At first, follow your user manual, where to place your box.
For those, who doesn’t want to use for any reason third party plugin Fancontrol2, I suggest to set
Menu > Plugins > Manual Fan control to “ON” in standby. (I personally prefer Deep Standby which keeps box cooler, or total power off when no recordings are programmed.)
Menu > Plugins > Manual Fan control
Fancontrol2 is a better solution, because you can control speed of your box fan.
Press Green > Yellow > Addons Download Manager > BH Addons Plugin > Fancontrol2
After installation and reboot is possible to configure Fancontrol2 (blue > press long or Menu > Plugins > FanControl2)
4Pin configuration is the best I found for my Solo2.
Try the best for your use and please, report your experiences and tests on other boxes (Fan type).
You can also check your fan by LAN/WLAN typing in browser http://IP of your box/fancontrol