What happens to burner efficiency as you gain altitude, per 1,000 feet?

• A. It decreases by about four percent per 1,000 feet
• B. It increases by two percent per 1,000 feet
• C. It remains constant
• D. It decreases by eight percent per 1,000 feet

Answer: (A)

As you gain altitude, the air grows thinner, which means the burner faces less dense air and slightly lower oxygen content per volume. That makes combustion a bit less efficient and reduces how effectively the heat from the burner is transferred to the balloon air. Because of these changing conditions, burner efficiency generally drops with altitude. The commonly cited figure is about a four percent decrease for every 1,000 feet climbed. So the best answer is that efficiency decreases by a small amount per thousand feet.

This isn’t a constant or increasing efficiency with altitude, and the drop isn’t as large as eight percent per thousand feet, which is why those other options don’t fit. In flight, pilots compensate by running the burner a bit longer or more to maintain the same lift as altitude increases.