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

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.

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.

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.

Purchased to replace fans in a Unifi USG Pro 4. The fans are the same size, still move good air and are basically silent. Full adapter, extension, and mounting hardware included was great. I used the rubber mounts and trimmed them, fans held securely. Great option for this fan size - would purchase again if needed moving forward.

Wow. I was grumpy about spending this much on fans. But I was specifically looking for something very quiet and I saw the reviews so I took a chance. I used these to replace the fans in a UniFi USG Pro 4. I had the USG installed in a bedroom and it was almost impossible to sleep with the noise. Swapping the fans out with these was trivial, and when I plugged the USG back in (before I even reassembled it) I thought I had broken it BECAUSE IT WAS SO QUIET I COULDN’T EVEN HEAR IT RUNNING. I reassembled it and it is still whisper quiet. I would GLADLY pay full price for these fans again. They’re wonderful.

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?

I thought this was really over priced for a switch fan replacement, but the quality and all the extra mounting hardware and cable connections really made my install so much easier. The fan runs quiet and also includes a resistor cable if you want to slow the fan and quiet things down even more. I will buy another for a dvr with the same size fan that has a failing fan bearing.

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.

Calidad Noctua. Para una fuente de poder ITX buscaba un ventilador con alto rendimiento y muy silencioso y Noctua es el ganador. En cuanto a presentacion desde el empaque notas la calidad premium de los materiales, la variedad de accesorios incluidos, la calidad del cable... En cuanto a rendimiento practicamente es imperceptible el ruido para la cantidad de aire que genera. Comparandolo con un Nidec no tiene nada que hacer el noctua, pero Nidec hace ruido y vibra como un mototool, aun a bajas RPM, en entornos industriales donde no importa el ruido Nidec es superior pues tiene mayor rendimiento ya que gira a mas altas RPM, Pero esque el noctua al 100% hace menos ruido que el Nidec al minimo que deja el PWM y no vibra nada, a similares RPM mueven el mismo aire, pero Noctua no se escucha nada, y nidec pues parece un mini taladro. Ni hablar, Noctua no tiene rival en relacion Rendimiento-Silencio.

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.