The maximum size of an oil supply line shall be which of the following?

• A. 5/8 inch
• B. 3/4 inch
• C. 1/2 inch
• D. A+B

Answer: (D)

The size of an oil supply line is set by how much fuel the burner needs and how much pressure loss you can tolerate along the run. You want a line large enough to deliver the required flow, but not so large that regulators or other parts are out of their intended range. Because fuel demand varies with burner rating, run length, and system components, the upper limit for the supply line isn’t a single fixed number for every installation. In practice, both five-eighths inch and three-quarters inch supply lines are permissible as the maximum size, depending on the specific burner and installation requirements. If the burner has a higher firing rate or a longer run, a larger line may be needed; for smaller loads, a smaller line may suffice. Always match the line size to the burner’s data and local code guidance.