CBI Plumbing & Mechanical Inspection — Questions and Answers
Question 1: What is the purpose of a plumbing trap?
- To hold water that creates a seal preventing sewer gases from entering the building through drain openings (Correct answer)
- To catch dropped items like jewelry
- To filter debris from wastewater
- To increase water pressure
Correct answer: To hold water that creates a seal preventing sewer gases from entering the building through drain openings
P-traps and S-traps hold a water seal (2-4 inches) in the curved pipe section, blocking toxic and flammable sewer gases from entering habitable spaces through drain openings.
Question 2: What is the minimum slope required for horizontal drain pipes?
- 1/4 inch per foot for pipes 3 inches or smaller; 1/8 inch per foot for pipes larger than 3 inches (Correct answer)
- Level (no slope required)
- 1 inch per foot for all pipes
- 2 inches per foot for all pipes
Correct answer: 1/4 inch per foot for pipes 3 inches or smaller; 1/8 inch per foot for pipes larger than 3 inches
Proper slope ensures wastewater flows by gravity without flowing too fast (which leaves solids behind) or too slow (which causes clogs). Quarter-inch per foot is standard for most residential drain pipes.
Question 3: What is a plumbing vent and why is it necessary?
- A pipe extending to the roof that allows air into the drainage system to maintain proper flow and prevent siphoning of traps (Correct answer)
- A ventilation fan in the bathroom
- An air conditioning duct
- A window in the bathroom
Correct answer: A pipe extending to the roof that allows air into the drainage system to maintain proper flow and prevent siphoning of traps
Plumbing vents allow air to enter the drainage system, equalizing pressure so waste flows freely and preventing the vacuum effect that would siphon water from traps, allowing sewer gases to enter.
Question 4: What should an inspector verify during an HVAC rough-in inspection?
- Correct ductwork sizing, proper support, sealed connections, refrigerant line insulation, and compliance with mechanical code (Correct answer)
- Only the thermostat location
- Whether the HVAC brand is approved
- Only the exterior condenser placement
Correct answer: Correct ductwork sizing, proper support, sealed connections, refrigerant line insulation, and compliance with mechanical code
HVAC rough-in inspections verify duct sizing for adequate airflow, proper hanging/support, sealed joints, fire dampers at penetrations, refrigerant line specifications, condensate drainage, and code-required clearances.
Question 5: What is the purpose of a water heater temperature and pressure (T&P) relief valve?
- To release water and pressure if the tank overheats or becomes over-pressurized, preventing a tank explosion (Correct answer)
- To regulate the temperature of hot water at faucets
- To test water quality
- To drain the tank for maintenance
Correct answer: To release water and pressure if the tank overheats or becomes over-pressurized, preventing a tank explosion
The T&P valve is a critical safety device that opens automatically if water temperature exceeds 210°F or pressure exceeds 150 PSI, preventing the catastrophic failure (explosion) of the water heater tank.
Question 6: Where must a water heater T&P relief valve discharge line terminate?
- To the exterior of the building or to an approved indirect waste receptor, within 6 inches of the floor (Correct answer)
- Into the drain system
- Back into the water heater
- Into the attic space
Correct answer: To the exterior of the building or to an approved indirect waste receptor, within 6 inches of the floor
The discharge pipe must terminate where released hot water will not cause injury or damage: typically outside the building or to an approved drain, within 6 inches of the floor, and without being threaded, reduced, or trapped.
CBI Plumbing & Mechanical Inspection
What is the purpose of a plumbing trap?