Home Inspector Test Home Inspector Forced-Air Furnace Inspection 5 — Questions and Answers
Question 1: When inspecting a furnace, the inspector finds no sediment trap (drip leg) on the gas supply line. What is the significance?
- It is required only on commercial installations, not residential
- Without a sediment trap, debris and moisture can enter gas valve components, causing malfunction (Correct answer)
- A sediment trap is optional if a shutoff valve is present
- This only matters for propane systems, not natural gas
Correct answer: Without a sediment trap, debris and moisture can enter gas valve components, causing malfunction
A sediment trap (drip leg) catches debris and moisture before they can reach the gas valve or burner orifices; it is required by most codes on all gas appliance connections.
Question 2: What is the correct interpretation when a furnace's control board displays a fault code with two LED flashes followed by a pause?
- The furnace is operating normally in a two-stage heating mode
- A specific diagnostic code indicating a fault condition — the meaning must be looked up on the furnace's fault code chart (Correct answer)
- The primary limit switch has been reset and the furnace is ready
- The igniter is warming up and the furnace will fire within 30 seconds
Correct answer: A specific diagnostic code indicating a fault condition — the meaning must be looked up on the furnace's fault code chart
Modern furnace control boards use LED flash codes to communicate specific fault conditions; the home inspector should reference the fault code chart typically printed inside the furnace panel.
Question 3: A homeowner reports the furnace produces a loud bang or boom when it starts. What is the most likely cause?
- Normal thermal expansion of ductwork
- Delayed ignition causing gas to accumulate before igniting (Correct answer)
- The blower motor starting under load
- An oversized return air plenum
Correct answer: Delayed ignition causing gas to accumulate before igniting
Delayed ignition allows unburned gas to build up in the combustion chamber; when ignition finally occurs, the accumulated gas ignites with a bang — a condition that can damage the heat exchanger.
Question 4: What is the minimum vent clearance required between a Category I furnace vent termination and an operable window or door?
- 6 inches
- 12 inches
- 4 feet horizontally or 1 foot above (Correct answer)
- Clearances only apply to direct-vent appliances
Correct answer: 4 feet horizontally or 1 foot above
Most codes require the vent termination to be at least 4 feet horizontally from or 1 foot above any door, window, or gravity air inlet to prevent combustion gases from re-entering the home.
Question 5: A home inspector discovers the furnace filter slot has a bypass — air can flow around the filter entirely. What should be reported?
- This is intentional to prevent excessive restriction during high demand
- Unfiltered air bypassing the filter can cause heat exchanger fouling and reduced equipment life — the bypass should be sealed (Correct answer)
- Bypasses are acceptable if the filter is the high-MERV type
- This is only relevant if the occupant has allergies
Correct answer: Unfiltered air bypassing the filter can cause heat exchanger fouling and reduced equipment life — the bypass should be sealed
Air bypass around the filter sends unfiltered dust and debris through the blower and across the heat exchanger, accelerating wear and reducing efficiency.
Question 6: What does a home inspector look for at the furnace's return air plenum connection to identify a potential indoor air quality hazard?
- The plenum material should be sheet metal, not duct board
- Gaps or unsealed connections that could draw in air from unconditioned spaces like crawl spaces or garages (Correct answer)
- The plenum should be insulated to at least R-8
- Return plenums should always be located on the supply side of the furnace
Correct answer: Gaps or unsealed connections that could draw in air from unconditioned spaces like crawl spaces or garages
Unsealed return air plenums can draw in mold spores, radon, pesticides, or carbon monoxide from crawl spaces, attics, or garages and distribute them throughout the home.
Question 7: Which of the following best describes how a home inspector documents a furnace that is functional but has a minor safety concern such as a missing blower door panel?
- List it as informational with no action required
- Note it as a safety hazard requiring correction, with a recommendation to consult a licensed HVAC technician (Correct answer)
- Recommend immediate replacement of the entire furnace unit
- Do not report it since the furnace still produces heat
Correct answer: Note it as a safety hazard requiring correction, with a recommendation to consult a licensed HVAC technician
A missing blower door affects combustion air balance and safety; it should be documented as a safety deficiency requiring correction by a qualified technician.
Home Inspector Test Home Inspector Forced-Air Furnace Inspection 5
When inspecting a furnace, the inspector finds no sediment trap (drip leg) on the gas supply line.
What is the significance?