[joseflavio]

I have 3 fanless desktops and you can build them quite cheaply if 65w cpus are enough for you. You can get a fanless seasonic power supply for 90 usd and use cpu cooler Artic Alpine 12 for 25 USD - the remaining components including the case can be quite standard

[maxmalkav]

The "problem" of using a regular case for totally fanless setup is these cases are designed with a fan-generated air flow in mind. The cases designed for passive operation, like the DB4 try to generate some airflow by convection to compensate.

A setup like the one you describe can be quite OK (specially with modern hardware), but it may run kind of warm-ish due the lack of proper airflow (and heat kind of shortens life of electronic components in the long run). Worst case scenario, you can always install very low RPM fans to this setup.