InterNACHI HVAC Systems Analysis 5 — Questions and Answers
Question 1: Which condition is most commonly associated with a failed or dirty flame sensor in a gas furnace?
- The furnace never starts
- The furnace lights briefly then shuts off after a few seconds (Correct answer)
- The furnace runs continuously without reaching setpoint
- The heat exchanger overheats repeatedly
Correct answer: The furnace lights briefly then shuts off after a few seconds
A dirty or failed flame sensor cannot confirm ignition, causing the control board to shut off the gas valve within seconds as a safety measure.
Question 2: What is the primary purpose of a whole-house bypass humidifier bypass duct?
- To allow excess humidity to escape outdoors
- To route a portion of supply air through the humidifier pad and back to the return plenum (Correct answer)
- To equalize static pressure across supply and return ducts
- To prevent furnace backdrafting during high humidity conditions
Correct answer: To route a portion of supply air through the humidifier pad and back to the return plenum
A bypass humidifier draws warm supply air through a water-saturated evaporative pad and returns the humidified air to the return plenum for distribution.
Question 3: A home inspector observes that a split-system AC compressor is located in a utility closet inside the home. What is the most significant concern?
- Limited access for future service
- The condenser coil cannot reject heat properly indoors, making the system ineffective (Correct answer)
- Noise transmission to living areas
- The refrigerant lines will be too short
Correct answer: The condenser coil cannot reject heat properly indoors, making the system ineffective
Air-cooled condensing units must be outdoors to reject heat to the atmosphere; placing one indoors prevents proper heat rejection and will cause the system to fail.
Question 4: Which HVAC filter rating system measures a filter's ability to capture particles of specific sizes?
- SEER rating
- AFUE rating
- MERV rating (Correct answer)
- EER rating
Correct answer: MERV rating
MERV (Minimum Efficiency Reporting Value) rates filter efficiency from 1–16 based on the percentage of particles captured at different sizes.
Question 5: During an inspection of a packaged rooftop HVAC unit, what should the inspector note about the unit's curb?
- The color of the curb coating
- Whether the curb is properly flashed and sealed to prevent roof leaks (Correct answer)
- The BTU capacity stamped on the curb
- Whether the curb is painted to match the roofing material
Correct answer: Whether the curb is properly flashed and sealed to prevent roof leaks
Improper flashing or sealing around a rooftop unit curb is a leading cause of roof leaks and should be reported if deteriorated or improperly installed.
Question 6: What is the typical expected service life of a residential gas furnace?
- 5–10 years
- 10–15 years
- 15–20 years (Correct answer)
- 25–30 years
Correct answer: 15–20 years
The average service life of a residential gas furnace is approximately 15–20 years, with proper maintenance extending that range.
Question 7: When inspecting a zoned HVAC system, what component regulates airflow to individual zones?
- Variable speed compressor
- Motorized dampers controlled by zone thermostats (Correct answer)
- Multiple air handlers sharing one condenser
- Bypass relief valves in the return plenum
Correct answer: Motorized dampers controlled by zone thermostats
Motorized dampers in the ductwork open or close based on signals from individual zone thermostats, allowing each zone to be heated or cooled independently.
InterNACHI HVAC Systems Analysis 5
Which condition is most commonly associated with a failed or dirty flame sensor in a gas furnace?