Why small PCs should be fanless
A PC usually relies on heat sinks and active cooling by forced airflow (ie fans) to remove heat from hot components. As the case becomes smaller so does the fan. As a fan becomes smaller it needs to rotate faster to achieve the same airflow. Faster rotation results in higher noise level and higher wearing rate. Small cases has small air vents that clog quickly and decrease airflow efficiency, which require the fan to rotate faster increasing noise, wearing and clogging rate further. This cycle cannot go forever, therefore small PCs that rely on fans for cooling are prone to overheating.
Passive Cooling and fit-PC2
Passive cooling by conduction is silent and has no moving parts that can fail, making it far more reliable than active cooling. Unfortunately it is also less efficient than active cooling. The accomplishment in fit-PC2 is bringing down the system power consumption to such a level as to make passive cooling in a small case possible.
So why is fit-PC2 case warm to the touch?
fit-PC2 case feels warm to the touch because the case itself is used for heat dissipation. What you feel is all the heat the system generates. Thermal performance is guaranteed not to change over time.