Different fuels absolutely burn at different temps.

I'm a welder and a blacksmith.

When you're using coal, you use an easily ignitable fuel, like wood or naptha to get the coal to burn.

The coal burns hotter and is harder i start than your starter fuel, and cannot be started with just a spark.

The coal burns down into coke, a totally different substance, which burns hotter than the coal.

Even still, on your third level of fuel, in order to actually get steel to a workable temp, you've got to add more oxygen, to make it burn even faster and hotter.

This is all inside a forge, a device that's well insulated and made to heat steel to a workable temp.

There are other fuels that can be made to work, and they all also require blower fans, to add more oxygen.

Or in the case of an oxy/acetelne cutting torch, a bottle of pure o2

Charcoal, derived from wood in a similar fashion to coke from coal, can sort of be used, but does not and will not burn hot enough for anything much larger than a spoon, and aimply can't get hot enough for forge welding.

Now, essentially a giant housefire, getting hot enough to get those steel beams to fail? Sure!

Why'd they collapse from the bottom, that wasn't on fire?