[MotorBikeLes]

Andy and Julie, I also forgot to mention that hot air has higher viscosity than cold, so the gain is likely to be greater than simple gas law prediction. Now of course if it were a positive displacement pump, not a simple fan, the only gas laws would apply.
The resistance of a simple "hole in wood" is much greater than a simple orifice in sheet.
For practical purposes, the resistance is inversely proportional to the area for a simple orifice, but gets more complicated with a "length", where the surface roughness has an effect, and strange "rules" come into play. A full understanding is way beyond me, I just know enough to know I don't know.
Les.