Well, hot air balloons are pumped full of thousands of cubic feet of hot air, which gives them their lift. You see, air expands when heated. When a balloon rises, it's because the air inside the bag is warmer and lighter than the air on the outside of the bag. In order to go anywhere, a balloonist needs a stable, safe heat source to keep pumping warm air into the bag. A propane burner, which causes that loud roar you hear when a balloon is overhead, does the trick nicely.
Propane is a relatively safe gas that makes a flame that can reach up into the bag.
Of course, the balloonist's travel route is pretty much dictated by wind direction. But with the burner, they can control altitude by how much hot air they pump into the bag. Balloons are also equipped with rip panels or parachute tops, which slowly empty the balloon of air when it's time to make a descent. Thursday In the early days of hot-air ballooning, the aeronaut had to fill the bag with hot air on the ground, or he needed to carry dangerous open fires aloft. As you might imagine, accidents were frequent.