CO Gas Fitter Contractor Exam Questions
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
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1. Which type of gas is commonly classified as a fuel gas used in
residential and commercial piping systems?
A. Oxygen
B. Nitrogen
C. Natural gas
D. Carbon dioxide
Rationale: Natural gas is a commonly distributed fuel gas used for
appliances such as furnaces, boilers, water heaters, ranges, and
dryers. Oxygen and nitrogen are not fuel gases, while carbon dioxide
is a combustion product rather than a normal fuel supply.
2. What is the primary purpose of a gas piping system?
,A. To supply combustion air
B. To safely convey fuel gas to approved appliances
C. To remove combustion products
D. To provide electrical grounding
Rationale: Gas piping is designed to transport fuel gas from the source
to appliances where the gas is burned. Combustion air and flue gases
are handled by separate systems, and gas piping should not be used
as an electrical grounding system.
3. Which condition is most important when determining whether a
gas appliance can operate safely?
A. The appliance's paint color
B. The length of the building's electrical wiring
C. Adequate combustion air and proper venting
D. The number of windows in unrelated rooms
Rationale: Fuel-burning appliances require sufficient combustion air
and an appropriate method of venting combustion products.
Inadequate air or improper venting can result in incomplete
combustion and dangerous accumulation of combustion products.
4. What is the primary hazard associated with an uncontrolled
natural-gas leak?
,A. Freezing of the gas line
B. Corrosion of copper wiring
C. Fire or explosion
D. Excessive water pressure
Rationale: Escaped fuel gas can accumulate in an enclosed space and
form a combustible mixture with air. An ignition source can then
cause a fire or explosion.
5. Before installing or modifying gas piping, what should a contractor
determine first?
A. The appliance manufacturer's paint specification
B. The customer's preferred pipe color
C. Applicable codes, approved materials, and system requirements
D. The brand of electrical receptacles in the building
Rationale: Gas work must comply with the applicable fuel-gas
requirements, adopted codes, local requirements, and manufacturer
instructions. The contractor must establish the requirements before
selecting materials or beginning installation.
6. Which fitting is commonly used to change the direction of a gas
pipe by 90 degrees?
, A. Coupling
B. Elbow
C. Union
D. Bushing
Rationale: An elbow changes the direction of piping, commonly by 90
degrees or 45 degrees. A coupling joins pipe sections, a union provides
a disconnectable connection, and a bushing generally changes size or
thread configuration.
7. What is the main purpose of a union in a gas piping system?
A. To increase gas pressure
B. To filter the gas
C. To allow a piping section or appliance connection to be
disconnected
D. To provide combustion air
Rationale: A union permits convenient disconnection of piping without
rotating or removing long sections of pipe. This can be particularly
useful near appliances that may require servicing or replacement.
8. What is the purpose of a gas shutoff valve installed at an
appliance?
and Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf
1. Which type of gas is commonly classified as a fuel gas used in
residential and commercial piping systems?
A. Oxygen
B. Nitrogen
C. Natural gas
D. Carbon dioxide
Rationale: Natural gas is a commonly distributed fuel gas used for
appliances such as furnaces, boilers, water heaters, ranges, and
dryers. Oxygen and nitrogen are not fuel gases, while carbon dioxide
is a combustion product rather than a normal fuel supply.
2. What is the primary purpose of a gas piping system?
,A. To supply combustion air
B. To safely convey fuel gas to approved appliances
C. To remove combustion products
D. To provide electrical grounding
Rationale: Gas piping is designed to transport fuel gas from the source
to appliances where the gas is burned. Combustion air and flue gases
are handled by separate systems, and gas piping should not be used
as an electrical grounding system.
3. Which condition is most important when determining whether a
gas appliance can operate safely?
A. The appliance's paint color
B. The length of the building's electrical wiring
C. Adequate combustion air and proper venting
D. The number of windows in unrelated rooms
Rationale: Fuel-burning appliances require sufficient combustion air
and an appropriate method of venting combustion products.
Inadequate air or improper venting can result in incomplete
combustion and dangerous accumulation of combustion products.
4. What is the primary hazard associated with an uncontrolled
natural-gas leak?
,A. Freezing of the gas line
B. Corrosion of copper wiring
C. Fire or explosion
D. Excessive water pressure
Rationale: Escaped fuel gas can accumulate in an enclosed space and
form a combustible mixture with air. An ignition source can then
cause a fire or explosion.
5. Before installing or modifying gas piping, what should a contractor
determine first?
A. The appliance manufacturer's paint specification
B. The customer's preferred pipe color
C. Applicable codes, approved materials, and system requirements
D. The brand of electrical receptacles in the building
Rationale: Gas work must comply with the applicable fuel-gas
requirements, adopted codes, local requirements, and manufacturer
instructions. The contractor must establish the requirements before
selecting materials or beginning installation.
6. Which fitting is commonly used to change the direction of a gas
pipe by 90 degrees?
, A. Coupling
B. Elbow
C. Union
D. Bushing
Rationale: An elbow changes the direction of piping, commonly by 90
degrees or 45 degrees. A coupling joins pipe sections, a union provides
a disconnectable connection, and a bushing generally changes size or
thread configuration.
7. What is the main purpose of a union in a gas piping system?
A. To increase gas pressure
B. To filter the gas
C. To allow a piping section or appliance connection to be
disconnected
D. To provide combustion air
Rationale: A union permits convenient disconnection of piping without
rotating or removing long sections of pipe. This can be particularly
useful near appliances that may require servicing or replacement.
8. What is the purpose of a gas shutoff valve installed at an
appliance?
