Der8auer cools CPU with tall 3D printed tower

For over 25 years, tech enthusiasts have relied on trusted sources for analysis and advice. A long-standing piece of PC building advice is the chimney effect, which claims that a case works like a flue, and that pointing top fans outward gives hot air a natural boost on the way up.

German overclocker der8auer decided to test this claim by building a custom setup. To do this, he needed to understand how a chimney actually works, which isn’t quite what forum posts assume. A chimney works because rising air is trapped inside a tall channel, so as it climbs it drags cool air in behind it through the bottom.

A normal case doesn’t have much height to work with. der8auer ran the math on a case 55 cm tall, assuming a 20°C room and a 40°C interior, and landed on 0.4 Pascal. He compares that to the pressure you’d feel under a layer of water four hundredths of a millimeter deep – thinner than a human hair.

Since that’s functionally nothing, he went hunting for height. His test rig ran a custom water loop around a Ryzen 7 9800X3D, capped at a constant 100 watts so the heat entering the loop stayed the same throughout.

The 240 mm radiator had no fans attached and sat propped up off the bench so air could reach it from below. After an hour and twenty minutes, the water settled at 61.5°C, and fog blown underneath drifted around the fins instead of through them. der8auer began stacking 3D-printed PLA shrouds onto the radiator.

The first was only 10 cm and still shaved off half a degree, which he admits he didn’t expect. A 20 cm section brought the tower to 30 cm total, and between the two the loop gave up around five degrees over the next half hour while the room temperature never moved.

Then came the big one: an 80 cm block of four sections that brought the whole assembly to 110 cm and nearly reached his ceiling. Water temps fell below 55°C before he’d finished bolting it together, hitting 50°C within five minutes.

Those water numbers matter for what they do to the chip underneath. The Ryzen had been peaking above 90°C with the radiator bare; HWiNFO put it at 71°C once the tower was standing, a swing of nearly 19 degrees with no fan moving air anywhere.

Der8auer’s test shows that the chimney effect can be used to cool a PC, but it requires a significant amount of height. While this method can be effective, it’s not practical for most users. Fans are still the sensible option, as der8auer himself concludes, as they chase the same pressure difference without demanding a full meter of vertical clearance above your desk.

In practice, this development means that people looking to cool their PCs may need to consider the height of their setup. For those with limited space, traditional cooling methods may still be the best option.

However, for those with more space available, exploring alternative cooling methods like the chimney effect could lead to significant temperature reductions. They may also consider other methods, such as using a custom water loop, which der8auer has experience with, having previously converted a $7,000 RTX 5090 Lightning Z to custom water cooling.

His experience with custom cooling solutions is evident in this test, and his findings provide valuable insights for those looking to optimize their PC’s cooling performance.