Burner efficiency of a hot air balloon decreases approximately what percent for each 1,000 feet above MSL?

• A. 4 percent
• B. 2 percent
• C. 6 percent
• D. 8 percent

Answer: (A)

As you climb, air gets thinner, and that directly affects how well the burner can heat the envelope air. With less dense air and lower ambient pressure, the flame mixes with fewer molecules and heat transfer from the flame to the balloon air becomes less efficient. In practical terms, for the same amount of propane energy, you don’t achieve as big a temperature rise in the envelope, so burner efficiency drops. Pilots use a handy rule of thumb: about a 4 percent decrease in burner efficiency for each 1,000 feet above mean sea level. This helps estimate how much extra burner time or propane you’ll need at higher altitudes. Keep in mind the exact value can vary with burner design and conditions, but 4% per 1,000 ft is a commonly cited estimate.