I normally fly with the recirc fan off - just because I prefer not to hear the airflow sound.

Would the recirc fan being off affect any aircraft systems such as cockpit temperature, co-pilot window fogging/icing, pressurization?

 

BR,

Mike

AFAIK the recirc fans are not on the MEL so you can fly without them. However, bleed air on the Q400 is pretty weak so without the recirc fans the cabin can get stuffy with pockets of stale air, so you almost always have recirc fans on. IIRC air direct from bleeds/packs is discharged through ceiling and floor level grills, so without recirc fans the nozzles above passengers heads do nothing! Further details over at http://www.airliners.net/forum/viewtopic.php?t=733695#p10592395

TBH I'm surprised you can hear the recirc fans in flight, the avionics fans (which are much louder in the cockpit) and wind rushing tend to drown them out.