I was lucky that a 20″ box fan fits perfectly into the attic access on my house. I plugged it into one of these in the nearby hall light::

http://www.google.com/products/catalog?q=lamp+socket+outlet+adapter&hl=en&rlz=1C2CHFA_enUS484US484&prmd=imvns&bav=on.2,or.r_gc.r_pw.r_qf.&biw=1050&bih=610&um=1&ie=UTF-8&tbm=shop&cid=8680316333566283154&sa=X&ei=KBMvUPLdGoKNrgG794DIBg&ved=0CGoQ8wIwAQ

and I have a cheap whole house fan. I’m sure it’s not as good as the real thing, but it sure does help get the house cooled down in the evening.