Noctua NF-A4x20 PWM, Premium Quiet Fan, 4-Pin (40x20mm, Brown)

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

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.

I recently added the Noctua NF-A4x20 PWM to my server setup, and the performance of this 40x20mm fan has left me thoroughly impressed. Noctua's reputation for premium quality is well-deserved, and this fan is no exception. Firstly, the build quality is exceptional. The brown color may be unconventional, but it's a symbol of Noctua's commitment to quality. The construction feels robust, and the attention to detail is evident. This fan exudes durability, assuring me that it can handle continuous operation in a server environment. Now, let's talk about the noise level—or rather, the lack of it. This fan is remarkably quiet, especially considering its size. Noctua's focus on providing a quiet solution without sacrificing performance is evident here. Whether my server is working at full capacity or idling, the NF-A4x20 PWM operates silently, contributing to a peaceful and distraction-free environment. The PWM functionality is a standout feature. The fan's speed is dynamically controlled based on the system's temperature needs, ensuring optimal cooling without unnecessary noise. This adaptability is a game-changer for maintaining the right balance between temperature control and acoustics. Installation was a breeze, thanks to the included accessories and clear instructions. The fan integrates seamlessly into my server setup, and the 4-pin connector allows for precise control over its operation. The performance, reliability, and quiet operation make it a top-tier choice for anyone seeking a compact, high-quality fan for their server. In my book, it's a solid 5-star product, and I wouldn't hesitate to recommend it to anyone looking to add performance and lower the noise level of their server or PC.

I bought 5 of these for cooling my 10" rack, and they work great. Easily controlled from an ESP-32 and dead silent. Mounting holes matched the drawings found on Noctua's site so they fit perfect and move plenty of air. No complaints, 10/10 would recommend.

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 makes the best fans Fan makes zero noise and quality is top notch. Premium experience opening the box, just amazing packaging. Comes with everything you need and more. Been loyal customer for over 15 years. Never had a fan go bad.

Very quiet, moves a good amount of air. Comes with many cables.

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?

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.

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.

Ticks every box and is brilliant value for money

Whisper quiet and moves a surprising amount of air for its size. You can feel the quality—definitely worth it for any small-form-factor PC build.