I have looked into the packaging of one of these fans at HomeDepot. Its
just a 15"! (x6"?) circular shroud, and it is to be mounted anywhere- theres
no flush mounting or anything, just some metal clips. The pic in the manual
shows it mounted so it is blowing Horizontally - out of a louver vent
mounted on the front of an "attic" - above the ceiling & below the roof, at
the front of the pictured house.

I bought three 20" temperature controlled box fans ($20 each). Mounted
one over the louver vent on the front side of the garage. Mounted the
other two on the louver vents on one side of the house. The blow hot
air out, and hopefully sucks cold air into the attic from the other
sides of the house. So far it seems to work quite well. Way more
energy efficient that using the AC all the time. See my more detailed
write-up:
http://www.gearhack.com/Forums/Displ...the_Attic.html

Chieh