NATE Gas Heating Exam 2026/2027 –
Questions and Answers with
Rationales
Coverage: Gas Heating, Safety, Combustion, Furnaces, Controls, Venting,
Airflow, Installation, Service & Troubleshooting
SECTION 1 — SAFETY, CODES & SERVICE PRACTICES
1. Before servicing a gas furnace, the technician should first:
A. Increase the thermostat setting
B. Shut off the appropriate energy sources and follow safety procedures
C. Remove the blower assembly
D. Adjust the gas valve
Answer: B
Rationale: Gas and electrical energy must be controlled before service. Proper
lockout/tagout and manufacturer safety procedures reduce the risk of shock,
burns, fire, and unintended equipment operation.
2. The primary danger from incomplete combustion of natural gas is:
A. Oxygen enrichment
B. High humidity
C. Carbon monoxide production
D. Refrigerant migration
Answer: C
Rationale: Incomplete combustion can produce carbon monoxide (CO), a
colorless and potentially fatal gas.
,3. A technician should use a calibrated combustion analyzer primarily to:
A. Measure refrigerant pressure
B. Evaluate combustion and flue-gas characteristics
C. Measure blower RPM
D. Test capacitor capacitance
Answer: B
Rationale: A combustion analyzer measures parameters such as oxygen,
carbon monoxide, carbon dioxide, flue temperature, and efficiency-related
information.
4. If a strong gas odor is detected inside a building, the technician should:
A. Immediately operate electrical switches
B. Light a burner to locate the leak
C. Follow emergency gas-leak procedures and avoid ignition sources
D. Increase furnace airflow
Answer: C
Rationale: Gas accumulation can create an explosion hazard. Ignition sources,
including electrical switches and flames, should be avoided.
5. The purpose of a gas appliance sediment trap is to:
A. Increase manifold pressure
B. Collect debris or condensate before it enters the gas valve
C. Increase combustion temperature
D. Reduce blower noise
Answer: B
,Rationale: A sediment trap helps prevent contaminants from entering
sensitive gas-control components.
6. Which PPE is most appropriate when working around an operating gas
furnace?
A. Safety glasses and appropriate protective equipment
B. Sandals and cotton gloves only
C. No PPE because furnaces are low voltage
D. Hearing protection only
Answer: A
Rationale: Service work can involve electrical hazards, hot surfaces, sharp
metal, combustion gases, and moving components.
7. A technician should verify combustion safety after changing:
A. Thermostat batteries
B. Gas input, burner operation, or venting components
C. Filter size only
D. Condensate tubing color
Answer: B
Rationale: Changes affecting fuel input or combustion/venting can alter
combustion performance and safety.
8. Carbon monoxide detectors are intended to:
A. Replace proper furnace maintenance
B. Replace combustion testing
C. Provide an additional warning of dangerous CO levels
D. Control the gas valve
Answer: C
, Rationale: CO detectors provide supplemental protection but do not replace
proper appliance installation, maintenance, and combustion testing.
9. Which condition can contribute to incomplete combustion?
A. Proper combustion air
B. Correct gas pressure
C. Restricted combustion air
D. Correct burner alignment
Answer: C
Rationale: Insufficient combustion air can cause poor combustion and
elevated carbon monoxide production.
10. The best source for required installation clearances is:
A. A random internet forum
B. The manufacturer's installation instructions and applicable code
C. The thermostat manual
D. The homeowner's preferred settings
Answer: B
Rationale: Equipment-specific requirements and applicable codes establish
installation and clearance requirements.
11. A lockout/tagout procedure is designed to:
A. Increase furnace efficiency
B. Prevent unexpected energization during service
C. Increase gas pressure
D. Improve thermostat accuracy
Answer: B
Questions and Answers with
Rationales
Coverage: Gas Heating, Safety, Combustion, Furnaces, Controls, Venting,
Airflow, Installation, Service & Troubleshooting
SECTION 1 — SAFETY, CODES & SERVICE PRACTICES
1. Before servicing a gas furnace, the technician should first:
A. Increase the thermostat setting
B. Shut off the appropriate energy sources and follow safety procedures
C. Remove the blower assembly
D. Adjust the gas valve
Answer: B
Rationale: Gas and electrical energy must be controlled before service. Proper
lockout/tagout and manufacturer safety procedures reduce the risk of shock,
burns, fire, and unintended equipment operation.
2. The primary danger from incomplete combustion of natural gas is:
A. Oxygen enrichment
B. High humidity
C. Carbon monoxide production
D. Refrigerant migration
Answer: C
Rationale: Incomplete combustion can produce carbon monoxide (CO), a
colorless and potentially fatal gas.
,3. A technician should use a calibrated combustion analyzer primarily to:
A. Measure refrigerant pressure
B. Evaluate combustion and flue-gas characteristics
C. Measure blower RPM
D. Test capacitor capacitance
Answer: B
Rationale: A combustion analyzer measures parameters such as oxygen,
carbon monoxide, carbon dioxide, flue temperature, and efficiency-related
information.
4. If a strong gas odor is detected inside a building, the technician should:
A. Immediately operate electrical switches
B. Light a burner to locate the leak
C. Follow emergency gas-leak procedures and avoid ignition sources
D. Increase furnace airflow
Answer: C
Rationale: Gas accumulation can create an explosion hazard. Ignition sources,
including electrical switches and flames, should be avoided.
5. The purpose of a gas appliance sediment trap is to:
A. Increase manifold pressure
B. Collect debris or condensate before it enters the gas valve
C. Increase combustion temperature
D. Reduce blower noise
Answer: B
,Rationale: A sediment trap helps prevent contaminants from entering
sensitive gas-control components.
6. Which PPE is most appropriate when working around an operating gas
furnace?
A. Safety glasses and appropriate protective equipment
B. Sandals and cotton gloves only
C. No PPE because furnaces are low voltage
D. Hearing protection only
Answer: A
Rationale: Service work can involve electrical hazards, hot surfaces, sharp
metal, combustion gases, and moving components.
7. A technician should verify combustion safety after changing:
A. Thermostat batteries
B. Gas input, burner operation, or venting components
C. Filter size only
D. Condensate tubing color
Answer: B
Rationale: Changes affecting fuel input or combustion/venting can alter
combustion performance and safety.
8. Carbon monoxide detectors are intended to:
A. Replace proper furnace maintenance
B. Replace combustion testing
C. Provide an additional warning of dangerous CO levels
D. Control the gas valve
Answer: C
, Rationale: CO detectors provide supplemental protection but do not replace
proper appliance installation, maintenance, and combustion testing.
9. Which condition can contribute to incomplete combustion?
A. Proper combustion air
B. Correct gas pressure
C. Restricted combustion air
D. Correct burner alignment
Answer: C
Rationale: Insufficient combustion air can cause poor combustion and
elevated carbon monoxide production.
10. The best source for required installation clearances is:
A. A random internet forum
B. The manufacturer's installation instructions and applicable code
C. The thermostat manual
D. The homeowner's preferred settings
Answer: B
Rationale: Equipment-specific requirements and applicable codes establish
installation and clearance requirements.
11. A lockout/tagout procedure is designed to:
A. Increase furnace efficiency
B. Prevent unexpected energization during service
C. Increase gas pressure
D. Improve thermostat accuracy
Answer: B
