A plumber is inspecting a newly installed plumbing system in a single-family dwelling. They notice that a combination waste and vent system has been used for the kitchen sink and dishwasher, which are located on the ground floor. The horizontal wet vent section is 3 metres long and serves a total of 4 drainage fixture units. What is the minimum nominal pipe size required for this combination waste and vent according to the National Plumbing Code of Canada?

Question: A plumber is inspecting a newly installed plumbing system in a single-family dwelling. They notice that a combination waste and vent system has been used for the kitchen sink and dishwasher, which are located on the ground floor. The horizontal wet vent section is 3 metres long and serves a total of 4 drainage fixture units. What is the minimum nominal pipe size required for this combination waste and vent according to the National Plumbing Code of Canada?

Answer options:

• 38 mm
• 51 mm ✅ 64 mm
• 76 mm

Correct answer: 64 mm

Explanation: According to the National Plumbing Code of Canada, for a combination waste and vent system serving 4 drainage fixture units, the minimum nominal pipe size must be 64 mm (2 1/2 inches). A 38 mm or 51 mm pipe would be undersized for this application, especially for a wet vent carrying both waste and air.