NATE Gas Heating (Air) Service Technician
Practice Exam Questions And Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. A gas furnace is not igniting. Which of the following is the most likely
cause?
A. Dirty air filter
B. Malfunctioning thermostat
C. Faulty ignitor
D. Clogged condensate line
Rationale: A faulty ignitor prevents the furnace from lighting, which
is a common ignition issue.
2. What is the typical color of a properly burning natural gas flame?
A. Red
B. Yellow
C. Blue
, D. Orange
Rationale: A blue flame indicates complete combustion, which is
normal for natural gas.
3. The primary function of a heat exchanger in a gas furnace is to:
A. Filter air
B. Transfer heat from combustion gases to air
C. Control gas pressure
D. Regulate airflow
Rationale: The heat exchanger allows heat from combustion gases to
transfer to the air circulating in the ductwork without mixing
combustion products.
4. A pressure switch in a furnace is designed to:
A. Measure supply voltage
B. Ensure the inducer motor is operating before ignition
C. Control fan speed
D. Adjust thermostat calibration
Rationale: The pressure switch ensures that the inducer motor has
created the proper draft for safe ignition.
5. Which of the following is the most common cause of a cracked heat
exchanger?
A. High gas pressure
B. Improper venting
C. Excessive temperature cycling
, D. Low airflow
Rationale: Repeated heating and cooling cycles can cause metal
fatigue, leading to cracks in the heat exchanger.
6. A gas furnace’s draft inducer motor fails to start. What should a
technician check first?
A. Thermostat batteries
B. Gas pressure
C. Electrical supply to the inducer motor
D. Air filter
Rationale: The inducer motor requires power to operate; verifying
electrical supply is the first troubleshooting step.
7. In a gas furnace, what is the purpose of the limit switch?
A. Start the gas valve
B. Measure thermostat setpoint
C. Prevent overheating by shutting off the burners
D. Control blower speed
Rationale: The limit switch turns off the burners if the furnace
exceeds safe temperatures.
8. Carbon monoxide can be produced in a gas furnace due to:
A. Dirty air filter
B. Low airflow
C. Incomplete combustion
D. High outdoor temperature
, Rationale: Incomplete combustion can produce carbon monoxide,
which is dangerous and indicates a malfunctioning furnace.
9. Which tool is most appropriate to measure the manifold gas pressure?
A. Multimeter
B. Manometer
C. Thermometer
D. Clamp meter
Rationale: A manometer measures gas pressure accurately for
furnace diagnostics.
10. What is the function of a gas valve in a furnace?
A. Adjust blower speed
B. Control the flow of gas to the burners
C. Regulate airflow
D. Measure combustion efficiency
Rationale: The gas valve opens and closes to allow gas to flow to the
burners when needed.
11. Which type of furnace venting requires a draft inducer motor?
A. Atmospheric venting
B. Forced draft venting
C. Direct venting
D. Power venting
Rationale: Forced draft venting uses an inducer motor to push flue
gases through the vent system.
Practice Exam Questions And Correct
Answers (Verified Answers) Plus Rationales
2026 Q&A | Instant Download Pdf
1. A gas furnace is not igniting. Which of the following is the most likely
cause?
A. Dirty air filter
B. Malfunctioning thermostat
C. Faulty ignitor
D. Clogged condensate line
Rationale: A faulty ignitor prevents the furnace from lighting, which
is a common ignition issue.
2. What is the typical color of a properly burning natural gas flame?
A. Red
B. Yellow
C. Blue
, D. Orange
Rationale: A blue flame indicates complete combustion, which is
normal for natural gas.
3. The primary function of a heat exchanger in a gas furnace is to:
A. Filter air
B. Transfer heat from combustion gases to air
C. Control gas pressure
D. Regulate airflow
Rationale: The heat exchanger allows heat from combustion gases to
transfer to the air circulating in the ductwork without mixing
combustion products.
4. A pressure switch in a furnace is designed to:
A. Measure supply voltage
B. Ensure the inducer motor is operating before ignition
C. Control fan speed
D. Adjust thermostat calibration
Rationale: The pressure switch ensures that the inducer motor has
created the proper draft for safe ignition.
5. Which of the following is the most common cause of a cracked heat
exchanger?
A. High gas pressure
B. Improper venting
C. Excessive temperature cycling
, D. Low airflow
Rationale: Repeated heating and cooling cycles can cause metal
fatigue, leading to cracks in the heat exchanger.
6. A gas furnace’s draft inducer motor fails to start. What should a
technician check first?
A. Thermostat batteries
B. Gas pressure
C. Electrical supply to the inducer motor
D. Air filter
Rationale: The inducer motor requires power to operate; verifying
electrical supply is the first troubleshooting step.
7. In a gas furnace, what is the purpose of the limit switch?
A. Start the gas valve
B. Measure thermostat setpoint
C. Prevent overheating by shutting off the burners
D. Control blower speed
Rationale: The limit switch turns off the burners if the furnace
exceeds safe temperatures.
8. Carbon monoxide can be produced in a gas furnace due to:
A. Dirty air filter
B. Low airflow
C. Incomplete combustion
D. High outdoor temperature
, Rationale: Incomplete combustion can produce carbon monoxide,
which is dangerous and indicates a malfunctioning furnace.
9. Which tool is most appropriate to measure the manifold gas pressure?
A. Multimeter
B. Manometer
C. Thermometer
D. Clamp meter
Rationale: A manometer measures gas pressure accurately for
furnace diagnostics.
10. What is the function of a gas valve in a furnace?
A. Adjust blower speed
B. Control the flow of gas to the burners
C. Regulate airflow
D. Measure combustion efficiency
Rationale: The gas valve opens and closes to allow gas to flow to the
burners when needed.
11. Which type of furnace venting requires a draft inducer motor?
A. Atmospheric venting
B. Forced draft venting
C. Direct venting
D. Power venting
Rationale: Forced draft venting uses an inducer motor to push flue
gases through the vent system.
