Noctua

Noctua NF-A4x20 FLX Computer Case Fan - Cooling Components (Computer Case, Fan, 4 cm, 3700 RPM, 5000 RPM, 4400 RPM) (Pack of 2)

Name: Noctua NF-A4x20 FLX Computer Case Fan - Cooling Components (Computer Case, Fan, 4 cm, 3700 RPM, 5000 RPM, 4400 RPM) (Pack of 2)
Brand: Noctua
SKU: B0FSCDW7FD
Price: 31.90 USD
Availability: InStock

By Mike Perry, Hardware Editor · Verified 2026-09-15

Mike Perry has researched PC hardware since 2014, tracking 80+ GPU generations, 50+ retro handheld platforms, and 30+ vintage PC configurations. He synthesises community benchmarks, manufacturer specs, and public forum data into actionable buying guides. View full credentials →

$31.90

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View Current Price on Amazon → Compare to similar cooling & fans

*Price sourced from Amazon.com. Last updated 2026-04-20. Price and availability subject to change.

Bottom line: The Noctua NF-A4x20 FLX Computer Case Fan - Cooling Components (Computer Case, Fan, 4 cm, 3700 RPM, 5000 RPM, 4400 RPM) (Pack of 2) is a specs-and-price decision rather than a crowd-consensus one in the cooling & fans category, priced around $31.90. Check the specification table above against one or two close alternatives — on price and spec fit, not on star ratings.

The Noctua NF-A4x20 FLX is a 40x40x20mm premium quiet fan sold here as a 2-pack, built for the places standard 40mm fans scream: 1U rackmount chassis, network switches, routers, NAS enclosures, and DVRs. Noctua's award-winning A-series design pairs Flow Acceleration Channels with an Advanced Acoustic Optimisation frame, so the extra 20mm of depth translates into static pressure rather than noise. The 3-pin FLX wiring gives you three speed settings via the bundled Low-Noise Adaptors: 5000 RPM when you need maximum airflow through a dense heatsink or drive cage, 4400 RPM as a middle ground…

SpecPicks Verdict

SpecPicks scored Noctua NF-A4x20 FLX Computer Case Fan - Cooling Components (Computer… using a rating × review-volume × price-fit model applied to our editorial and benchmark analysis across the cooling & fans category. Noctua's cooling & fans lineup sits within the broader category mid-tier; price and specs are the deciding factors over brand loyalty here. Judge it on the specification table and the price rather than on sentiment: check the figures that decide your use case, then put it side-by-side with two or three close alternatives in the Compare tool before clicking through.

Common buyer scenarios for cooling & fans of this kind: matching it to an existing build, replacing a failing part, or upgrading from a previous-generation equivalent. Check the spec table below against your current setup — particularly socket / form-factor / power-rating fields — and confirm compatibility on the Amazon listing before purchase. Prices, stock, and Prime eligibility update directly from Amazon's catalog and may have moved since this page was last verified.

Frequently Asked Questions

Will this fit my 1U rack server or network switch?

It fits any 40x40mm mounting pattern with at least 20mm of depth clearance. Noctua specifically targets 1U applications and fan replacements in routers, switches, NAS units, and DVRs. Measure your existing fan first: if it is 40x10mm, this thicker model will not drop in.

Is it PWM controlled?

No. This is the FLX version with a 3-pin Molex connector. Speed is set physically by the included Low-Noise Adaptors, which step it down to 4400 RPM or 3700 RPM from the 5000 RPM default. There is no motherboard-driven PWM curve.

How loud is it actually?

Noctua rates it at a maximum of 14.9 dB(A) at full 5000 RPM. Using a Low-Noise Adaptor to drop to 3700 RPM lowers it further. It is quiet for a 40mm fan, but any fan spinning at thousands of RPM is audible if the device sits on your desk.

How many fans come in the package?

Two. This listing is a 2-pack at $31.90, and each fan includes its own accessory kit: anti-vibration mounts, fan screws, extension cable, and the OmniJoin adaptor set. Note that the manufacturer's per-pack spec information applies to the pack as sold.

What if my device uses a proprietary fan connector?

That is what the bundled OmniJoin adaptor set is for. It lets you splice the Noctua onto a non-standard header found in many routers, switches, and DVRs rather than cutting the original cable blind. Check the product listing for current warranty terms.

Pros & Cons

Pros

✓ The information below is per-pack only
✓ Backed by Noctua's warranty and support channels
✓ Ships via Amazon with Prime eligibility and the standard returns policy

Cons

✗ Confirm socket / form-factor / power-rating compatibility against your build before ordering
✗ Price, stock, and Prime eligibility update from Amazon and may have changed since this page was last verified

Key Features

The information below is per-pack only
Premium quiet fan, 40x40x20 mm, 12V, 3-pin Molex, 5000/4400/370 RPM, max. 14.9 dB(A), >150,000 h MTTF
Award-winning A-series design with Flow Acceleration Channels and Advanced Acoustic Optimisation frame for superior quiet cooling performance
40x20mm size ideal for 1U applications or replacing fans in network and storage equipment (routers, switches, NAS etc.) or other devices such as DVRs
3-pin FLX version provides 5000/4400/3700rpm speed settings via Low-Noise Adaptors to fine-tune the fan for maximum airflow or near-silent operation
Includes anti-vibration mounts, fan screws, extension cable and OmniJoin adaptor set for connecting the fan to proprietary fan headers

Full Specifications

Brand	Noctua
Model	NF-A4x20 FLX
Material	Plastic, Rubber
Dimensions	40x40x20 mm
Unit Count	2.0 Count
Noise Level	14.9 Decibels
Part Number	NF-A4x20 FLX
Material Type	Plastic, Rubber
Cooling Method	forced air
Number of Packs	2
Vibration/Rumble	Yes
Compatible Devices	Desktop, Graphic Cards, Projector, Receiver, Transmission Coolers
Power Connector Type	3-Pin
Maximum Rotational Speed	5000 RPM
Item Dimensions L x W x H	1.57"L x 1.57"W x 0.79"H

Ready to buy?

Noctua NF-A4x20 FLX Computer Case Fan - Cooling Components (Computer Case, Fan, 4 cm, 3700 RPM, 5000 RPM, 4400 RPM) (Pack of 2) is available on Amazon with Prime shipping and the full Amazon returns policy. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.

View Current Price on Amazon →

*Price sourced from Amazon.com. Last updated 2026-04-20. Price and availability subject to change.