This movie shows how to make better heat haze using FumeFX. When we render somke element, it can be used for displacement map for heat haze. But using RGB gradient for smoke color, we can get nicer result. RGB color has an enough contrast so we can get finer detail from it. Gradient color moves along to fluid motion so we can see it as an air flow.
It's little bit hard to see clear differences in this movie because of video compression, I prepare jpeg sequence. You can DL here.
Gradient AGT file is here.