Approximately how many cubic feet of combustion air are needed to burn one gallon of fuel oil?

• A. 1000 cu ft
• B. 1540 cu ft
• C. 500 cu ft
• D. 2000 cu ft

Answer: (B)

Combustion air per gallon of fuel oil can be estimated from the air–fuel ratio and the densities involved. For complete combustion of hydrocarbons, about 14.7 pounds of air are required for every 1 pound of fuel. Heating oil weighs roughly 7.5 pounds per gallon, so per gallon you’d need about 7.5 × 14.7 ≈ 110 pounds of air. Air density is about 0.075 pounds per cubic foot, so the air volume needed is 110 ÷ 0.075 ≈ 1467 cubic feet. In practice, burners use some excess air to ensure complete combustion; applying a small excess (around 5%) brings it to roughly 1540 cubic feet per gallon. So the approximate amount is about 1540 cubic feet.