Noctua

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

Name: Noctua NF-A4x20 PWM, Premium Quiet Fan, 4-Pin (40x20mm, Brown)
Brand: Noctua
SKU: B071W93333

Bottom line: The Noctua NF-A4x20 PWM: Just 14.9 dB(A) at full 5000 RPM tilt - quiet for a 40mm fan; main trade-off: 20mm thickness will not fit slots sized for 10mm fans.

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By Mike Perry, Founder & Editor-in-Chief · Listing data updated 2026-10-18

Mike Perry — Hardware researcher since 2014, focused on GPU performance across gaming, rendering, and local-LLM inference. Synthesises community benchmarks, manufacturer specs, and public forum data into actionable buying guides. About the author →

Pros & Cons

Pros

✓ Just 14.9 dB(A) at full 5000 RPM tilt - quiet for a 40mm fan
✓ 20mm depth moves more air per RPM than standard 10mm 40mm fans
✓ 4-pin PWM gives motherboard automatic speed control
✓ OmniJoin adaptor set connects to proprietary NAS and router headers
✓ Over 150,000 hours MTTF rating

Cons

✗ 20mm thickness will not fit slots sized for 10mm fans
✗ Brown and beige color scheme clashes with most builds
✗ Needs a 4-pin PWM header for speed control to work
✗ Low-Noise Adaptor caps speed at 4400 RPM, cutting peak airflow

Manufacturer description

The Noctua NF-A4x20 PWM solves a problem most 40mm fans create: noise. At 40x40x20mm, this 12V four-pin fan spins up to 5000 RPM while topping out at just 14.9 dB(A), and Noctua's A-series design pairs Flow Acceleration Channels with an Advanced Acoustic Optimisation frame to keep airflow moving without the whine typical of small-diameter rotors. The extra 20mm depth over standard 10mm fans lets it move more air per revolution, so you can run lower RPMs for the same cooling. If you are swapping out the screaming stock fans in a 1U server, a network switch, a router, a NAS, or a DVR, this is…

SpecPicks Verdict

SpecPicks scored Noctua NF-A4x20 PWM using a rating × review-volume × price-fit model applied to published specs and reviews across the PC & gaming hardware category. Noctua's PC & gaming hardware 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 PC & gaming hardware 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 retailer's listing before purchase. Prices and stock are set by the retailer and may have moved since this page was last updated.

Frequently Asked Questions

Will this fit my 1U server?

It fits standard 40mm mounting holes, but it is 20mm thick rather than the common 10mm. Measure your clearance first - many 1U chassis and network devices only have room for a 10mm fan. Noctua makes an NF-A4x10 for those.

How loud is the NF-A4x20 PWM?

Noctua rates it at a maximum of 14.9 dB(A) at its full 5000 RPM speed. With the supplied Low-Noise Adaptor installed, it caps at 4400 RPM, which drops it further.

Do I need a 4-pin header to use it?

You need a 4-pin PWM header for automatic speed control. On a 3-pin header it will still run, just at full speed unless your device does voltage-based control. The included OmniJoin adaptor set lets you splice into proprietary headers on NAS units, routers, and switches.

What comes in the box?

The fan plus anti-vibration mounts, fan screws, an extension cable, a y-cable for running two fans off one header, and the OmniJoin adaptor set.

How long will this fan last?

Noctua rates it at over 150,000 hours MTTF. Check the product listing for current warranty terms.

Key Features

Premium quiet fan, 40x40x20 mm, 12V, 4-pin PWM, max. 5000 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 servers or replacing fans in network and storage equipment (routers, switches, NAS etc.) or other devices such as DVRs
4-pin PWM version for automatic speed control via 4-pin PWM fan headers, 5000rpm maximum speed (4400rpm with supplied Low-Noise Adaptor)
Includes anti-vibration mounts, fan screws, extension cable, y-cable and OmniJoin adaptor set for connecting the fan to proprietary fan headers

Full Specifications

Brand	Noctua
Model	NF-A4x20 PWM
Voltage	12 volts
Material	Fibre-glass reinforced PBT
Dimensions	40x40x20 mm
Unit Count	1 Count
Noise Level	14.9 db
Part Number	NF-A4x20 PWM
Material Type	Fibre-glass reinforced PBT
Cooling Method	Air
Number of Items	1
Vibration/Rumble	Yes
Air Flow Capacity	9.4 cubic meter per hour
Compatible Devices	Desktop
Power Connector Type	4-Pin
Warranty Description	6 year manufacturer’s warranty
Maximum Rotational Speed	5000 rpm
Item Dimensions L x W x H	1.57"L x 1.57"W x 0.79"H

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Noctua NF-A4x20 PWM, Premium Quiet Fan, 4-Pin (40x20mm, Brown) is listed on Amazon. Price, availability, shipping and returns are set by Amazon and its sellers — check the listing for current terms. SpecPicks earns a small commission on qualifying purchases — thank you for supporting independent review work.

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