Gas Fitter Licensing Exam Practice Test
100 Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A Instant Download Pdf
1. Which gas is lighter than air and will rise if leaked?
A. Propane
B. Butane
C. Natural gas
D. Carbon monoxide
Rationale: Natural gas is primarily methane, which has a specific gravity of
approximately 0.55-0.6 and is lighter than air, causing it to rise and dissipate.
2. What is the primary purpose of a gas pressure regulator?
A. Increase gas pressure for appliance operation
B. Reduce and control gas pressure to a safe level
C. Filter impurities from the gas supply
D. Measure gas volume consumed
Rationale: Gas pressure regulators reduce incoming high-pressure gas from
the supply line to a safe, usable pressure for appliances and maintain
consistent downstream pressure.
3. Which type of piping is prohibited for interior gas lines in residential
buildings?
A. Black steel
B. Copper
C. PVC
D. CSST
Rationale: PVC is not approved for natural gas because it cannot withstand
gas system pressure, may degrade, and is not rated for flammable gas use.
,4. What is the correct thread sealant for natural gas piping?
A. Silicone caulk
B. Pipe dope for water only
C. Approved gas-rated pipe thread compound
D. Epoxy resin
Rationale: Only gas-rated compounds are suitable for threaded joints on gas
piping to prevent leaks and ensure safety with hydrocarbon exposure.
5. Which flame characteristic indicates complete combustion in a gas
appliance?
A. Yellow, sooty flame
B. Orange-tipped flame
C. Blue flame with minimal yellow tips
D. Red flame with lifting
Rationale: Blue flames indicate complete combustion with proper air-fuel
mixture, reducing carbon monoxide risk.
6. What is the primary hazard of carbon monoxide from gas appliances?
A. Skin irritation
B. Fire hazard
C. Asphyxiation
D. Rusting of appliances
Rationale: CO is odorless and colorless; it binds to hemoglobin more strongly
than oxygen, reducing oxygen delivery in the body and leading to poisoning.
7. Which component senses flame presence in a modern gas furnace?
A. Pressure switch
B. Vent damper
C. Flame rod/sensor
D. Gas valve
Rationale: Flame sensors provide feedback to ensure safe burner operation
and shut off gas if flame is lost.
8. What is the typical manifold pressure for natural gas appliances?
A. 1.0" WC
B. 3.5" WC
C. 7.0" WC
, D. 14.0" WC
Rationale: Most standard natural gas appliances operate at approximately
3.5 inches water column manifold pressure.
9. Flexible appliance connectors must not pass through:
A. Behind the appliance
B. Walls or floors
C. Service areas
D. Open spaces
Rationale: Flexible connectors can wear and should not be concealed through
walls or floors where they cannot be inspected.
10. What is the primary component of natural gas supplied to consumers?
A. Butane
B. Propane
C. Methane
D. Ethane
Rationale: Methane makes up approximately 90% or more of typical natural
gas supplies.
11. Propane is stored and transported in what state?
A. Vapor state only
B. Solid state
C. Liquid under pressure
D. Free gas in cylinders
Rationale: Propane is liquefied under pressure for efficient storage and
transportation.
12. Which gas is heavier than air?
A. Natural gas
B. Propane
C. Hydrogen
D. Nitrogen
Rationale: Propane has a specific gravity of approximately 1.52 and
accumulates near floors, requiring careful ventilation in enclosed spaces.
13. What is the primary purpose of venting a gas appliance?
A. Increase combustion efficiency
100 Questions And Correct Answers
(Verified Answers) Plus Rationales
2026 Q&A Instant Download Pdf
1. Which gas is lighter than air and will rise if leaked?
A. Propane
B. Butane
C. Natural gas
D. Carbon monoxide
Rationale: Natural gas is primarily methane, which has a specific gravity of
approximately 0.55-0.6 and is lighter than air, causing it to rise and dissipate.
2. What is the primary purpose of a gas pressure regulator?
A. Increase gas pressure for appliance operation
B. Reduce and control gas pressure to a safe level
C. Filter impurities from the gas supply
D. Measure gas volume consumed
Rationale: Gas pressure regulators reduce incoming high-pressure gas from
the supply line to a safe, usable pressure for appliances and maintain
consistent downstream pressure.
3. Which type of piping is prohibited for interior gas lines in residential
buildings?
A. Black steel
B. Copper
C. PVC
D. CSST
Rationale: PVC is not approved for natural gas because it cannot withstand
gas system pressure, may degrade, and is not rated for flammable gas use.
,4. What is the correct thread sealant for natural gas piping?
A. Silicone caulk
B. Pipe dope for water only
C. Approved gas-rated pipe thread compound
D. Epoxy resin
Rationale: Only gas-rated compounds are suitable for threaded joints on gas
piping to prevent leaks and ensure safety with hydrocarbon exposure.
5. Which flame characteristic indicates complete combustion in a gas
appliance?
A. Yellow, sooty flame
B. Orange-tipped flame
C. Blue flame with minimal yellow tips
D. Red flame with lifting
Rationale: Blue flames indicate complete combustion with proper air-fuel
mixture, reducing carbon monoxide risk.
6. What is the primary hazard of carbon monoxide from gas appliances?
A. Skin irritation
B. Fire hazard
C. Asphyxiation
D. Rusting of appliances
Rationale: CO is odorless and colorless; it binds to hemoglobin more strongly
than oxygen, reducing oxygen delivery in the body and leading to poisoning.
7. Which component senses flame presence in a modern gas furnace?
A. Pressure switch
B. Vent damper
C. Flame rod/sensor
D. Gas valve
Rationale: Flame sensors provide feedback to ensure safe burner operation
and shut off gas if flame is lost.
8. What is the typical manifold pressure for natural gas appliances?
A. 1.0" WC
B. 3.5" WC
C. 7.0" WC
, D. 14.0" WC
Rationale: Most standard natural gas appliances operate at approximately
3.5 inches water column manifold pressure.
9. Flexible appliance connectors must not pass through:
A. Behind the appliance
B. Walls or floors
C. Service areas
D. Open spaces
Rationale: Flexible connectors can wear and should not be concealed through
walls or floors where they cannot be inspected.
10. What is the primary component of natural gas supplied to consumers?
A. Butane
B. Propane
C. Methane
D. Ethane
Rationale: Methane makes up approximately 90% or more of typical natural
gas supplies.
11. Propane is stored and transported in what state?
A. Vapor state only
B. Solid state
C. Liquid under pressure
D. Free gas in cylinders
Rationale: Propane is liquefied under pressure for efficient storage and
transportation.
12. Which gas is heavier than air?
A. Natural gas
B. Propane
C. Hydrogen
D. Nitrogen
Rationale: Propane has a specific gravity of approximately 1.52 and
accumulates near floors, requiring careful ventilation in enclosed spaces.
13. What is the primary purpose of venting a gas appliance?
A. Increase combustion efficiency
