InterNACHI Plumbing & HVAC Systems 5 — Questions and Answers
Question 1: What condition does an inspector suspect when they find the area around a toilet base is soft, stained, or the flooring feels spongy?
- Condensation from a cold tank
- A failed wax ring seal causing chronic leakage (Correct answer)
- Excessive toilet flush pressure
- An undersized supply line
Correct answer: A failed wax ring seal causing chronic leakage
A failed wax ring allows sewage and water to leak at the base of the toilet with each flush, leading to floor rot, mold, and structural damage over time.
Question 2: When inspecting a heat pump, what does it mean when the outdoor unit is running but the indoor air handler is blowing cool — not warm — air in heating mode?
- The system is in defrost cycle and will recover shortly
- The reversing valve may be stuck in cooling mode (Correct answer)
- The thermostat is set incorrectly to 'cool'
- The filter is excessively dirty
Correct answer: The reversing valve may be stuck in cooling mode
The reversing valve switches refrigerant flow direction to provide heating; if stuck in the cooling position, the system cools rather than heats even with the thermostat calling for heat.
Question 3: What is the purpose of a trap primer on a floor drain in a seldom-used area?
- To clean the drain automatically with chemicals
- To add water periodically to keep the trap seal from evaporating (Correct answer)
- To prevent backflow from the municipal sewer
- To reduce drain pipe corrosion
Correct answer: To add water periodically to keep the trap seal from evaporating
Floor drain traps in low-use areas can evaporate dry over time, allowing sewer gas entry; a trap primer automatically introduces small amounts of water to maintain the seal.
Question 4: An inspector observes white mineral deposits (scale) heavily coating the inside of a removed water heater anode rod. What does this indicate?
- The anode rod is functioning perfectly and has years of life remaining
- The water supply has high mineral content (hard water) and the anode may be depleted (Correct answer)
- The water heater is overheating
- Chlorine in the water reacted with the anode material
Correct answer: The water supply has high mineral content (hard water) and the anode may be depleted
Heavy scale buildup on an anode rod indicates hard water conditions and signals the rod may be near or at end of life, leaving the tank vulnerable to corrosion.
Question 5: Which HVAC filter MERV rating provides the best balance of particle removal and adequate airflow for most residential forced-air systems?
- MERV 1–4
- MERV 8–11 (Correct answer)
- MERV 13–16
- MERV 17–20
Correct answer: MERV 8–11
MERV 8–11 filters capture most common household particles including dust mite debris, mold spores, and pet dander without excessively restricting airflow in residential systems.
Question 6: What does a home inspector note when a plumbing vent pipe terminates below the roof line or inside an attic?
- It is acceptable if the attic is ventilated
- Sewer gases will accumulate in the attic or living space — a code defect (Correct answer)
- Only a concern if the attic is conditioned space
- It reduces roof penetrations, which is preferred
Correct answer: Sewer gases will accumulate in the attic or living space — a code defect
Plumbing vent pipes must terminate through and above the roof to discharge sewer gases to the exterior; terminating inside an attic allows toxic and flammable gases to accumulate.
Question 7: An inspector finds a furnace flue pipe that pitches downward toward the furnace rather than upward toward the chimney. Why is this a defect?
- Horizontal runs are prohibited for gas appliances
- Condensate and combustion gases will not draft properly and can back-flow into the home (Correct answer)
- The pipe diameter is too small for the pitch angle
- It prevents adequate combustion air from entering the burner
Correct answer: Condensate and combustion gases will not draft properly and can back-flow into the home
Flue pipes must maintain an upward pitch (minimum 1/4 inch per foot) toward the chimney so that buoyant combustion gases — including carbon monoxide — rise and exit rather than back-drafting.
InterNACHI Plumbing & HVAC Systems 5
What condition does an inspector suspect when they find the area around a toilet base is soft, stained, or the flooring feels spongy?