How to achieve heat waves

How would I create heat waves. Like you look at a hot road and you can see the rays of heat coming off the road or alot of times you will see a fire or the Sun being shown with heat coming off of it.

 

Not quite sure what you mean by rays, but if you're talking about heat haze, you could render the scene normally in one pass, then have a particle system that comes off the object (still using the previous scene's z-buffer) in another pass and use that as a turbulence map in a post process.

 

Given you use Unity Pro (otherwise you won't be able to do it, as refraction requires rendertextures), you can check out "Forest talks particles" video from Unite 2007 ( http://unity3d.com/support/resources/unite-presentations/forest-talks-particles ) which shows you a very cool and non-repeating way of doing it

 

Yes this worked dream. Thank you. I had already done something similar to this by putting a layer of refraction over water, but using this in conjunction with it definitely added what i was looking for.