Modder der8auer builds 110cm 3D-printed chimney to passively cool Ryzen 7 9800X3D without fans, cuts temps by 19C — radically simple PC mod uses the ‘stack effect’

Mechanical pressure serves as a better system to design computers around than natural buoyancy, but a new experiment from der8bauer is attempting to challenge that notion. The legendary modder recently built a chimney to exploit the “stack effect,” which uses temperature differences to catalyze natural convection to the point where it becomes effective again. As a result, the CPU in his test bench saw temperatures drop by 19 degrees Celsius without any fans.

The video above explains the concept of the stack effect pertaining to its foundation, natural convection, in great detail. Also known as the chimney effect, it relies on differences in indoor-to-outdoor air density, which are dictated by differences in temperature and humidity. The bottom of the chimney becomes a low-pressure zone, sucking in cold air that escapes through the low-pressure exit at the top.

In the experiment, der8auer uses a fog machine to show how a radiator can’t “pull” air without fans attached to it; the hot air dissipating from the other side is forced to fall back on natural convection. The test bench was water-cooled and consisted of an AMD Ryzen 7 9800X3D, so he added a temperature probe to the fittings to monitor the water temp as well. The experiment then begins with the first 3D-printed chimney that’s 10cm tall — it barely works, but temps already start to drop by 0.5 degrees.

At this point, the water was at 61°C and der8auer added another 20cm chimney atop the previous one, making the enclosure 30cm tall in total. This made the temps drop by another 5 degrees over a 30-minute stabilization period. The fog machine didn’t really show any difference in the airflow, however. Now, it was time for the big boy: an 80cm tall chimney made up of 4x 20cm parts, bringing the total height to 110cm.

Right away, temperatures began dropping below 55°C before the modder could even set up his camera for the ultrawide framing this setup warranted. Just five minutes later, the water had hit 50°C, but the visual demonstration really sealed the deal. Turning on the fog machine underneath the radiator showed air being pulled through the chimney as if there were fans facilitating airflow on top.

The CPU temperatures had peaked at 90°C previously, but the “big tower” had now brought them down to just 71°C, as reported by HWiNFO. The experiment was a raging success. The video ends with der8auer actually tying the stack effect back to how we use fans in modern PCs to synthesize air pressure, since they achieve the same goal — a pressure differential — just more reasonably. So, unless you want to redefine what a tower PC means, sticking to regular, boring old fans is enough.