NYC CUSTODIAN ENGINEER EXAM 200-
QUESTION MASTER STUDY GUIDE &
TECHNICAL RATIONALE (2026 EDITION)
NYC Custodian Engineer Civil Service Exam: Comprehensive
Phase I
1. According to the New York City Mechanical Code, what is the
maximum allowable pressure for a boiler to be legally classified
and operated as a "low-pressure" steam boiler?
• A. 5 psi
• B. 15 psi
• C. 100 psi
• D. 150 psi
• Rationale: In NYC, any steam boiler operating above 15 psi
is classified as high-pressure and requires a different class
of licensure and stricter operating protocols.
2. What is the primary function of the "Hartford Loop" in a steam
heating system found in many older New York City public school
buildings?
• A. To increase the velocity of steam as it travels to the
furthest radiator.
• B. To provide a bypass route for steam when the main header
is closed.
• C. To prevent the boiler from losing its water level
below a safe point in the event of a leak in the return
line.
• D. To trap air and vent it out of the system before it reaches
the boiler.
• Rationale: The Hartford Loop is a safety piping
arrangement that prevents water from being siphoned out
of the boiler if a return line breaks, protecting the crown
sheet from overheating.
,3. If a Custodian Engineer observes "priming" or "foaming" in the
boiler sight glass, which of the following is the most likely cause
and appropriate chemical treatment?
• A. Low water level; add more feedwater immediately.
• B. High concentration of dissolved solids or oil in
the water; perform a surface blowdown.
• C. Excessive oxygen in the system; add sodium sulfite.
• D. Scale buildup on the tubes; increase the dosage of
phosphates.
• Rationale: Foaming is caused by impurities on the surface
of the water; a surface blowdown removes these impurities
to prevent water carryover into the steam lines.
4. Which specific device is mandated by NYC code to shut off the fuel
supply to the burner if the water level in the boiler drops below the
lowest safe operating point?
• A. The pressuretrol
• B. The aqua-stat
• C. The low-water cutoff
• D. The OS&Y valve
• Rationale: The low-water cutoff is the most critical safety
device on a boiler, preventing a dry-fire condition which
could lead to a catastrophic boiler explosion.
5. In a centrifugal pump used for chilled water circulation, what is the
purpose of the "wear rings"?
• A. To provide a seal that prevents water from leaking out of
the pump shaft.
• B. To provide a replaceable surface that maintains
internal efficiency by minimizing leakage between
the discharge and suction sides.
• C. To hold the impeller in place on the pump shaft.
• D. To lubricate the bearings during high-speed operation.
, • Rationale: Wear rings allow the pump to maintain high
pressure by sealing the gap between the rotating impeller
and the stationary housing; they are designed to be
replaced as they wear down.
6. When managing a custodial staff under Local 891 or Local 94
contracts, what is the correct procedure for documentation when
an employee is injured on the job?
• A. Wait 48 hours to see if the injury improves before filing
paperwork.
• B. Call the Principal and ask for verbal permission to send
the employee home.
• C. Immediately ensure the employee receives
medical attention and file a Comprehensive
Accident Report (CA-1/CA-2) within the required
timeframe.
• D. Record the injury only in the school's unofficial daily
logbook.
• Rationale: Official NYC reporting ensures that the employee
is covered under Workers' Compensation and that the city is
protected from liability through proper documentation.
7. What does the term "Saturated Steam" refer to in a standard
heating boiler's operation?
• A. Steam that is at the same temperature and
pressure as the water from which it was evaporated.
• B. Steam that has been heated to a temperature higher than
its boiling point.
• C. Steam that contains a high percentage of liquid water
droplets.
• D. Steam that has passed through a superheater to increase
its energy.
• Rationale: Saturated steam exists in equilibrium with water
at a specific boiling point; most NYC heating systems use
saturated steam for efficient heat transfer.
, 8. Which grade of fuel oil is most commonly used in large NYC school
boilers that require pre-heating before the oil can be atomized and
burned?
• A. No. 2 Fuel Oil
• B. No. 4 Fuel Oil
• C. No. 6 Fuel Oil
• D. Kerosene
• Rationale: No. 6 oil is a heavy, residual oil that is thick at
room temperature and must be heated to lower its viscosity
for proper combustion in large industrial boilers.
9. A "Tri-Cock" or "Try-Cock" set on a large boiler is used for what
specific purpose?
• A. To blow down the water column to clear debris.
• B. To test the high-pressure alarm system.
• C. To manually verify the water level in the boiler if
the gauge glass is broken or unreliable.
• D. To inject chemicals directly into the steam drum.
• Rationale: Try-cocks are the secondary, manual method of
checking water level; steam from the top, water from the
bottom, and a mixture from the middle cock indicate a
proper level.
10. In a centralized HVAC system, what is the function of the
"Economizer" cycle?
• A. It reduces the speed of the fans to save electricity during
the night.
• B. It uses cool outdoor air to provide "free cooling"
for the building when the outdoor temperature is
lower than the indoor air temperature.
• C. It recycles used air to save on heating costs during the
winter.
• D. It shuts down the chiller when the building is unoccupied.
QUESTION MASTER STUDY GUIDE &
TECHNICAL RATIONALE (2026 EDITION)
NYC Custodian Engineer Civil Service Exam: Comprehensive
Phase I
1. According to the New York City Mechanical Code, what is the
maximum allowable pressure for a boiler to be legally classified
and operated as a "low-pressure" steam boiler?
• A. 5 psi
• B. 15 psi
• C. 100 psi
• D. 150 psi
• Rationale: In NYC, any steam boiler operating above 15 psi
is classified as high-pressure and requires a different class
of licensure and stricter operating protocols.
2. What is the primary function of the "Hartford Loop" in a steam
heating system found in many older New York City public school
buildings?
• A. To increase the velocity of steam as it travels to the
furthest radiator.
• B. To provide a bypass route for steam when the main header
is closed.
• C. To prevent the boiler from losing its water level
below a safe point in the event of a leak in the return
line.
• D. To trap air and vent it out of the system before it reaches
the boiler.
• Rationale: The Hartford Loop is a safety piping
arrangement that prevents water from being siphoned out
of the boiler if a return line breaks, protecting the crown
sheet from overheating.
,3. If a Custodian Engineer observes "priming" or "foaming" in the
boiler sight glass, which of the following is the most likely cause
and appropriate chemical treatment?
• A. Low water level; add more feedwater immediately.
• B. High concentration of dissolved solids or oil in
the water; perform a surface blowdown.
• C. Excessive oxygen in the system; add sodium sulfite.
• D. Scale buildup on the tubes; increase the dosage of
phosphates.
• Rationale: Foaming is caused by impurities on the surface
of the water; a surface blowdown removes these impurities
to prevent water carryover into the steam lines.
4. Which specific device is mandated by NYC code to shut off the fuel
supply to the burner if the water level in the boiler drops below the
lowest safe operating point?
• A. The pressuretrol
• B. The aqua-stat
• C. The low-water cutoff
• D. The OS&Y valve
• Rationale: The low-water cutoff is the most critical safety
device on a boiler, preventing a dry-fire condition which
could lead to a catastrophic boiler explosion.
5. In a centrifugal pump used for chilled water circulation, what is the
purpose of the "wear rings"?
• A. To provide a seal that prevents water from leaking out of
the pump shaft.
• B. To provide a replaceable surface that maintains
internal efficiency by minimizing leakage between
the discharge and suction sides.
• C. To hold the impeller in place on the pump shaft.
• D. To lubricate the bearings during high-speed operation.
, • Rationale: Wear rings allow the pump to maintain high
pressure by sealing the gap between the rotating impeller
and the stationary housing; they are designed to be
replaced as they wear down.
6. When managing a custodial staff under Local 891 or Local 94
contracts, what is the correct procedure for documentation when
an employee is injured on the job?
• A. Wait 48 hours to see if the injury improves before filing
paperwork.
• B. Call the Principal and ask for verbal permission to send
the employee home.
• C. Immediately ensure the employee receives
medical attention and file a Comprehensive
Accident Report (CA-1/CA-2) within the required
timeframe.
• D. Record the injury only in the school's unofficial daily
logbook.
• Rationale: Official NYC reporting ensures that the employee
is covered under Workers' Compensation and that the city is
protected from liability through proper documentation.
7. What does the term "Saturated Steam" refer to in a standard
heating boiler's operation?
• A. Steam that is at the same temperature and
pressure as the water from which it was evaporated.
• B. Steam that has been heated to a temperature higher than
its boiling point.
• C. Steam that contains a high percentage of liquid water
droplets.
• D. Steam that has passed through a superheater to increase
its energy.
• Rationale: Saturated steam exists in equilibrium with water
at a specific boiling point; most NYC heating systems use
saturated steam for efficient heat transfer.
, 8. Which grade of fuel oil is most commonly used in large NYC school
boilers that require pre-heating before the oil can be atomized and
burned?
• A. No. 2 Fuel Oil
• B. No. 4 Fuel Oil
• C. No. 6 Fuel Oil
• D. Kerosene
• Rationale: No. 6 oil is a heavy, residual oil that is thick at
room temperature and must be heated to lower its viscosity
for proper combustion in large industrial boilers.
9. A "Tri-Cock" or "Try-Cock" set on a large boiler is used for what
specific purpose?
• A. To blow down the water column to clear debris.
• B. To test the high-pressure alarm system.
• C. To manually verify the water level in the boiler if
the gauge glass is broken or unreliable.
• D. To inject chemicals directly into the steam drum.
• Rationale: Try-cocks are the secondary, manual method of
checking water level; steam from the top, water from the
bottom, and a mixture from the middle cock indicate a
proper level.
10. In a centralized HVAC system, what is the function of the
"Economizer" cycle?
• A. It reduces the speed of the fans to save electricity during
the night.
• B. It uses cool outdoor air to provide "free cooling"
for the building when the outdoor temperature is
lower than the indoor air temperature.
• C. It recycles used air to save on heating costs during the
winter.
• D. It shuts down the chiller when the building is unoccupied.
