InterNACHI Plumbing & HVAC Systems 3 — Questions and Answers
Question 1: Which condition in a plumbing system is described as water hammer?
- Slow drain caused by grease buildup
- Banging noise when a valve or faucet is quickly shut off (Correct answer)
- Gurgling sound from a dry P-trap
- Whistling noise from a partially open shut-off valve
Correct answer: Banging noise when a valve or faucet is quickly shut off
Water hammer is the banging or thudding sound caused by the sudden pressure wave when fast-moving water is abruptly stopped by a closing valve.
Question 2: What does AFUE stand for in reference to heating equipment, and what does a higher number indicate?
- Annual Fuel Utilization Efficiency; higher means more efficient (Correct answer)
- Adjusted Furnace Unit Efficiency; higher means more BTU output
- Average Fuel Usage Estimate; higher means more fuel consumed
- Airflow Furnace Unit Efficiency; higher means better air distribution
Correct answer: Annual Fuel Utilization Efficiency; higher means more efficient
AFUE (Annual Fuel Utilization Efficiency) measures how much fuel is converted to heat; a rating of 95% means 95% of fuel energy becomes useful heat.
Question 3: An inspector notices that a bathroom exhaust fan vents into the attic instead of to the exterior. What is the concern?
- It will cause elevated electric bills
- Moisture and mold can accumulate in the attic (Correct answer)
- The fan motor will overheat
- It reduces combustion air to the furnace
Correct answer: Moisture and mold can accumulate in the attic
Exhausting humid bathroom air into an attic introduces moisture that can lead to condensation, wood rot, and mold growth on framing and sheathing.
Question 4: What is the minimum required distance between a gas water heater's pilot or burner and the floor in a garage installation?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
In a garage, ignition sources such as pilot lights must be elevated at least 18 inches above the floor to reduce the risk of igniting gasoline vapors that pool low.
Question 5: Which refrigerant was widely phased out of residential air conditioning systems due to ozone depletion concerns?
- R-410A
- R-22 (Freon) (Correct answer)
- R-32
- R-744 (CO₂)
Correct answer: R-22 (Freon)
R-22 (chlorodifluoromethane, marketed as Freon) was phased out under the Clean Air Act because its chlorine atoms deplete stratospheric ozone.
Question 6: A home inspector observes galvanic corrosion where copper pipe connects directly to a steel fitting. What should be used to prevent this?
- Teflon tape
- A dielectric union or fitting (Correct answer)
- Solder paste only
- An additional shut-off valve
Correct answer: A dielectric union or fitting
A dielectric union or fitting isolates dissimilar metals electrically, preventing the electrochemical reaction that causes accelerated corrosion at the joint.
Question 7: What is the function of a condensate neutralizer on a high-efficiency condensing furnace?
- It filters particulates from flue gas
- It raises the pH of acidic condensate before it enters the drain (Correct answer)
- It separates water from combustion air
- It reduces static pressure in the flue
Correct answer: It raises the pH of acidic condensate before it enters the drain
High-efficiency furnaces produce acidic condensate (pH 2–4) that can damage cast-iron drains; a neutralizer raises the pH to a safe level before disposal.
InterNACHI Plumbing & HVAC Systems 3
Which condition in a plumbing system is described as water hammer?