What is the original meaning of Heap burning coals on their head?

To the best of my understanding, "Heaping coals upon their head" deals with the act of actually passing cinders into a basket of sorts- giving someone heat. This practice continues to this day in various parts of the world, the means of transporting may vary but the pricipal is still the same.

The importance of this may be overlooked in today's generation where we have indoor, insulated, heated HOT-TUBS and CARS let alone houses. We simply turn a dial and have fire for cooking. We adjust a knob and have warm water for tea or showers. Obviously, two thousand years ago, this ability did not exist. Fire was critical and in this context it is easy to see how 'Heaping hot coals upon your enemy's head' would be a tremendous blessing in the winter or anytime when it came to preparing food.

Of Course, the various interpretations concerning pangs of guilt, etc. still exist but this is more closely related to the physical meaning.

Given that understanding the passage makes perfect sense on the surface and also has deeper significance.