for use around my home server/networking equipment, where I needed additional airflow in a space that simply couldn't accommodate a normal 80mm or 120mm fan. For such a small 40mm fan, I'm impressed with it. I've dealt with small fans before, and one of my biggest complaints is usually noise. Small high-RPM fans can produce an annoying high-pitched sound that is much more noticeable than the noise from larger case fans. This Noctua is considerably more refined. The 20mm thickness was also important to me. There are plenty of 40mm fans available, but when you're trying to move air through or around equipment rather than simply circulate air in an open case, having a little more substantial fan is useful. I specifically purchased the PWM version because I wanted speed control rather than having the fan run at full speed all the time. In a home server environment that's a big advantage. I can provide more airflow when equipment needs it while keeping unnecessary noise down during normal operation. Build quality is excellent. The fan, cable and connectors all feel like quality components, and Noctua includes a surprisingly useful assortment of accessories for such a small fan. It's certainly possible to buy cheaper 40mm fans, but I've learned that saving a few dollars isn't always worthwhile when the fan is going into equipment I expect to operate continuously. That's particularly important for me because much of my server and networking equipment runs 24/7. A cooling fan isn't something I want to replace regularly or constantly wonder whether it's still spinning. Don't expect a 40mm fan to move air like a full-size PC case fan—that isn't what it's designed to do. The advantage is being able to provide directed airflow in places where a larger fan simply isn't practical. It's more expensive than many generic 40mm fans, but after using it, I understand what I'm paying for. It's quiet for its size, PWM controllable, well built, and feels designed for long-term use. For a server, network enclosure, electronics project, or other application requiring a quality 40mm PWM fan, I'd happily buy another one.

The Noctua NF-A4x20 PWM is one of those tiny components that punches hilariously above its weight. At 40mm, it looks like it should be decorative, yet it’s capable of transforming loud, grumpy network gear into something that no longer sounds like it’s preparing for takeoff. Drop one of these into a firewall or switch that shipped with a fan clearly designed by someone who hates silence, and suddenly the room feels calmer, cooler, and more civilized. It’s small, precise engineering doing a big favor for your ears. In real-world use, this fan is a peace offering to anyone who’s had to live near enterprise hardware. It moves air efficiently for its size, ramps smoothly under PWM control, and avoids that high-pitched whine that cheaper 40mm fans love to produce. Thermals stay under control, airflow is steady, and the fan itself behaves like it understands its job description. It doesn’t try to impress; it just quietly fixes a problem you’ve been ignoring because you assumed loud was unavoidable. Where the NF-A4x20 really shines is in reclaiming sanity from gear that was never designed for human proximity. Firewalls, routers, compact servers—anything that technically fits under a desk but audibly objects to the arrangement—benefits immediately. It’s the kind of upgrade that makes you wonder why manufacturers insist on shipping jet-engine fans in devices meant to live in offices. The improvement isn’t subtle; it’s the difference between “background noise” and “oh, I forgot that thing was on.” Noctua’s usual attention to detail is all here: solid bearings, predictable PWM behavior, and build quality that inspires confidence. It’s not flashy, it’s not exciting, and it doesn’t need to be. It simply does what good engineering is supposed to do—solve a problem cleanly, quietly, and without introducing new ones. Pros • Dramatically quieter than stock 40mm fans • Smooth, predictable PWM control • Excellent airflow for its size • High-quality bearings and long service life • Instantly improves livability of noisy network gear Cons • 40mm size still limits absolute airflow • Requires compatible PWM control • Physical fit can vary by device • Once installed, you’ll notice how bad the original fan really was

Got these to install in a MikroTik switch that is inside my office area. Worked great! They fit pefectly and the fan header connectors were compatable with the switch. They would probably also work in a 1U server but they may not push enough air for really demanding cooling. Switch and router and lower power 1U devices they are perfect. Also include the standard Noctua goodies in the box. Very nicely made and high quality.

Super quiet. High quality with many included accessories, the 2 pin conversion connector saved me a lot of time. Ugly, butt they're the best

My network NICs run hot and need active cooling. I initially used some cannabilized small 40mm fans but the noise profile and the noise level itself was not pleasant, especially for a home office server. I switched to these and they are noticeably quieter while maintaining a higher degree of cooling. The color is a little ugly as always but it’s buried in a metal box and never looked at anyway.

I used these to replace the 3 extremely loud fans in a Terramaster D4-320U. WIth the stock fans, I could hear the device in the adjacent room, even though the closet room where the rack was located was closed off. This was an easy installation, unscrew, unplug and remove the 3 stock fans, screw in and plug in the new fans. Completely silent, with good, acceptable airflow.

It's quiet, which I like, and it comes with super thoughtful accessories. Those things are carrying the weight of my 4 stars, because the big issue is that the fan doesn't move much air. Not nearly as much as a typical "thick" 40mm fan. I just don't know what the application is. If you try to replace a screaming server style fan, these will not come close to moving enough air. Maybe this is good if you have space and want to replace a loud 40x10 fan?

Very good quiet fan. Works as intended to cool the hot PC Chipset.

Noctua es símbolo de calidad aunque un poco caro son sus productos. Para Canarias no recomiendo los envíos premium ya que tardan lo mismo que los normales.

Adding adding 10G copper transceivers, the stock fans were unbearably whiny because the copper transceivers run crazy hot. I swapped the stock fans to these and now all I get is peace and tranquility.

Got 3 of these in my 1U server and it’s very quite, compared to my old fans.

Ich habe diese Lüfter gekauft um den Geräuschpegel diverser Netzwerkgeräte in meinem Serverschrank zu reduzieren. Die Installation ist einfach und man hat so einiges an Zubehör dabei. Die Lüfter sind ausserordentlich Leise und fast nicht zu hören. Die Kühlleistung ist akzeptabel, aber natürlich nicht vergleichbar mit echten Server-Lüftern. Für wen aber ein paar Grad mehr in den Geräten im Gegenzug zu deutlich leiseren Lüftern akzeptabel ist, sind diese hier sehr zu empfehlen.

高回転で静か、風量も十分あるチップセット冷却に使ってます。