Even Cyberpunk 2077 Pushes It Too Far for Fanless PCs

Billet Labs, a London PC cooling specialist, has published stress-test results for a fully fanless system built around an RTX 5080 and Ryzen 7 9800X3D. The machine uses a passive water-cooling setup with three radiators and copper tubing, then relies on natural convection to dump heat. Tested in Cinebench, FurMark, and Cyberpunk 2077, the build proved that high-end fanless cooling is technically possible, but the numbers also make its limits hard to ignore.

The rest of the hardware is equally serious: a Gigabyte AORUS Pro B850 motherboard, 32GB of memory, a 2TB drive, and a 600W Flex ATX power supply. Billet Labs did not chase a tiny footprint here. Instead, it spread thermal load across stacked radiators measuring 120×240mm, 140×280mm, and 200×400mm, mounted above the core components. The motherboard sits on an 8mm-thick aluminum plate, with thick thermal pads transferring motherboard heat into that plate, while thermal paste under the power supply helps dump PSU heat into the same structure. In effect, the whole chassis is being used like one giant heatsink.

At idle, the setup behaves normally, with coolant temperature holding at around 28°C. Under Cinebench, though, the Ryzen 7 9800X3D pulls more than 130W. After roughly half an hour, coolant temperature rises to about 39°C, while average CPU core temperature gets close to 90°C. That is not a minor warning sign. It suggests the cooling system is already near its practical ceiling, and that a fanless approach is simply a poor fit for sustained full-load operation on a CPU in this class.

The GPU result is more impressive, at least at first. In FurMark, coolant temperature climbs to around 53°C. In Cyberpunk 2077, it goes higher still, reaching about 55.5°C. The RTX 5080 does not throttle during the GPU-heavy test, which shows this passive design can handle a flagship graphics card for a while without immediately falling apart under load. But "can handle" is not the same as "can sustain." When Cinebench and FurMark are run at the same time, coolant temperature eventually hits 60°C, and the CPU begins to throttle. At that point, the bottleneck is obvious: not the graphics card first, but the system's overall thermal capacity and cooling headroom.

Viewed as a product, this feels more like a showcase prototype, or an industry-facing demo unit, than a daily-use PC for ordinary buyers. It successfully proves that passive cooling is not fantasy and not something that is "completely impossible" to build. It also makes the tradeoff very plain: you can buy absolute silence with sheer thermal mass, but the performance margin disappears quickly, especially once a high-end CPU and a flagship GPU are pushed together.

For most people interested in a fanless PC, the better fit remains light office work, living-room media use, a download box, or a low-power workstation that is not being pushed hard. If you expect a gaming rig or a full-performance productivity machine, the gap between expectation and reality will be large. This system can run that class of hardware. It just shows, very clearly, how quickly temperature, power draw, and performance start pulling against each other once you do.