The discharge from boiler relief valves must enter indirect waste through which component?

• A. A trap
• B. A check valve
• C. An air-gap
• D. A vent

Answer: (C)

Air gaps are used to prevent backflow when boiler relief valve discharge enters the indirect waste system. The relief valve can release hot water or steam, and if there were a direct or blocked path back toward the potable water supply, contaminants or scalding could be drawn back into the system. An air gap creates a physical separation between the discharge outlet and the receiving receptor, so wastewater cannot siphon back into the building’s plumbing.

Indirect waste means the discharge goes to a receptor (like a floor sink or standpipe) that is not directly connected to the sanitary sewer, with the air gap maintaining that safe separation. Other arrangements don’t meet this requirement: a trap isn’t used here for this purpose, a check valve could fail or create back-pressure issues, and a vent would vent to the atmosphere without preventing backflow into the potable system.