Review on UpHere U1203 Silent Dual 120mm USB Fan - Optimized for Computer Cases, Cabinets, PlayStation, Xbox Cooling by Gerald Hill

Fans don't move much air, but they're quiet and run off the Roku's USB source and WiFi router. Airflow is weak, but meets the need to keep the device's temperature low so it's inaudible. Not worth getting speed control, the difference in airflow and noise level is negligible and really not worth the cost and probably adds a point of failure.