CO Mechanical Contractor Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A| Instant Download Pdf
1. Which type of piping material is commonly used for domestic hot
water systems?
A. PVC
B. Copper
C. Galvanized steel
D. Cast iron
Copper is preferred for domestic hot water due to its durability and
resistance to corrosion.
2. The minimum slope for a horizontal drain line is:
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
A slope of 1/4 inch per foot ensures proper drainage and prevents
standing water.
3. In HVAC systems, what does the term “ton” refer to?
A. The amount of heat required to melt 1 ton of ice in 24 hours
B. The weight of refrigerant
C. The airflow rate
D. Pipe diameter
A “ton” in HVAC measures cooling capacity, based on the energy to
melt 1 ton of ice per day.
4. The primary purpose of an expansion tank in a closed-loop hydronic
system is to:
A. Filter impurities
B. Heat water
, C. Absorb pressure changes due to thermal expansion
D. Circulate water
The expansion tank prevents excessive pressure in the system as
water heats and expands.
5. The recommended minimum clearance between a gas appliance and
combustible materials is:
A. 1 inch
B. 2 inches
C. 6 inches
D. 12 inches
Most gas appliance codes require a minimum of 6 inches clearance
for safety.
6. Which type of valve is typically used for throttling flow in a
mechanical system?
A. Gate valve
B. Globe valve
C. Ball valve
D. Check valve
Globe valves allow precise control of flow, making them ideal for
throttling applications.
7. What is the primary function of a check valve?
A. Regulate pressure
B. Prevent backflow
C. Control temperature
D. Reduce noise
Check valves allow flow in one direction only, preventing reverse flow
in the system.
8. In a fire sprinkler system, the water supply must be capable of:
A. 25% of system demand
B. 50% of system demand
C. 100% of system demand
D. 150% of system demand
Fire protection codes require the water supply to meet 100% of the
sprinkler system’s hydraulic demand.
9. Which of the following is an advantage of using PEX tubing in
plumbing systems?
A. Cannot withstand heat
, B. Requires soldering
C. Flexible and resistant to corrosion
D. Heavy and rigid
PEX is lightweight, flexible, and resistant to corrosion, making it
easier to install than rigid piping.
10. When sizing a mechanical system, which factor is most
important?
A. Pipe color
B. Load requirements
C. Material cost
D. Contractor preference
Proper sizing ensures the system can meet demand efficiently without
overloading components.
11. Which refrigerant is commonly used in modern HVAC systems
due to low ozone depletion potential?
A. R-22
B. R-410A
C. R-12
D. R-134a
R-410A is widely used as an environmentally safer alternative to
older refrigerants like R-22.
12. In a hydronic heating system, what is the function of a circulator
pump?
A. Heat the water
B. Move water through the system
C. Filter impurities
D. Drain the system
Circulator pumps maintain flow through radiators, baseboards, and
piping in hydronic systems.
13. What type of insulation is commonly used on refrigerant lines to
prevent condensation?
A. Fiberglass
B. Foam rubber
C. Mineral wool
D. Plastic wrap
Foam rubber insulation prevents condensation and energy loss on
refrigerant lines.
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A| Instant Download Pdf
1. Which type of piping material is commonly used for domestic hot
water systems?
A. PVC
B. Copper
C. Galvanized steel
D. Cast iron
Copper is preferred for domestic hot water due to its durability and
resistance to corrosion.
2. The minimum slope for a horizontal drain line is:
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
A slope of 1/4 inch per foot ensures proper drainage and prevents
standing water.
3. In HVAC systems, what does the term “ton” refer to?
A. The amount of heat required to melt 1 ton of ice in 24 hours
B. The weight of refrigerant
C. The airflow rate
D. Pipe diameter
A “ton” in HVAC measures cooling capacity, based on the energy to
melt 1 ton of ice per day.
4. The primary purpose of an expansion tank in a closed-loop hydronic
system is to:
A. Filter impurities
B. Heat water
, C. Absorb pressure changes due to thermal expansion
D. Circulate water
The expansion tank prevents excessive pressure in the system as
water heats and expands.
5. The recommended minimum clearance between a gas appliance and
combustible materials is:
A. 1 inch
B. 2 inches
C. 6 inches
D. 12 inches
Most gas appliance codes require a minimum of 6 inches clearance
for safety.
6. Which type of valve is typically used for throttling flow in a
mechanical system?
A. Gate valve
B. Globe valve
C. Ball valve
D. Check valve
Globe valves allow precise control of flow, making them ideal for
throttling applications.
7. What is the primary function of a check valve?
A. Regulate pressure
B. Prevent backflow
C. Control temperature
D. Reduce noise
Check valves allow flow in one direction only, preventing reverse flow
in the system.
8. In a fire sprinkler system, the water supply must be capable of:
A. 25% of system demand
B. 50% of system demand
C. 100% of system demand
D. 150% of system demand
Fire protection codes require the water supply to meet 100% of the
sprinkler system’s hydraulic demand.
9. Which of the following is an advantage of using PEX tubing in
plumbing systems?
A. Cannot withstand heat
, B. Requires soldering
C. Flexible and resistant to corrosion
D. Heavy and rigid
PEX is lightweight, flexible, and resistant to corrosion, making it
easier to install than rigid piping.
10. When sizing a mechanical system, which factor is most
important?
A. Pipe color
B. Load requirements
C. Material cost
D. Contractor preference
Proper sizing ensures the system can meet demand efficiently without
overloading components.
11. Which refrigerant is commonly used in modern HVAC systems
due to low ozone depletion potential?
A. R-22
B. R-410A
C. R-12
D. R-134a
R-410A is widely used as an environmentally safer alternative to
older refrigerants like R-22.
12. In a hydronic heating system, what is the function of a circulator
pump?
A. Heat the water
B. Move water through the system
C. Filter impurities
D. Drain the system
Circulator pumps maintain flow through radiators, baseboards, and
piping in hydronic systems.
13. What type of insulation is commonly used on refrigerant lines to
prevent condensation?
A. Fiberglass
B. Foam rubber
C. Mineral wool
D. Plastic wrap
Foam rubber insulation prevents condensation and energy loss on
refrigerant lines.
