InterNACHI HVAC Systems Analysis 4 — Questions and Answers
Question 1: What does AFUE measure in heating equipment?
- Air flow uniformity efficiency
- Annual fuel utilization efficiency (Correct answer)
- Average furnace utility expenditure
- Airside fan unit efficiency
Correct answer: Annual fuel utilization efficiency
AFUE (Annual Fuel Utilization Efficiency) expresses as a percentage how much of the fuel's energy is converted to usable heat over a heating season.
Question 2: Which venting category applies to high-efficiency condensing furnaces with AFUE ≥90%?
- Category I (negative pressure, non-condensing)
- Category II (positive pressure, condensing)
- Category III (positive pressure, non-condensing)
- Category IV (positive pressure, condensing) (Correct answer)
Correct answer: Category IV (positive pressure, condensing)
Category IV applies to positive-pressure, condensing appliances like high-efficiency furnaces, which vent with PVC or CPVC pipe and produce acidic condensate.
Question 3: An inspector observes ice forming on the evaporator coil of a central AC system. Which condition is NOT a likely cause?
- Low refrigerant charge
- Restricted airflow from a dirty filter
- Oversized ductwork (Correct answer)
- Low outdoor ambient temperature during operation
Correct answer: Oversized ductwork
Oversized ductwork increases airflow, which would reduce icing; low refrigerant, restricted airflow, and operating below 65°F are all common causes of evaporator coil icing.
Question 4: What is the function of a humidistat in an HVAC system?
- It controls the blower motor speed based on humidity
- It activates or deactivates the humidifier based on indoor relative humidity (Correct answer)
- It measures refrigerant moisture content
- It triggers the dehumidifier when outdoor humidity exceeds 80%
Correct answer: It activates or deactivates the humidifier based on indoor relative humidity
A humidistat senses indoor relative humidity and signals the whole-house humidifier to operate when humidity falls below the set point.
Question 5: During an HVAC inspection, what does a home inspector typically verify about the condensate drain system?
- Refrigerant pressure at the drain valve
- That the primary drain is clear and a secondary drain or overflow switch is present (Correct answer)
- That the drain line discharges to the sanitary sewer only
- Drain pipe diameter matches the compressor BTU rating
Correct answer: That the primary drain is clear and a secondary drain or overflow switch is present
Inspectors verify the primary drain is unobstructed and that a secondary overflow drain or float switch exists to prevent water damage if the primary drain clogs.
Question 6: Which type of heat pump extracts heat energy from groundwater or the earth rather than outdoor air?
- Ductless mini-split heat pump
- Geothermal (ground-source) heat pump (Correct answer)
- Variable refrigerant flow (VRF) system
- Dual-fuel heat pump
Correct answer: Geothermal (ground-source) heat pump
Geothermal (ground-source) heat pumps use the stable temperature of the ground or groundwater as a heat source in winter and a heat sink in summer.
Question 7: What is the standard InterNACHI recommendation when a home inspector cannot fully evaluate a component of the HVAC system?
- Mark it as satisfactory and move on
- Skip it entirely and note it was inaccessible
- Report it as inaccessible or unable to be inspected and recommend further evaluation by a qualified HVAC technician (Correct answer)
- Estimate its condition based on the age of the system
Correct answer: Report it as inaccessible or unable to be inspected and recommend further evaluation by a qualified HVAC technician
InterNACHI standards require inspectors to report any system or component that could not be inspected and to recommend specialist evaluation when warranted.
InterNACHI HVAC Systems Analysis 4
What does AFUE measure in heating equipment?