For an oil-fired appliance with a mechanical draft, the horizontal termination point must be at least how many feet from an interior corner of two perpendicular walls?

• A. 1
• B. 2
• C. 3
• D. 6

Answer: (C)

When you vent horizontally from an oil-fired appliance with mechanical draft, keeping a clearance from the interior corner formed by two perpendicular walls is essential to prevent the exhaust plume from being deflected back toward openings or toward heat-sensitive surfaces. The standard minimum distance is three feet. This spacing helps ensure the combustion products disperse cleanly in free air and reduces the risk of re-entering the building or causing heat damage near the corner. Being closer than three feet increases the chance that the hot exhaust or moisture could affect nearby openings or materials, while a much larger distance isn’t required for this purpose under typical conditions.