No smoke

What is smoke? It contains soot. (We will come back to this later) It also contains incompletely combusted material.

And that means that smoke is actually a source of fuel. Which is why houses in the past used to catch fire. The fire place heated up the smoke but was not hot enough to get it heat so the smoke escaped out of the chimney. 

I will let you figure out what happened out.

That was why there was an ancient vocation called chimney sweep. If you did not clean the chimney, the build up soot could catch fire.