German modder der8auer built a massive 110cm 3D-printed chimney on a water-cooled AMD Ryzen 7 9800X3D test bench, dropping CPU temperatures by 19°C. The experiment exploits the stack effect to pull cool air through a fanless radiator without mechanical pressure.
Conventional PC building wisdom treats the chimney effect as a minor footnote, but an ambitious hardware experiment has just put the old forum theory to a rigorous test. German overclocker der8auer constructed a towering vertical duct directly over a water-cooled PC radiator to see if natural convection alone could pull enough air to cool modern silicon.
Putting the Chimney Effect to the Test with a Ryzen 7 9800X3D
The test rig relied on a custom water loop cooling an AMD Ryzen 7 9800X3D, capped at a constant 100 watts so that the thermal load entering the loop remained strictly controlled throughout the run. The 240 mm radiator operated entirely without attached fans, propped up on a bench to allow ambient air access from underneath. Left alone for an hour and twenty minutes, the water settled at 61.5°C, while a fog machine demonstrated that ambient vapor simply drifted aimlessly around the cooling fins rather than flowing through them. Under that baseline, the Ryzen chip had been peaking above 90°C.
To change the physics, the modder began bolting on interlocking 3D-printed PLA funnel segments. A modest 10 cm addition shaved off half a degree, while a 20 cm extension brought the tower height to 30 cm, dropping water temperatures by roughly five degrees over a 30-minute stabilization period. While the incremental changes proved that vertical rise mattered, they offered only a modest glimpse of what taller structures could achieve.
Scaling Up to a 110cm Tower and Chasing Down Pascals of Pressure
The real breakthrough required going vertical on an aggressive scale. The modder added an 80 cm block composed of four separate 20 cm sections, bringing the entire tower assembly to a towering 110 cm that nearly reached the ceiling. Before the camera framing could even be adjusted, water temperatures plunged below 55°C, hitting 50°C within five minutes.
When the fog machine was switched back on beneath the radiator, the visual difference was stark. Vapor was visibly sucked straight up through the ductwork, mimicking the airflow patterns typically generated by fans.
The thermal relief at the chip level matched the coolant drop. HWiNFO logs confirmed that the processor temperatures fell from over 90°C down to 71°C, marking a 19-degree improvement driven entirely by natural convection.
The Hard Math Behind Passive Cooling and Why Fans Remain King
For all the visual drama of a meter-tall plastic tower stretching upward from a desk, the experiment ultimately underscores why traditional case designs look the way they do. Calculating the static pressure generated by a standard 55 cm case with a 20°C room and a 40°C interior yields a mere 0.4 Pascal—roughly equivalent to the pressure under a layer of water four hundredths of a millimeter deep, or thinner than a human hair.
That microscopic pressure differential explains why extreme height is mandatory if you want passive convection to carry a real thermal load. While historical setups like the passively-cooled Power Mac G4 Cube and the 90-degree rotated SilverStone Raven series have played with vertical airflow dynamics before, building a practical rig requires structural compromises that few desktop users are willing to accommodate.
The fun physics make for an incredible hands-on demonstration, but the resulting funnel quickly becomes impractical. Fans ultimately achieve the exact same goal—establishing a pressure differential—without demanding a full meter of vertical clearance over your workspace.
