Rys Sommefeldt

Deciso DEC3862 fan swap

Wednesday, Feb 11, 2026 · 1054 words · approx 4 mins to read

My home router is a rack-mountable Deciso 3862 and, as is common with rack mount hardware at 1U height, it’s got a reliable but noisy fan. The biggest issue isn’t the noise of the airflow, but the sound the bearing makes. It’s annoying enough when the fan is spinning at constant speed, but becomes very noticeable and irritating if the fan speed changes.

There’s not much heat for it to get rid because the main system-on-chip is a comparatively low-power embedded AMD EPYC Embedded 3000 SoC (the 8-core 3251 with a 55W TDP), so even though it’s only 40x40x25mm the fan doesn’t have to work too hard to keep the router cool here in my office.

After some back and forth with the folks at Deciso about them exposing fan control to software, so that I could get some more control of it that way, they came to the conclusion that they have no plans to do that, but did give me the specs of the OEM fan and the wiring diagram so I could think about replacing it with something else.

The OEM fan is a Sunon HA40201V4-1000U-A99 with 2-pin connector, meaning fan speed control happens via adjusting the voltage. Page 30 of the linked PDF gives us the key specs needed when thinking about a replacement: 5.5ft³ per minute maximum airflow, and 0.10 inH₂0 static pressure.

Quick aside: please take a second to marvel at the amazing non-SI unit for the static pressure. Inches of water.

Any replacement should ideally have very similar static pressure and airflow characteristics, with noise being the thing we want to adjust while keeping the rest of the fan’s operating properties the same. Deciso took care to design a custom fan shroud for the cooling system, so I didn’t want to compromise the performance of that if I could get away with it.

Thankfully Noctua have the NF-A4x20 FLX which has a very comparable static pressure of 22.16Pa and a peak airflow of 9.4m³ per hour, and a 3-pin power connector. The 3rd wire is for speed sensing, so not having it connected in this application is OK. I leave research into the weird units used in the Sunon spec sheet and how to convert to the SI units I quote for the Noctua as an exercise for you, dear reader.

The stated noise level of the Noctua is quite similar to the Sunon (in fact the Sunon is supposedly quieter), so the gamble was the the acoustics of the Noctua’s bearing are improved, and the gamble paid off.

Swapping the fan was simple. First you undo the screws keeping the black top cover to the rest of the chassis, then you slide the top cover back and up to take it off, taking care not to damage the ground wire connected to that top cover piece. That reveals the fan shroud at the back right, holding the Sunon in place:

You can see the orange Deciso logo on top of the shroud and the original Sunon fan is only held with pressure from the shroud and has no screws, which I really appreciate. That means removing it to fit a replacement is easy: just pull the Sunon out and push the replacement in, making sure the get orientation for airflow right. Air leaves out of the back of the unit, so make sure you push the new fan into the shroud respecting that:

Then it’s a simple matter of placing the shroud back where it was, locating the small clips on the shroud that hold it to the back of the chassis into their small holes.

Put the top cover back on and you’re done. There’s a warranty void sticker over one of the screws but depending on where you live consumer protection laws might allow you to disregard that.

The end result was exactly what I hoped for: the router works fine with the new fan in place and its bearing is near-silent, meaning I can’t hear the router at all now given the noise that some other things in the rack make.

Temperatures are slightly higher given I’ve also chosen to use the low-noise adapter that comes with the fan to quieten it down even further. It reduces peak airflow and static pressure, but because the EPYC 3251 gives off so little heat (Deciso offer a completely passively cooled model based on the same SoC, even) and the airflow from the fan isn’t necessary for cooling any other components on the NetBoard-A30 mainboard the DEC3862 is built from, it doesn’t cause any operational issues.

Absolute temperature is roughly 3C higher than with the Sunon, which is totally fine for my operating environment.

Hopefully this simple guide and recommendation for the Noctua NF-A4x20 FLX helps someone else out.