Is there a shader (or any other way) to get a heat effect? I mean the kind of distortion tipically caused by a very hot ground or a boiling cauldron.
thanks

You can use the perspective object (sinewave effect) and alter the offset during gameplay, or ( and probably more efficently) use one of Looki's shaders.

Thank you Adam, I've tried it but that's not quite the effect I'm looking for, since it's based on sinewaves rather than horizontal stripes with varying heights.

Could have been that specific in the first place :P

I would use a combination of the Lens effect and the Selective Background Blur effect.
Here they are, in case you don't have them:

http://www.filedropper.com/fx_1

I've got what I wanted using horizontal stripes as large as the screen and slowly bouncing up and down with the lens shader set to 0.03.
Thank you all.

Haha, alxmrg - That's exactly what I suggested to do him when he wrote me a PM
Glad you got it working.