I converted the mud room to a miner room. We use some of the high-velocity metal blade fans you mention, but also stuck one of these in the window that the miners exhaust towards:
http://www.canarm.com/HVAC/Wall_Mounted_Shutter_Fans/XFS_Series_Exhaust_Shutter_Fan
XFS Series Exhaust Shutter Fan
- Smooth, quiet, reliable, maintenance free operation.
- Available in 12” to 24” sizes.
- 12” and 16” models are 3 speed
- 20” and 24” models are 2 speed.
- Durable steel construction with powder coat black finish.
- Swept back, high efficiency, low noise blade design.
- Quiet, aluminum shutters with tie bar to maximize airflow.
- Strong powder coated OSHA guarding inside.
- ETL certified
- Euro design outside rotor motor for higher efficiency.
- Totally enclosed with sealed ball bearings
- Pull chain speed control
- 9 foot cord with 115 volt, 3-prong plug
- Fans shipped totally assembled.