HVAC Flashcards
7 cards from real NHIE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 HVAC flashcards as text
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?
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.
What does AFUE stand for and what does it measure in a heating system?
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.
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?
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.
A home inspector observes that a furnace heat exchanger has visible cracks. What is the PRIMARY safety concern?
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.
What is the recommended minimum clearance between a gas-fired furnace and combustible materials?
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.
Which type of thermostat wire color is typically used for the common (C) wire in a modern HVAC system?
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.
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?
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.