Raspberry pi 4 + hat case with fan

The Raspberry pi 4 has a lot more computing power than the Rpi 3, and needs much more CPU cooling. Most cases put a fan above the PCB and blow air downward. But if you have a "hat" that covers the CPU this cooling is ineffective. This case is open on the top and one side for easy access, and has provision for a 30mm fan on the side - just above the SD card. This way, air can blow between the Raspberry and the "hat". With a small (25 X 25mm), low-profile heatsink, CPU temps can be kept below 42C under most conditions.