Home Inspector Forced-Air Furnace Inspection Flashcards
7 cards from real Home Inspector Test practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Home Inspector Forced-Air Furnace Inspection flashcards as text
When inspecting a high-efficiency condensing furnace, the inspector finds the PVC vent pipe is not supported and sags between connection points. Why is this a defect?
Answer: Sagging can allow condensate to pool and block flue gas flow
Condensing furnace vent pipes must be properly supported and pitched to drain condensate; sagging creates traps that can block the flue and cause the furnace to shut down or back-draft.
The thermocouple or flame sensor in a gas furnace is designed to do what if it fails to detect a flame?
Answer: Signal the control board to lock out and stop gas flow
The flame sensor sends a signal proving ignition; if it fails to sense a flame within a set period, the control board shuts off the gas valve to prevent unburned gas accumulation.
A home inspector tests the furnace and notices it cycles on and off very frequently without reaching the setpoint temperature. This is called:
Answer: Short cycling
Short cycling occurs when the furnace turns on and off more frequently than normal, often due to overheating, a dirty filter, or a faulty limit switch.
What is the function of the high-limit switch in a forced-air furnace?
Answer: It shuts off the burner if the supply air temperature exceeds a safe threshold
The high-limit switch monitors heat exchanger temperature and shuts down the burner if temperatures exceed safe limits, protecting against overheating.
An inspector finds a furnace filter that is heavily clogged with debris. What is the most likely consequence if left uncorrected?
Answer: Reduced airflow causing overheating and possible heat exchanger damage
A severely restricted filter reduces airflow across the heat exchanger, causing it to overheat, which can trigger the limit switch and over time crack the heat exchanger.
What material is NOT acceptable for use as a furnace flue connector in a Category I (negative pressure, non-condensing) gas appliance?
Answer: PVC plastic pipe
PVC is only approved for Category IV (positive pressure, condensing) appliances; using it on a Category I furnace is a code violation and safety hazard.
When a home inspector operates the furnace and notices a strong smell of aldehydes or a sharp acrid odor from the supply registers, what should be suspected?
Answer: A cracked heat exchanger allowing combustion gases into the airstream
Aldehydes and acrid odors in supply air during furnace operation are classic indicators of a compromised heat exchanger leaking combustion gases.