NATE GAS HEATING CERTIFICATION EXAM Q&A | LATEST
VERSION 2027-2028 | ALL QUESTIONS AND ANSWERS PLUS
DETAILED RATIONALES | COMPLETE STUDYGUIDE|
GUARANTEED PASS | DOWNLOAD INSTANT PDF 2027-2028
1. A gas-fired furnace is operating, but the supply-air temperature remains well below the
expected range. The blower is running normally. Which condition should the technician
investigate first?
A. Incorrect thermostat anticipator setting
B. Restricted return airflow
C. Excessively high gas input
D. Open high-limit switch
Restricted return airflow can reduce the volume of air moving across the heat exchanger and
affect furnace performance. The technician should verify filters, return ducts, dampers, and
other airflow restrictions before making combustion adjustments.
2. Before servicing a gas furnace, which action provides the most appropriate initial safety
measure?
A. Increase the thermostat setting
B. Close the supply-air registers
C. De-energize the equipment and follow applicable gas and electrical safety procedures
D. Remove the burner assembly
The equipment should be safely de-energized and isolated as required before service. Gas-
fired equipment presents both electrical and combustion hazards.
3. A furnace has a standing pilot that repeatedly goes out after the burner operates. Which
component should receive particular attention?
A. Evaporator coil
B. Thermostat subbase
C. Condensate pump
D. Flame-sensing/pilot safety system
A pilot safety system is designed to prevent continued gas flow when flame is not proven.
Repeated pilot dropout requires inspection of flame quality, thermocouple or flame-proving
components, pilot assembly, and related controls.
4. What is the primary purpose of a furnace heat exchanger?
A. Transfer heat from combustion products to the circulating air while keeping the two air
streams separated
B. Increase gas pressure entering the manifold
,C. Regulate thermostat voltage
D. Remove moisture from return air
The heat exchanger transfers combustion heat to the air circulated through the conditioned
space while preventing combustion products from entering the occupied-air stream.
5. A technician measures manifold gas pressure that is significantly below the equipment
manufacturer's specified value. What is the best next step?
A. Increase the gas valve adjustment immediately
B. Verify inlet gas pressure and system conditions before adjusting the valve
C. Replace the thermostat
D. Increase blower speed
Low manifold pressure may result from inadequate inlet pressure, piping restrictions,
regulator problems, or other conditions. The technician should diagnose the cause before
adjusting the gas valve.
6. Which instrument is most appropriate for verifying gas pressure at a furnace?
A. Clamp ammeter
B. Psychrometer
C. Manometer
D. Megohmmeter
A manometer is commonly used to measure gas pressure accurately at the appliance and
manifold test points.
7. A furnace burner produces mostly yellow, unstable flames rather than a predominantly
blue flame pattern. What should the technician suspect?
A. Possible incomplete combustion or improper air-to-gas mixture
B. Excessive return-air volume only
C. Correct combustion with normal operation
D. A failed blower capacitor
Abnormal yellow or unstable flame characteristics can indicate improper combustion,
contamination, insufficient primary air, or other problems requiring investigation.
8. Which condition can cause a furnace rollout switch to trip?
A. Properly adjusted thermostat
B. Clean return-air filter
C. Correct manifold pressure
D. Combustion or venting problems causing flame rollout
Rollout protection responds to abnormal flame movement outside the intended combustion
area. Venting restrictions, blocked heat exchangers, improper combustion, or other serious
conditions may contribute.
,9. A technician finds that the furnace inducer operates, but the ignition sequence stops
before gas is energized. Which control should be evaluated?
A. Evaporator coil
B. Pressure switch
C. Condenser fan motor
D. Outdoor thermostat
The pressure switch verifies adequate venting or inducer-generated pressure before the
control permits the ignition sequence to proceed.
10. What is the primary purpose of a furnace high-limit control?
A. Increase gas flow during startup
B. Control outdoor humidity
C. Protect the furnace from excessive heat
D. Maintain pilot flame color
The high-limit control opens the heating circuit when temperatures exceed its designed limit,
helping protect the furnace and heat exchanger.
11. A homeowner reports that the furnace cycles on and off every few minutes. The air
filter is clean. Which condition should be investigated?
A. Oversized furnace or restricted airflow
B. Excessive outdoor humidity
C. Low cooling load
D. Dirty condenser coil
Short cycling can result from excessive furnace capacity, inadequate airflow, high-limit
operation, thermostat issues, or other control problems.
12. Which component initiates the ignition sequence in many modern induced-draft gas
furnaces?
A. Condenser fan
B. Evaporator fan relay
C. Humidifier valve
D. Integrated furnace control
The integrated furnace control coordinates the ignition sequence, blower operation, safety
checks, and other furnace functions in many modern systems.
13. A technician is checking a furnace that uses electronic ignition. Which condition must
generally be established before the gas valve is permitted to open?
A. The cooling thermostat must be energized
B. Required safety and ignition sequence conditions must be satisfied
C. The evaporator coil must be cold
D. The outdoor fan must be operating
, Modern ignition controls use a defined sequence involving safety checks, inducer operation,
ignition, and flame proving before allowing continued gas operation.
14. What is the purpose of a flame sensor on a modern gas furnace?
A. Measure supply-air temperature
B. Adjust blower speed
C. Confirm that burner flame has been established
D. Measure manifold pressure
The flame sensor provides proof of flame so the control can determine whether it is safe to
continue supplying gas.
15. A furnace ignites normally but shuts the gas valve off several seconds later. Which
problem is most likely?
A. The thermostat has too much cooling demand
B. The return grille is oversized
C. The blower wheel is painted
D. The control is not receiving adequate flame-proving signal
If ignition occurs but gas is shut off shortly afterward, inadequate flame proving is a common
possibility. The sensor, grounding, wiring, burner flame, and control should be evaluated.
16. Which measurement is most useful for evaluating furnace temperature rise?
A. Difference between return-air and supply-air temperatures
B. Difference between outdoor and indoor humidity
C. Gas-line voltage
D. Refrigerant pressure
Temperature rise is determined by measuring the difference between return-air and supply-
air temperatures and comparing it with the equipment specifications.
17. A furnace nameplate specifies an allowable temperature rise of 35°F to 65°F. The
technician measures 78°F. Which condition should be investigated?
A. Excessive cooling airflow
B. Insufficient airflow or excessive heat input
C. Low outdoor temperature
D. Oversized return grille
A temperature rise above the manufacturer's range can result from inadequate airflow,
excessive firing rate, or other conditions and should be corrected before continued operation.
18. Which condition commonly reduces furnace airflow?
A. Clean filter
B. Properly sized ductwork
VERSION 2027-2028 | ALL QUESTIONS AND ANSWERS PLUS
DETAILED RATIONALES | COMPLETE STUDYGUIDE|
GUARANTEED PASS | DOWNLOAD INSTANT PDF 2027-2028
1. A gas-fired furnace is operating, but the supply-air temperature remains well below the
expected range. The blower is running normally. Which condition should the technician
investigate first?
A. Incorrect thermostat anticipator setting
B. Restricted return airflow
C. Excessively high gas input
D. Open high-limit switch
Restricted return airflow can reduce the volume of air moving across the heat exchanger and
affect furnace performance. The technician should verify filters, return ducts, dampers, and
other airflow restrictions before making combustion adjustments.
2. Before servicing a gas furnace, which action provides the most appropriate initial safety
measure?
A. Increase the thermostat setting
B. Close the supply-air registers
C. De-energize the equipment and follow applicable gas and electrical safety procedures
D. Remove the burner assembly
The equipment should be safely de-energized and isolated as required before service. Gas-
fired equipment presents both electrical and combustion hazards.
3. A furnace has a standing pilot that repeatedly goes out after the burner operates. Which
component should receive particular attention?
A. Evaporator coil
B. Thermostat subbase
C. Condensate pump
D. Flame-sensing/pilot safety system
A pilot safety system is designed to prevent continued gas flow when flame is not proven.
Repeated pilot dropout requires inspection of flame quality, thermocouple or flame-proving
components, pilot assembly, and related controls.
4. What is the primary purpose of a furnace heat exchanger?
A. Transfer heat from combustion products to the circulating air while keeping the two air
streams separated
B. Increase gas pressure entering the manifold
,C. Regulate thermostat voltage
D. Remove moisture from return air
The heat exchanger transfers combustion heat to the air circulated through the conditioned
space while preventing combustion products from entering the occupied-air stream.
5. A technician measures manifold gas pressure that is significantly below the equipment
manufacturer's specified value. What is the best next step?
A. Increase the gas valve adjustment immediately
B. Verify inlet gas pressure and system conditions before adjusting the valve
C. Replace the thermostat
D. Increase blower speed
Low manifold pressure may result from inadequate inlet pressure, piping restrictions,
regulator problems, or other conditions. The technician should diagnose the cause before
adjusting the gas valve.
6. Which instrument is most appropriate for verifying gas pressure at a furnace?
A. Clamp ammeter
B. Psychrometer
C. Manometer
D. Megohmmeter
A manometer is commonly used to measure gas pressure accurately at the appliance and
manifold test points.
7. A furnace burner produces mostly yellow, unstable flames rather than a predominantly
blue flame pattern. What should the technician suspect?
A. Possible incomplete combustion or improper air-to-gas mixture
B. Excessive return-air volume only
C. Correct combustion with normal operation
D. A failed blower capacitor
Abnormal yellow or unstable flame characteristics can indicate improper combustion,
contamination, insufficient primary air, or other problems requiring investigation.
8. Which condition can cause a furnace rollout switch to trip?
A. Properly adjusted thermostat
B. Clean return-air filter
C. Correct manifold pressure
D. Combustion or venting problems causing flame rollout
Rollout protection responds to abnormal flame movement outside the intended combustion
area. Venting restrictions, blocked heat exchangers, improper combustion, or other serious
conditions may contribute.
,9. A technician finds that the furnace inducer operates, but the ignition sequence stops
before gas is energized. Which control should be evaluated?
A. Evaporator coil
B. Pressure switch
C. Condenser fan motor
D. Outdoor thermostat
The pressure switch verifies adequate venting or inducer-generated pressure before the
control permits the ignition sequence to proceed.
10. What is the primary purpose of a furnace high-limit control?
A. Increase gas flow during startup
B. Control outdoor humidity
C. Protect the furnace from excessive heat
D. Maintain pilot flame color
The high-limit control opens the heating circuit when temperatures exceed its designed limit,
helping protect the furnace and heat exchanger.
11. A homeowner reports that the furnace cycles on and off every few minutes. The air
filter is clean. Which condition should be investigated?
A. Oversized furnace or restricted airflow
B. Excessive outdoor humidity
C. Low cooling load
D. Dirty condenser coil
Short cycling can result from excessive furnace capacity, inadequate airflow, high-limit
operation, thermostat issues, or other control problems.
12. Which component initiates the ignition sequence in many modern induced-draft gas
furnaces?
A. Condenser fan
B. Evaporator fan relay
C. Humidifier valve
D. Integrated furnace control
The integrated furnace control coordinates the ignition sequence, blower operation, safety
checks, and other furnace functions in many modern systems.
13. A technician is checking a furnace that uses electronic ignition. Which condition must
generally be established before the gas valve is permitted to open?
A. The cooling thermostat must be energized
B. Required safety and ignition sequence conditions must be satisfied
C. The evaporator coil must be cold
D. The outdoor fan must be operating
, Modern ignition controls use a defined sequence involving safety checks, inducer operation,
ignition, and flame proving before allowing continued gas operation.
14. What is the purpose of a flame sensor on a modern gas furnace?
A. Measure supply-air temperature
B. Adjust blower speed
C. Confirm that burner flame has been established
D. Measure manifold pressure
The flame sensor provides proof of flame so the control can determine whether it is safe to
continue supplying gas.
15. A furnace ignites normally but shuts the gas valve off several seconds later. Which
problem is most likely?
A. The thermostat has too much cooling demand
B. The return grille is oversized
C. The blower wheel is painted
D. The control is not receiving adequate flame-proving signal
If ignition occurs but gas is shut off shortly afterward, inadequate flame proving is a common
possibility. The sensor, grounding, wiring, burner flame, and control should be evaluated.
16. Which measurement is most useful for evaluating furnace temperature rise?
A. Difference between return-air and supply-air temperatures
B. Difference between outdoor and indoor humidity
C. Gas-line voltage
D. Refrigerant pressure
Temperature rise is determined by measuring the difference between return-air and supply-
air temperatures and comparing it with the equipment specifications.
17. A furnace nameplate specifies an allowable temperature rise of 35°F to 65°F. The
technician measures 78°F. Which condition should be investigated?
A. Excessive cooling airflow
B. Insufficient airflow or excessive heat input
C. Low outdoor temperature
D. Oversized return grille
A temperature rise above the manufacturer's range can result from inadequate airflow,
excessive firing rate, or other conditions and should be corrected before continued operation.
18. Which condition commonly reduces furnace airflow?
A. Clean filter
B. Properly sized ductwork
