Liquid propane is used to heat hot air balloons. Propane is a stable and predictable fuel although it is also extremely flammable. It is carried in liquid form, under pressure, in 10 to 20 gallon stainless steel fuel tanks and supplied to the burner through flexible hoses. The burner flame will shoot up approximately 10 to 15 feet in a blast that is controlled by the pilot. The typical 90 minute flight will use about 20 gallons of propane.
Many balloons have redundant fuel and burner systems for added safety.
Flights in hot air balloons have been recorded at over 50,000 feet above sea level. However, the sport of ballooning is most enjoyable at altitudes of 200 to 500 feet - just above the tree tops. When balloons fly over populated areas, they usually maintain an altitude of at least 1,000 above the surface unless they have special clearance from the FAA to fly lower. Most hot air balloons can fly for 2 to 3 hours depending on outside temperature, altitude and weight carried. On cold winter days flights of 3 to 5 hours are possible.