1|Page
NATE GAS HEATING NEWEST EXAM
2026 | 150 QUESTIONS AND CORRECT
DETAILED ANSWERS WITH
RATIONALE |RATED A+ |REVISED!!
1. A technician measures 24 VAC at the thermostat R and C
terminals but the furnace does not initiate a call for heat. What is
the MOST likely cause?
A. Failed transformer
B. Open thermostat contacts
C. Gas valve failure
D. Cracked heat exchanger
The presence of 24 VAC confirms transformer operation; an
open thermostat prevents the control board from receiving a heat
call.
2. Which gas law best explains pressure changes in a sealed
combustion chamber as temperature increases?
A. Dalton’s Law
B. Gay-Lussac’s Law
C. Boyle’s Law
D. Charles’ Law
Gay-Lussac’s Law states that pressure is directly proportional to
temperature at constant volume.
3. A furnace repeatedly locks out due to flame failure. Which
diagnostic step should be performed FIRST?
A. Replace the ignition control module
B. Increase manifold gas pressure
C. Verify flame sensor microamp signal
D. Replace the gas valve
,2|Page
Confirming flame rectification signal prevents unnecessary
component replacement.
4. What is the PRIMARY safety function of a high-limit switch?
A. Control blower delay
B. Regulate gas pressure
C. Shut down burners during overheating
D. Prove inducer operation
High-limit switches protect the heat exchanger and structure
from excessive temperatures.
5. A technician measures 3.2 in. w.c. manifold pressure on a natural
gas furnace rated for 3.5 in. w.c. What is the BEST action?
A. No action required
B. Replace the gas valve
C. Adjust the regulator to specification
D. Increase thermostat setpoint
Manifold pressure must match manufacturer specifications for
proper combustion.
6. Which component proves draft before ignition on an induced-draft
furnace?
A. Flame sensor
B. Limit switch
C. Pressure switch
D. Rollout switch
The pressure switch confirms inducer operation and proper
venting.
7. A rollout switch trips repeatedly. What condition is MOST likely
present?
A. Dirty air filter
B. Weak flame signal
C. Blocked heat exchanger or vent
D. Faulty thermostat
Flame rollout indicates combustion gases escaping the burner
area.
8. When clocking a gas meter, what measurement is used to
determine input rate?
,3|Page
A. Inches of water column
B. Voltage drop
C. Cubic feet per hour
D. BTUs per minute
Gas input is calculated using cubic feet consumed over time.
9. Which ignition system uses a silicon nitride element?
A. Standing pilot
B. Spark ignition
C. Hot surface ignition
D. Intermittent pilot
Hot surface igniters are typically made of silicon nitride or
carbide.
10. Excessive CO production is MOST commonly caused by:
A. High static pressure
B. Oversized blower motor
C. Incomplete combustion
D. Faulty thermostat
Incomplete combustion leads to carbon monoxide formation.
11. A furnace short cycles on the high limit. Which condition
should be checked FIRST?
A. Gas orifice size
B. Airflow restrictions
C. Flame sensor alignment
D. Line voltage polarity
Restricted airflow causes overheating and limit trips.
12. What is the MINIMUM recommended combustion air source
for a confined space furnace room?
A. Return duct leakage
B. Attic infiltration
C. Dedicated combustion air openings
D. Open blower compartment
Codes require permanent combustion air provisions.
13. A cracked heat exchanger is MOST likely to cause which
symptom?
A. Low manifold pressure
, 4|Page
B. Delayed ignition
C. Flame disturbance when blower starts
D. Inadequate inducer airflow
Blower operation can disrupt flames if cracks allow air intrusion.
14. Which meter is required to measure flame rectification?
A. Clamp-on ammeter
B. Ohmmeter
C. Microamp meter in series
D. Voltmeter in parallel
Flame rectification is measured in microamps DC.
15. The purpose of an inducer post-purge is to:
A. Increase ignition temperature
B. Reduce gas pressure
C. Clear residual combustion gases
D. Improve flame sensing
Post-purge enhances safety and venting.
16. A technician observes yellow, lazy flames. What is the
MOST likely cause?
A. Excess combustion air
B. High manifold pressure
C. Dirty burners or insufficient primary air
D. Faulty pressure switch
Proper air-fuel mixing produces sharp blue flames.
17. Which code governs residential fuel gas installations in most
U.S. jurisdictions?
A. NEC
B. IFGC
C. IMC
D. NFPA 99
The International Fuel Gas Code is widely adopted.
18. A pressure switch hose is found full of water. What system
design issue is indicated?
A. Oversized inducer
B. Improper condensate drainage
C. Faulty pressure switch
NATE GAS HEATING NEWEST EXAM
2026 | 150 QUESTIONS AND CORRECT
DETAILED ANSWERS WITH
RATIONALE |RATED A+ |REVISED!!
1. A technician measures 24 VAC at the thermostat R and C
terminals but the furnace does not initiate a call for heat. What is
the MOST likely cause?
A. Failed transformer
B. Open thermostat contacts
C. Gas valve failure
D. Cracked heat exchanger
The presence of 24 VAC confirms transformer operation; an
open thermostat prevents the control board from receiving a heat
call.
2. Which gas law best explains pressure changes in a sealed
combustion chamber as temperature increases?
A. Dalton’s Law
B. Gay-Lussac’s Law
C. Boyle’s Law
D. Charles’ Law
Gay-Lussac’s Law states that pressure is directly proportional to
temperature at constant volume.
3. A furnace repeatedly locks out due to flame failure. Which
diagnostic step should be performed FIRST?
A. Replace the ignition control module
B. Increase manifold gas pressure
C. Verify flame sensor microamp signal
D. Replace the gas valve
,2|Page
Confirming flame rectification signal prevents unnecessary
component replacement.
4. What is the PRIMARY safety function of a high-limit switch?
A. Control blower delay
B. Regulate gas pressure
C. Shut down burners during overheating
D. Prove inducer operation
High-limit switches protect the heat exchanger and structure
from excessive temperatures.
5. A technician measures 3.2 in. w.c. manifold pressure on a natural
gas furnace rated for 3.5 in. w.c. What is the BEST action?
A. No action required
B. Replace the gas valve
C. Adjust the regulator to specification
D. Increase thermostat setpoint
Manifold pressure must match manufacturer specifications for
proper combustion.
6. Which component proves draft before ignition on an induced-draft
furnace?
A. Flame sensor
B. Limit switch
C. Pressure switch
D. Rollout switch
The pressure switch confirms inducer operation and proper
venting.
7. A rollout switch trips repeatedly. What condition is MOST likely
present?
A. Dirty air filter
B. Weak flame signal
C. Blocked heat exchanger or vent
D. Faulty thermostat
Flame rollout indicates combustion gases escaping the burner
area.
8. When clocking a gas meter, what measurement is used to
determine input rate?
,3|Page
A. Inches of water column
B. Voltage drop
C. Cubic feet per hour
D. BTUs per minute
Gas input is calculated using cubic feet consumed over time.
9. Which ignition system uses a silicon nitride element?
A. Standing pilot
B. Spark ignition
C. Hot surface ignition
D. Intermittent pilot
Hot surface igniters are typically made of silicon nitride or
carbide.
10. Excessive CO production is MOST commonly caused by:
A. High static pressure
B. Oversized blower motor
C. Incomplete combustion
D. Faulty thermostat
Incomplete combustion leads to carbon monoxide formation.
11. A furnace short cycles on the high limit. Which condition
should be checked FIRST?
A. Gas orifice size
B. Airflow restrictions
C. Flame sensor alignment
D. Line voltage polarity
Restricted airflow causes overheating and limit trips.
12. What is the MINIMUM recommended combustion air source
for a confined space furnace room?
A. Return duct leakage
B. Attic infiltration
C. Dedicated combustion air openings
D. Open blower compartment
Codes require permanent combustion air provisions.
13. A cracked heat exchanger is MOST likely to cause which
symptom?
A. Low manifold pressure
, 4|Page
B. Delayed ignition
C. Flame disturbance when blower starts
D. Inadequate inducer airflow
Blower operation can disrupt flames if cracks allow air intrusion.
14. Which meter is required to measure flame rectification?
A. Clamp-on ammeter
B. Ohmmeter
C. Microamp meter in series
D. Voltmeter in parallel
Flame rectification is measured in microamps DC.
15. The purpose of an inducer post-purge is to:
A. Increase ignition temperature
B. Reduce gas pressure
C. Clear residual combustion gases
D. Improve flame sensing
Post-purge enhances safety and venting.
16. A technician observes yellow, lazy flames. What is the
MOST likely cause?
A. Excess combustion air
B. High manifold pressure
C. Dirty burners or insufficient primary air
D. Faulty pressure switch
Proper air-fuel mixing produces sharp blue flames.
17. Which code governs residential fuel gas installations in most
U.S. jurisdictions?
A. NEC
B. IFGC
C. IMC
D. NFPA 99
The International Fuel Gas Code is widely adopted.
18. A pressure switch hose is found full of water. What system
design issue is indicated?
A. Oversized inducer
B. Improper condensate drainage
C. Faulty pressure switch
