Hideous Destructor has something like this, and it could make thermal weapons more interesting.
Would apply to things like the incendiary grenades, and the plasma weapons
Could be applied as an area effect to other nearby actors
Don't "build up" heat indefinitely, though. Things should only be able to get as hot as the fire that heats them up, unless they can, themselves, properly ignite and burn
Hideous Destructor has something like this, and it could make thermal weapons more interesting.