I made the base text and duplicated it, blurred it, did 'Wind' and then did 'Ripple'. Duplicated this layer and blurred, then set the layer mode to dissolve lowering the opacity.
Used the 'Render'> Nature> Flame. Made a nice flame using red and yellow. Flipped, rotated and scaled the flame render for each number and placed it behind everything.

I was making a tut, but only got about 1/4 the way through and my Gimp crashed (auto save not enabled). I only managed to get 4 screenshots of how I did the base text, but wasn't able to get to the making of the flames.