What is the maximum length of a natural draft horizontal chimney connector for fuel oil?

• A. 5 feet
• B. 15 feet
• C. 10 feet
• D. 20 feet

Answer: (C)

When venting a fuel oil appliance with natural draft, the path the exhaust takes to the chimney must not be too long or too horizontal. Hot flue gases rely on buoyancy to rise up the chimney, and any horizontal run adds friction losses and the potential for condensate to form or for backdrafts to occur. Limiting the vent connector length helps maintain a reliable draft so combustion gases aren’t pushed back into the space and the chimney can carry them away effectively. For fuel oil with natural draft, the accepted maximum horizontal length is 10 feet, so keeping the connector within that distance helps ensure safe, proper venting. If the install would require a longer run, you’d typically need to adjust the venting path to become shorter or use a mechanical draft inducer or a different venting arrangement.