Making a Rotating Fan

First Entity to use is the prop_static and go to the World Model parameter and
browse for the fan housing model.(models/props/de_prodigy/fan_housing.mdl)
No need to adjust any settings. You can adjust the pitch yaw and roll settings
to rotate fan housing if needed.
In my example I have the fanhousing model pitch yaw roll setting at 90 0 180.
Just so it sits in my wall properly.
Place it where you want the fan to be,then align it to your walls or build your walls
around it.

The next entity will be the prop_dynamic, go to the World Model parameter and select the
fan model. If you adjusted your fan housing model setting do the same for the fan model.
In my example I would change the pitch yaw and roll setting 90 0 180.
There are alot of other settings you can do if you needed to, but the only thing you will
need to do is parent the model to the func_rotating brush that we are about to make.

So let's make that func_rotating brush entity. Make a brush covered in the origin texture and
place it in the center of the fan model. Hit the "To Entity" button on right side of Hammer Editor
and make the brush a func_rotating entity. Name it (mine is named fanspin).
In the properties window you can select the max rotation speed, the rotating sound you want
the fan to make. Then click on the Flags tab and select Start On and if you rotated your fan
housing and fan model you would click the proper axis for the func_rotating brush to turn on.
My example has the x-axis checked off, also you can check the other selections if needed.
Don't forget to Parent the fan model to this func_rotating brush.

That should be it.