A plumber is retrofitting a domestic hot water tank in a residential home. The existing relief valve discharge pipe terminates directly into a floor drain, creating an air gap of 15 mm. According to the NPC, what is the minimum required air gap for a connection to an indirect waste receptacle?

Question: A plumber is retrofitting a domestic hot water tank in a residential home. The existing relief valve discharge pipe terminates directly into a floor drain, creating an air gap of 15 mm. According to the NPC, what is the minimum required air gap for a connection to an indirect waste receptacle?

Answer options:

• 10 mm
• 12.7 mm ✅ 25 mm
• 38 mm

Correct answer: 25 mm

Explanation: The National Plumbing Code of Canada (NPC) specifies that the air gap for connections to indirect waste receptacles must be at least twice the diameter of the effective opening of the pipe, but not less than 25 mm. Therefore, 15 mm is insufficient, and the minimum required air gap is 25 mm.