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NATE Gas Heating Installation (GS) Certification
Exam | Latest verified Questions and Detailed
Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the NATE Gas
Heating Installation (GS) certification exam, administered by North American
Technician Excellence. The questions reflect the exam’s emphasis on practical, on-the-
job scenarios that technicians with at least two years of field experience regularly
encounter when installing, maintaining, and servicing residential and light commercial
gas furnaces up to 400,000 BTU/h. Content is organized around the core Knowledge
Areas of Technician Expertise (KATEs), covering safety protocols, proper use of tools
and instruments, identification and function of system components, correct installation
practices for piping, venting, and duct connections, combustion and ventilation
requirements, and essential startup checks such as manifold pressure and
temperature rise adjustments. Each item reinforces the application of relevant codes,
manufacturer specifications, and industry-accepted procedures needed for a
successful installation.
QUESTION 1
When pressure-testing a new gas piping system that includes connected appliance gas
controls, what is the maximum allowable air test pressure?
A. 15 psig
B. 10 psig
C. ½ psig (14 in. w.c.)
D. 3 psig
CORRECT ANSWER: C
EXPERT RATIONALE: NFPA 54 limits test pressure to ½ psig to prevent damage to gas
controls; higher pressures require the controls to be isolated.
,2|Page
QUESTION 2
A technician needs to measure the manifold gas pressure on an operating furnace.
Which instrument should be used?
A. Multimeter
B. Manometer
C. Combustion analyzer
D. Anemometer
CORRECT ANSWER: B
EXPERT RATIONALE: A manometer measures gas pressure in inches of water column; a
multimeter measures electrical values, while a combustion analyzer checks flue gases.
QUESTION 3
A natural gas furnace has a rating plate manifold pressure of 3.5 in. w.c. After adjusting
the gas valve, the technician reads 3.2 in. w.c. on the manometer. The furnace is
operating with acceptable combustion. What should the technician do?
A. Replace the gas valve immediately
B. Leave the adjustment as is because 3.2 in. w.c. is within tolerance
C. Increase the regulator setting to achieve exactly 3.5 in. w.c.
D. Convert the furnace to LP gas
CORRECT ANSWER: B
EXPERT RATIONALE: A deviation of ±0.3 in. w.c. is generally acceptable; 3.2 in. w.c. is
within the typical tolerance for proper combustion.
QUESTION 4
A standing pilot furnace is experiencing intermittent pilot outages. The thermocouple is
new. Which measurement would confirm a faulty safety magnet in the gas valve?
A. Open circuit thermocouple voltage below 17 mV
,3|Page
B. Closed circuit thermocouple voltage holding below 8 mV while the pilot is lit
C. Pilot flame lifting off the thermocouple tip
D. 24 VAC present at the gas valve
CORRECT ANSWER: B
EXPERT RATIONALE: A healthy thermocouple should maintain at least 8–12 mV closed
circuit; a lower reading under load with a clean pilot suggests the magnet coil is
dropping out.
QUESTION 5
A technician notices the rollout switch on a gas furnace has tripped and requires manual
reset. This switch most likely protects against:
A. Excessive flue gas temperature
B. Blocked return air
C. Flame rolling out of the combustion chamber due to a blocked heat exchanger or
vent
D. Low gas pressure
CORRECT ANSWER: C
EXPERT RATIONALE: Rollout switches are mounted near the burner opening and trip if
flame escapes the combustion chamber, typically due to heat exchanger failure or
severe venting problems.
QUESTION 6
When installing a Category I natural draft furnace, the required minimum upward slope
of the horizontal vent connector is:
A. ⅛ inch per foot
B. ¼ inch per foot
C. ½ inch per foot
, 4|Page
D. Level, no slope required
CORRECT ANSWER: B
EXPERT RATIONALE: NFPA 54/NFGC requires a ¼ inch per foot upward slope to allow
proper draft and condensate drainage in Category I vent connectors.
QUESTION 7
A condensing furnace produces acidic condensate. Where local codes permit, what
should be done before discharging into a floor drain?
A. Increase the condensate trap size
B. Neutralize the condensate with a limestone chip neutralizer
C. Dilute with fresh water only
D. Route directly to the sanitary sewer without treatment
CORRECT ANSWER: B
EXPERT RATIONALE: Condensate pH ranges from 3–5; a neutralizer cartridge raises pH
to reduce corrosion in drains and comply with plumbing codes.
QUESTION 8
What is the primary purpose of the inducer motor in a mid-efficiency (80%) furnace?
A. To push combustion air into the burner
B. To draw flue gases through the heat exchanger and vent them outside
C. To circulate room air through the furnace
D. To cool the electronic controls
CORRECT ANSWER: B
EXPERT RATIONALE: An inducer creates negative pressure in the heat exchanger to
purge flue gases and maintain proper draft, especially in induced-draft furnaces.
NATE Gas Heating Installation (GS) Certification
Exam | Latest verified Questions and Detailed
Answers
OVERVIEW DESCRIPTION
This comprehensive set of multiple choice questions is designed for the NATE Gas
Heating Installation (GS) certification exam, administered by North American
Technician Excellence. The questions reflect the exam’s emphasis on practical, on-the-
job scenarios that technicians with at least two years of field experience regularly
encounter when installing, maintaining, and servicing residential and light commercial
gas furnaces up to 400,000 BTU/h. Content is organized around the core Knowledge
Areas of Technician Expertise (KATEs), covering safety protocols, proper use of tools
and instruments, identification and function of system components, correct installation
practices for piping, venting, and duct connections, combustion and ventilation
requirements, and essential startup checks such as manifold pressure and
temperature rise adjustments. Each item reinforces the application of relevant codes,
manufacturer specifications, and industry-accepted procedures needed for a
successful installation.
QUESTION 1
When pressure-testing a new gas piping system that includes connected appliance gas
controls, what is the maximum allowable air test pressure?
A. 15 psig
B. 10 psig
C. ½ psig (14 in. w.c.)
D. 3 psig
CORRECT ANSWER: C
EXPERT RATIONALE: NFPA 54 limits test pressure to ½ psig to prevent damage to gas
controls; higher pressures require the controls to be isolated.
,2|Page
QUESTION 2
A technician needs to measure the manifold gas pressure on an operating furnace.
Which instrument should be used?
A. Multimeter
B. Manometer
C. Combustion analyzer
D. Anemometer
CORRECT ANSWER: B
EXPERT RATIONALE: A manometer measures gas pressure in inches of water column; a
multimeter measures electrical values, while a combustion analyzer checks flue gases.
QUESTION 3
A natural gas furnace has a rating plate manifold pressure of 3.5 in. w.c. After adjusting
the gas valve, the technician reads 3.2 in. w.c. on the manometer. The furnace is
operating with acceptable combustion. What should the technician do?
A. Replace the gas valve immediately
B. Leave the adjustment as is because 3.2 in. w.c. is within tolerance
C. Increase the regulator setting to achieve exactly 3.5 in. w.c.
D. Convert the furnace to LP gas
CORRECT ANSWER: B
EXPERT RATIONALE: A deviation of ±0.3 in. w.c. is generally acceptable; 3.2 in. w.c. is
within the typical tolerance for proper combustion.
QUESTION 4
A standing pilot furnace is experiencing intermittent pilot outages. The thermocouple is
new. Which measurement would confirm a faulty safety magnet in the gas valve?
A. Open circuit thermocouple voltage below 17 mV
,3|Page
B. Closed circuit thermocouple voltage holding below 8 mV while the pilot is lit
C. Pilot flame lifting off the thermocouple tip
D. 24 VAC present at the gas valve
CORRECT ANSWER: B
EXPERT RATIONALE: A healthy thermocouple should maintain at least 8–12 mV closed
circuit; a lower reading under load with a clean pilot suggests the magnet coil is
dropping out.
QUESTION 5
A technician notices the rollout switch on a gas furnace has tripped and requires manual
reset. This switch most likely protects against:
A. Excessive flue gas temperature
B. Blocked return air
C. Flame rolling out of the combustion chamber due to a blocked heat exchanger or
vent
D. Low gas pressure
CORRECT ANSWER: C
EXPERT RATIONALE: Rollout switches are mounted near the burner opening and trip if
flame escapes the combustion chamber, typically due to heat exchanger failure or
severe venting problems.
QUESTION 6
When installing a Category I natural draft furnace, the required minimum upward slope
of the horizontal vent connector is:
A. ⅛ inch per foot
B. ¼ inch per foot
C. ½ inch per foot
, 4|Page
D. Level, no slope required
CORRECT ANSWER: B
EXPERT RATIONALE: NFPA 54/NFGC requires a ¼ inch per foot upward slope to allow
proper draft and condensate drainage in Category I vent connectors.
QUESTION 7
A condensing furnace produces acidic condensate. Where local codes permit, what
should be done before discharging into a floor drain?
A. Increase the condensate trap size
B. Neutralize the condensate with a limestone chip neutralizer
C. Dilute with fresh water only
D. Route directly to the sanitary sewer without treatment
CORRECT ANSWER: B
EXPERT RATIONALE: Condensate pH ranges from 3–5; a neutralizer cartridge raises pH
to reduce corrosion in drains and comply with plumbing codes.
QUESTION 8
What is the primary purpose of the inducer motor in a mid-efficiency (80%) furnace?
A. To push combustion air into the burner
B. To draw flue gases through the heat exchanger and vent them outside
C. To circulate room air through the furnace
D. To cool the electronic controls
CORRECT ANSWER: B
EXPERT RATIONALE: An inducer creates negative pressure in the heat exchanger to
purge flue gases and maintain proper draft, especially in induced-draft furnaces.
