A hot air balloon can fly because the heated air inside the balloon is lighter than the colder air around it. The more dense and cold air beneath the balloon apparatus pushes it upwards into the air. The construction of a hot air balloon consists of a large balloon envelope, a burner that requires propane fuel from a tank, parachute valve and a basket.
For flight, propane fuel from the tank must flow into the burner to heat up the air in the balloon envelope. The balloon envelope begins to expand and rise with this hot air, which also causes the basket with the pilot to be lifted up from the ground. The valve on the tank is used to control how fast the balloon rises. To make the balloon move downwards, the parachute valve, or vent, which is at the top of the balloon, is opened to let hot air escape.
To make the balloon move horizontally or sideways, the pilot moves the balloon either up or down to catch air currents that will steer the balloon in the direction he wants to go.