The stack effect — also known as the chimney effect — is the basic principle that hot air not only rises, but if guided through a tube, the rising hot air will create more pressure that will effectively draw air more effectively into the tube. This is not only great for a chimney, but also a useful principle if you seek to cool something like a PC in a more passive manner. The main question is of course how much of a ‘chimney’ you need to see real effects for something like a typical water-cooled CPU’s radiator, as demonstrated by [der8auer] in a recent video.

Although there’s a lot of fun physics behind the stack effect that you can run the numbers on, the more practical demonstration here using 3D printed funnel segments for the radiator and various thermometers provides a very hands-on feeling for what you can expect from this approach.

With just a single segment stacked there is already a clearly noticeable temperature change, with the second segment creating a draft as visualized by the smoke machine. After this he goes for broke with the full stack and a resulting 19°C temperature drop on the CPU. While impressive, at this point the required funnel gets a bit silly, though the same principle has been applied to computer cases before, including the passively-cooled Power Mac G4 Cube and the 90-degrees-rotated SilverStone Raven series of cases, like the RV02.

The basic idea of making use of the fact that hot air rises, and maybe also banking on the stack effect for some free passive cooling, clearly isn’t so crazy.