[Kevmo]

Yes that is sufficient for me.
What would be the damage radius of such a heat outbreak?

Those islands where H-bombs were tested , they were utterly destroyed as well as ships surrounding them. That was purely from the heat, not the gamma radiation afterwards. Loooks to me about a 2-3 mile radius.

[Steely Tom]

The largest H-bomb detonated by the United States was Castle Bravo, in 1954. The crater it left in the island of Elugelab (part of the Bikini Atoll) was approximately one mile in diameter, although the surface of the island was effectively erased.

Castle Bravo was about 15 megatons.

The USSR set off a considerably bigger H-bomb in 1961; the Tsar Bomba released around 50 megatons; it was detonated about 2.5 miles above the ground and its fireball was more than five miles in diameter. It destroyed buildings 50 miles away.

It did not set the atmosphere on fire, although the shock wave it released circled the world three times.