First draw the fan, then from the fan location, click and drag the fan (line tool) in the direction you wish it to blow. This won't draw, just set the direction.

@arlo
Read. The. FAQ.

@arlo Press Shift while drawing where you want your fan to go this will make the fan move that way And you should lock this thread

Macquarry

@MacEmo (View Post)
Requesting a lock when it is not your thread is a 2 hour banable offence.

@arlo If you really can't do it, I will specify.
now,
1) select fan.
2) Make the brush size large
3) Drag a line of fan using shift+hold click
4) once you have your fan, click on the original starting point of the fan (Where you drew it from)
5) shift+hold click and drag in the direction you want the fan to... blow air to and make it as long as you want it strong
6) observe how it now blows particles in that direction

Once you understand how it works, you can take shortcuts.