So we all want heat blur in FS right?  I had an idea and i dont know if it will work..  but what if you made a bmp so that it blured the background in fs. You can see through the smoke usualy, so there should be a way to blur it instead. I have no idea on how to start this so any help, comments on ways it will not work  (i know i'll get them)  as i said i dont know if it is possoble but i think there should be a way.

And you're applying this how? A single picture could be applied as an additional window but that would only provide a steady, unaltered "fog." It may be more feasible to make up some small pictures (.bmp) for a .gau file; this file could then be referred to under a seperate window in the panel.cfg. I'm uncertain as to 'magnification' limits for gauge files, however: this "gauge" would, basically, have to be sized in the panel.cfg to fit the entire screen.

*This gauge window would need to be prior to most all other windows (probably, that is, [Window0]).

Hagar is right.  If you want the heat blur, the most convenient way is to make it an effect, similar to "smoke".  Basically, the only difference between "smoke" and "heat" is the opaqueness/color of the effect.