NHIE HVAC 2 — Questions and Answers
Question 1: A home inspector notices the flue pipe from a gas furnace is sloping downward toward the furnace. What is the correct slope requirement for a Category I furnace flue?
- Level is acceptable for horizontal runs
- Minimum 1/4 inch rise per foot toward the chimney (Correct answer)
- Minimum 1/2 inch rise per foot toward the chimney
- Any upward slope is acceptable regardless of angle
Correct answer: Minimum 1/4 inch rise per foot toward the chimney
Category I gas appliance flue pipes must slope upward at least 1/4 inch per foot toward the chimney to allow proper draft and prevent condensate from flowing back into the furnace.
Question 2: What does AFUE stand for and what does it measure in a heating system?
- Air Flow Unit Efficiency — measures airflow volume
- Annual Fuel Utilization Efficiency — measures seasonal heating efficiency (Correct answer)
- Adjusted Furnace Unit Emissions — measures combustion byproducts
- Average Furnace Usage Estimate — measures run-time hours
Correct answer: Annual Fuel Utilization Efficiency — measures seasonal heating efficiency
AFUE (Annual Fuel Utilization Efficiency) is the ratio of annual heat output to total annual fossil fuel energy consumed, expressed as a percentage.
Question 3: During inspection, an inspector finds a heat pump with ice forming on the outdoor unit in winter. Which condition would indicate a defect rather than normal operation?
- Light frost on the coil during normal heating cycle
- Ice melting during a defrost cycle
- Thick ice accumulation covering the entire coil with no defrost occurring (Correct answer)
- Brief icing immediately after startup in cold weather
Correct answer: Thick ice accumulation covering the entire coil with no defrost occurring
Thick ice covering the entire outdoor coil with no defrost cycle activating indicates a defrost control malfunction or refrigerant issue requiring service.
Question 4: A home inspector observes that a furnace heat exchanger has visible cracks. What is the PRIMARY safety concern?
- Reduced heating efficiency
- Carbon monoxide entering the living space through the air supply (Correct answer)
- Increased energy costs
- Premature blower motor failure
Correct answer: Carbon monoxide entering the living space through the air supply
A cracked heat exchanger allows combustion gases, including carbon monoxide, to mix with circulating air and be distributed throughout the living space, creating a life-safety hazard.
Question 5: What is the recommended minimum clearance between a gas-fired furnace and combustible materials?
- 1 inch on all sides
- As specified on the furnace manufacturer's label (Correct answer)
- 6 inches on all sides regardless of manufacturer specs
- 12 inches on top, 6 inches on sides
Correct answer: As specified on the furnace manufacturer's label
Clearance requirements vary by furnace model and design, so the manufacturer's installed label is the authoritative source that home inspectors must reference.
Question 6: Which type of thermostat wire color is typically used for the common (C) wire in a modern HVAC system?
- Red
- Green
- Yellow
- Blue or black (Correct answer)
Correct answer: Blue or black
The C-wire (common wire) is typically blue or black in color and provides a continuous 24V return path needed to power smart thermostats.
Question 7: An inspector finds that the condensate drain line from an air handler terminates directly into the floor drain without a trap. What is the concern?
- The drain line is too short
- Sewer gases can migrate up through the drain line into the air handler and living space (Correct answer)
- Floor drains are not approved for condensate disposal
- The drain line material may not be compatible with the floor drain
Correct answer: Sewer gases can migrate up through the drain line into the air handler and living space
Without a P-trap on the condensate drain line, sewer gases can travel back through the drain and into the air handler, potentially contaminating indoor air quality.
NHIE HVAC 2
A home inspector notices the flue pipe from a gas furnace is sloping downward toward the furnace.
What is the correct slope requirement for a Category I furnace flue?