Hot air balloons are the first aircraft flown by humans. The first flight was made in Paris, France in 1783.  The inventors of the balloon are Joseph and Etienne Montgolfier.

They work by simply raising the temperature of the air contained in a fabric bag above the surrounding air. An open flame on a platform was how the first balloons were heated.  The first aeronauts did not realize it was the heat and not the smoke which provided their lift.  However, the smoke sealed the holes in their fabric allowing the hot air to be trapped.

As the sport evolved so did the technology. Modern hot air balloons are flown using propane to fuel the burner.

Piloting a balloon requires a pilot license rated for lighter-than-air which may include the limitation of on-board heater.