Ditto Pat Weston's comments-
   My ES has the fan and it's typically on anytime the plane's operating but
not airborne.  When I took a demo ride in the factory ES a few years ago, it
didn't have a fan nstalled.  Though it was only in the 70's outside, it was
stifling hot in the cabin until we got airborne and started getting
sufficient cooling flow from the tail.  I believe the fan is now in the
factory plane (but I'm not sure).
   An additional option that adds significant flow on the ground is the
cabin vent air control box sold by Top Flight Service in Florida (web link
http://www.topflightservice.com/VentBox.htm ).  I first learned about this
from Jim Scales, who has one in his ES.  By moving a flapper in the box, you
allow air to recirculate in the cabin and when you're on the ground, there's
a big increase in airflow out the vents from the cabin fan.  In the winter,
when you don't want any cold air coming in the tail, you can toggle the
flapper closed and seal off the air from the NACA duct on the vertical stab.
The box has a MAC servo on it to move the flapper.  It's not cheap (around
$450 as I recall), but appears to be very well made.  To save myself some
money, I fabricated a box of this design out of fiberglass.  It took an
inordinate amount of time, but it works fine.  If I had it to do over again,
I'd buy the box.
   Hope this helps,
   Skip Slater
   N540ES