The Raspberry Pi Foundation released an official Raspberry Pi 4 Desktop Kit. The kit comes with a new plastic case featuring holes for every port on the Pi 4, but nothing at all for ventilation. This project uses the official Raspberry Pi 4 case, though you can use any other case to accomplish this project as well.
Most Raspberry Pi models don't need fans or heatsinks for everyday use—but the Pi 4 is another story. The CPU idles around 60°C. Running heavy processes can heat the board so much it hurts to touch. Too much heat will cause the CPU to throttle, causing serious performance issues.
Jeff revealed some telling images by photographing the Pi 4 with a thermal imager. Most of the heat appears to come from the USB-C power circuitry. Since the heat has nowhere to leave inside the Pi 4 case, he decided to install a fan. Here's a quick breakdown of the project.