InterNACHI Plumbing & HVAC Systems 2 — Questions and Answers
Question 1: What is the minimum slope required for a horizontal drain pipe to ensure proper drainage by gravity?
- 1/16 inch per foot
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
Correct answer: 1/4 inch per foot
A minimum slope of 1/4 inch per foot (2%) is required for horizontal drain pipes 3 inches or smaller to maintain adequate flow velocity.
Question 2: A home inspector observes a water heater with no pressure relief valve discharge pipe. What is the primary concern?
- It violates cosmetic standards
- Steam and hot water could spray dangerously if the valve opens (Correct answer)
- The valve will not function at all
- Cold water will back-siphon into the tank
Correct answer: Steam and hot water could spray dangerously if the valve opens
Without a discharge pipe, an opening T&P valve could spray scalding water or steam directly at occupants, posing a serious burn hazard.
Question 3: What does a home inspector look for when checking an air conditioning evaporator coil?
- Rust-colored refrigerant lines
- Ice buildup or blocked condensate drain (Correct answer)
- High-pitched motor noise
- Oversized return-air grille
Correct answer: Ice buildup or blocked condensate drain
Ice on the evaporator coil indicates restricted airflow or low refrigerant, and a blocked condensate drain can cause water damage or system shutdown.
Question 4: Which type of pipe is most commonly identified by its blue or black color and is acceptable for potable cold-water supply lines?
- CPVC
- PEX (Correct answer)
- ABS
- Cast iron
Correct answer: PEX
PEX (cross-linked polyethylene) is commonly color-coded blue for cold water and red for hot water, and is approved for potable water supply.
Question 5: An inspector finds a gas furnace with a cracked heat exchanger. What is the recommended course of action?
- Note it for future monitoring
- Seal the crack with furnace cement before re-inspection
- Recommend immediate discontinuation of use and professional repair (Correct answer)
- Increase combustion air supply to compensate
Correct answer: Recommend immediate discontinuation of use and professional repair
A cracked heat exchanger can allow carbon monoxide to mix with supply air and enter living spaces, making it a life-safety issue requiring immediate action.
Question 6: What is the purpose of a backflow preventer on a hose bibb (exterior faucet)?
- To regulate water pressure at the outlet
- To prevent contaminated water from siphoning back into the potable supply (Correct answer)
- To shut off flow automatically in freezing conditions
- To filter sediment from outdoor water
Correct answer: To prevent contaminated water from siphoning back into the potable supply
A backflow preventer (vacuum breaker) stops contaminated water — such as from a garden hose left in a chemical solution — from being siphoned back into the home's potable water supply.
Question 7: When inspecting supply ducts in an unconditioned attic, an inspector should be most concerned about:
- Duct color fading from UV exposure
- Missing or inadequate insulation on ducts (Correct answer)
- Rectangular versus round duct shape
- Number of duct branches per trunk line
Correct answer: Missing or inadequate insulation on ducts
Uninsulated ducts in a hot attic lose significant conditioned air energy and can cause condensation, reducing system efficiency and potentially causing moisture damage.
InterNACHI Plumbing & HVAC Systems 2
What is the minimum slope required for a horizontal drain pipe to ensure proper drainage by gravity?