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Sliger S620 meets again the D15S : the King is dead, long live the King ! (06th January 2026)
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While building a setup inside the Sliger S620, there is clearly an elephant in the room : to use the Noctua D15 CPU cooler. After all this case was designed mainly for this massive heatsink.
As not so obvious as it can be, my first experience using the D15S within the S620 was not totally positive. Back to 2021, I used an AM4 (PGA) setup (Asus B450i) and I was not impressed, especially due to the bad acoustics (rear intake generated massive vibrations & parasite noise) & it was very cumbersome. However the D15S proved to be pretty effective at CPU cooling.
https://smallformfactor.net/forum/threads/sliger-s620-itx-master-piece.16505/
The Noctua D15S
As I wanted to push the limits on this build, I decided to try again the Noctua D15S CPU Cooler inside the Sliger S620.
Please keep in mind that the D15S is an alternative version of the D15 with an asymmetrical heatsink and only 1 fan (NF-A15).
This time, several elements are helping it :
- AM5 socket, using LGA. This is a critical point, as in the S620, we often remove the CPU heatsink for maintenance (GPU removal, SSD removal). With a LGA socket, where the CPU is firmly secured, it is WAY easier compared to a PGA socket ((AM4) where the CPU has almost 100% chance to come with the heatsink.
- AM5 negative offset (-7mm) mounting bars. This is helping the proper position of the heatsink within the S620, leaving good clearance with either the GPU and the top of the case!
- My better experience on cooling components without generating tons of parasite noise…

Here is the final setup :
AM5 Offset mounting bars
No rear intake fan, just one fan on the D15S setup as push (intake from rear). Please note the comfortable clearance between the CPU cooler heatsink and the RTX 5090 FE
One side exhaust fan (Noctua NFA12x25 Chromax)
Overall the installation / removal of the D15S is simple inside the S620 with this combination.
But what about the performance?
I was expecting an important CPU cooling improvement but GPU/SSD downgrade…I was wrong…totally wrong even.
Here is the benchmark, using the torture test on the Speedway, to simulate combo CPU-GPU use. The RTX 5090 FE is at stock settings (575W TDP)
As a summary of the comparison between the Cerberus-X and the S620 :
- RTX 5090 FE Core temperature : -3°C (71°C vs 74°C)
- R7 9800X3D temperature : -13°C (68°C vs 81°C)
- SSDs : no difference (~50°C)
- Chipset : as a side note, the Chipset/VRM fan speed was noticeably reduced versus the IS-67-XT setup (from 4000 rpm to 2000rpm)
As simple as it is, the S620 has just beaten my Cerberus-X. I would assume that the RTX 5090 FE thermals were on par with fewer fans (I was unable to replicate those GPU temperatures whereas I managed to do it on the CPU), but the R7 9800X3D is noticeably improved, thanks to the rear intake of fresh air on the S620, that the Cerberus-X is lacking (ATX motherboard is creating a bigger gap from the rear panel, and no side exhaust while using tower cpu cooler).
The D15S is also improving the temperature of the other components (SSDs, VRM, Chipset) versus the IS-67-XT.
The King is dead, long live the King!
The Noctua NF-A14x25r G2 fan
As an addition, I tried the new Noctua NF-A14x25r G2 fan, especially as it is existing in black version now.
Here is a direct comparison NF-A15 (Gen 1) vs the NF-A14x25r G2
Replacing the fan inside my setup was rather simple. I even took the opportunity to dissamble/assemble (without repasting) the heatsink to check for the top ssd.
I’ve redone my thermal test and I discovered another point : to get proper rear intake of fresh air, the 14cm fan has to spin at around 1000rpm.
In fact I tried the NF-A14G2 at 900rpm and 1050rpm.
At 900rpm, the R7 9800X3D took 5°C above the NF-A15 (1000rpm)
At 1050rpm, the R7 9800X3D temperature was the same as the NF-A15 (1000rpm)
Overall, I consider the Noctua NF-A14x25r G2 as an improvement, not really by its pure thermal performance but by its ratio noise/performance that is outperforming the NF-A15.
With the NF-A15 I was limiting its speed to 1000rpm to limit its noise (mostly a specific “hum” noise that is clearly audible & disturbing). The NF-A14x25r G2 is allowing higher speed (higher performance) as it can reach higher speed with less noise.
Since I got the R7 9800X3D, taming its heat was an issue. I clearly hate when it is reaching its thermal limit of 95°C, like on most SFF build. By moving to the S620 I’m able to fit the D15S and definitely tame the R7 9800X3D, while achieving best in class thermals & noise!
Clearly my target to beat the Cerberus-X is achieved and I’m a little bit surprised after all.
To finish, here is the final setup :
- Case : Sliger S620, desktop-horizontal orientation
- Motherboard : ASUS ROG STRIX X870-I GAMING WIFI
- CPU : AMD R7 9800X3D (CO -14)
- RAM : Corsair Vengeance 2x24Go DDR5 7600 MTS CL36 (DOCP I profile)
- CPU Cooler : Noctua D15S Chromax + Offset -7mm (NM-AMB12) with reverse flow (intake from the rear). Only push orientation to avoid turbulences
- PSU : Corsair SF1000 with stock cables
- RTX 5090 FE : Undervolted
Core Curve : 825-910 : 2700 MHz
GDDR7 +3000
Power limit : 100%
- SSD #1 : Samsung 9100 Pro 2To (Slot 1 gen5)
- SSD #2 : WD SN850X 2To (Slot 2 gen4)
- SSD #3 : Samsung 990 Pro 4To Through USB4 port
- Bottom Fans : 2xFractal Design HP-12 (intake ~1000rpm)
- Side Fans : 1xNoctua NFA12x25 Chromax (Exhaust ~1400rpm)
- Custom fan curve : Yes ("Fan control" Software)
More to come, stay tuned!