Commercial appliance exhaust outlets that terminate above roof shall have the discharge opening located not less than how many inches above the roof surface?

• A. 30 inches
• B. 40 inches
• C. 50 inches
• D. 60 inches

Answer: (B)

The key idea is ensuring the exhaust plume has enough vertical clearance to disperse properly and not be drawn back into the building or into other roof openings. Releasing above the roof at a height of forty inches or more helps prevent recirculation of the exhaust by wind, avoids sooting or splashback onto the roof, and keeps the discharge away from any pedestrian areas or roof intakes. Forty inches is the minimum height that provides this safe, effective dispersion without adding unnecessary height or cost.