Why small PCs should be fanless
Typically, a PC relies on heat sinks and active cooling by forced airflow (i.e., fans) to remove heat from hot components. As the case shrinks so does the fan size. A smaller fan needs to rotate faster to achieve the same airflow. Faster rotation results in a higher noise level and a higher wearing rate. Small cases have correspondingly small air vents that clog quickly and decrease airflow efficiency, requiring the fan to rotate even faster increasing noise, wear and the clogging rate further. This cycle cannot continue forever, therefore small PC's relying on fans for cooling are prone to overheating.
Passive Cooling and fit-PC2
Passive cooling by conduction is silent and avoids moving parts that can fail, making it far more reliable than active cooling. Unfortunately it is also less efficient than active cooling. fit-PC2's system power consumption is low enough to accomplish passive cooling in a small case.
So why is fit-PC2 case warm to the touch?
fit-PC2's exterior feels warm because the case itself provides heat dissipation. You feel all the heat the system generates. Thermal performance is guaranteed to remain constant.