InterNACHI - International Association of Certified Home Inspectors Plumbing Systems Inspection Questions and Answers — Questions and Answers
Question 1: An inspector, while evaluating a home's drain, waste, and vent (DWV) system, hears a distinct gurgling sound from the bathtub drain immediately after flushing a nearby toilet. Both fixtures appear to drain adequately otherwise. What is the most probable cause of this gurgling sound?
- Excessive water pressure in the supply lines.
- A cracked toilet bowl.
- A partial blockage or inadequate plumbing vent. (Correct answer)
- The P-trap for the bathtub has lost its seal due to evaporation.
Correct answer: A partial blockage or inadequate plumbing vent.
Gurgling sounds from adjacent fixtures are a classic sign of a venting problem. When the toilet is flushed, a large volume of water rushing down the drain creates negative pressure. If the vent stack is blocked or improperly installed, the system will draw air from the easiest source, which is often through the P-trap of a nearby fixture like a bathtub, causing the water in the trap to gurgle.
Question 2: What is the primary safety purpose of the Temperature and Pressure Relief (TPR) valve installed on a residential water heater?
- To prevent dangerous pressure or temperature buildup by discharging water. (Correct answer)
- To allow the homeowner to easily drain the tank for routine maintenance.
- To automatically regulate the daily operating temperature of the water.
- To prevent sediment from accumulating at the bottom of the tank.
Correct answer: To prevent dangerous pressure or temperature buildup by discharging water.
The TPR valve is a critical safety device designed to open automatically if either the temperature (typically >210°F) or the pressure (typically >150 psi) inside the tank exceeds safe limits. By discharging water, it prevents a potentially catastrophic explosion.
Question 3: During an inspection of a home built in 1988, an inspector identifies flexible, gray plastic water supply pipes stamped with "PB2110." This piping material is known as:
- Cross-linked polyethylene (PEX)
- Chlorinated polyvinyl chloride (CPVC)
- Acrylonitrile butadiene styrene (ABS)
- Polybutylene (PB) (Correct answer)
Correct answer: Polybutylene (PB)
Polybutylene (PB) is a type of plastic piping, often gray and marked with the code "PB2110," that was used extensively from the late 1970s to the mid-1990s. It is known to degrade when exposed to oxidants in public water supplies, becoming brittle and failing without warning, which led to class-action lawsuits and its removal from building codes.
Question 4: While inspecting a home's exterior, you observe a garden hose attached to a hose bibb with the other end of the hose lying submerged in a small, decorative pond. This situation represents a significant risk known as a:
- Pressure differential failure
- Hydraulic displacement defect
- Cross-connection with a potential for back-siphonage (Correct answer)
- Thermal expansion overload
Correct answer: Cross-connection with a potential for back-siphonage
This is a classic example of a cross-connection, where the potable water supply is potentially connected to a source of contamination. If a pressure drop occurs in the main supply line (e.g., due to a water main break or firefighting), contaminated water from the pond could be siphoned back into the home's drinking water.
Question 5: According to common plumbing codes, a P-trap is installed at each fixture to block sewer gases from entering the home. What is the generally accepted minimum and maximum water seal depth for a standard P-trap?
- 1 inch minimum, 3 inches maximum
- 2 inches minimum, 4 inches maximum (Correct answer)
- 4 inches minimum, 6 inches maximum
- 0.5 inches minimum, 2 inches maximum
Correct answer: 2 inches minimum, 4 inches maximum
Most plumbing codes specify that a standard fixture P-trap must maintain a water seal of at least 2 inches to be effective against sewer gas and no more than 4 inches. A seal deeper than 4 inches can slow drainage and make it more likely to trap debris, while a seal less than 2 inches is more susceptible to evaporation or being siphoned out.
Question 6: Which of the following actions is an inspector REQUIRED to perform during a plumbing inspection according to the InterNACHI Standards of Practice?
- Determine the potability or quality of the water.
- Describe the materials of the visible water supply and drain lines. (Correct answer)
- Operate any shut-off valves to confirm they are functional.
- Measure the water pressure using a gauge.
Correct answer: Describe the materials of the visible water supply and drain lines.
The InterNACHI Standards of Practice require the inspector to inspect and describe the visible water supply and distribution piping materials, as well as the drain, waste, and vent piping materials. The standards explicitly state the inspector is NOT required to determine water quality, operate shut-off valves, or measure water pressure.
InterNACHI - International Association of Certified Home Inspectors Plumbing Systems Inspection Questions and Answers
An inspector, while evaluating a home's drain, waste, and vent (DWV) system, hears a distinct gurgling sound from the bathtub drain immediately after flushing a nearby toilet.
Both fixtures appear to drain adequately otherwise.
What is the most probable cause of this gurgling sound?