Which direction should I install my Hyper 212 Evo?

Mount it as the Hyper 212 Plus see image 6
with the fan blowing to the rear exhaust
http://www.coolermaster.com/product.php?product_id=6603

Here's a fantastic guide with pictures on how to install a CM 212+. Its should be nearly identical to the EVO. There's even comments regarding orientation (horizontal vs vertical) that may answer your own question. Airflow does run front to back, but all depends on how your Chassy fans are set up.

http://www.tomshardware.com/forum/258023-29-installing-...

Good Luck

Push air out the back of the case. I put a thin line of thermal paste on each of the copper pipes, seems to be working well. Temps are 35/37 c idle and 60/61 prime95. Just make sure the hold down bracket is oriented correctly. Its very tricky look at the included instructions. The "elbows" should be pointing out not towards each other and theres a little nook for the bracket to catch.