Missouri (St. Louis County) Commercial
HVAC Servicer/Installer - 588-MO-SL
Contractor Exam
What is the minimum allowable clearance for a non-condensable storage tank in a
commercial HVAC system according to St. Louis County code?
The minimum allowable clearance is 24 inches for access and serviceability.
What refrigerant is commonly prohibited in new commercial HVAC installations in St.
Louis County due to environmental regulations?
R-22 is prohibited in new systems but may exist in older equipment.
How often must a registered HVAC contractor renew their license with St. Louis County?
Annually, by December 31st.
What is the maximum allowable length of a flexible duct connector in a commercial
HVAC system under Missouri mechanical code?
Fourteen inches unless otherwise specified for fire safety.
When must a pressure relief valve be installed on a commercial HVAC receiver?
When the receiver capacity exceeds the system’s minimum volume requirements as per
ASME code.
What is the required slope per foot for a horizontal drain line from an evaporator coil?
One-quarter inch per foot toward the drain.
Which test is required to verify a commercial HVAC system’s ductwork integrity in St.
Louis County?
A leakage test at 25% of design pressure, not to exceed 2% leakage.
,What is the minimum efficiency requirement for a commercial packaged rooftop unit
installed after 2020 in St. Louis County?
IEER of 15.0 or higher for units under 65,000 Btu/h.
Can an HVAC contractor install a used condensing unit in a new commercial build?
No, used equipment must be disclosed and may only be installed in existing systems
with county inspection approval.
What is the required fire damper rating for a duct penetration through a two-hour rated
wall?
One and one-half hours as per NFPA 90A.
How many pounds of refrigerant can a technician legally vent without recovery in
Missouri?
Zero; all refrigerants must be recovered per EPA Section 608.
What is the minimum pipe size for a natural gas line serving a 500,000 Btu/h rooftop
unit at 20 feet length with 0.5 in. w.c. drop?
One and one-quarter inch schedule 40 black iron.
Which agency enforces commercial HVAC mechanical code in St. Louis County?
The St. Louis County Department of Public Works, Division of Code Enforcement.
What type of brazing rod is required for joining copper refrigerant lines in a commercial
system?
15% silver-phosphorus alloy for copper-to-copper; 45% silver for copper-to-brass or
copper-to-steel.
What is the maximum allowable operating pressure for a low-pressure steam boiler in a
commercial building?
15 psig for steam, 160 psig for hot water per ASME Section IV.
, When is a permit not required for commercial HVAC repair in St. Louis County?
When replacing like-for-like components without altering circuitry, refrigerant charge, or
ductwork.
What is the minimum clearance from an air intake to a gas vent termination on a
commercial roof?
Ten feet horizontally, or three feet above the intake if closer.
What type of expansion tank is required for a closed-loop hydronic system exceeding 30
gallons of water volume?
A diaphragm-type or bladder-type expansion tank sized per system volume and
temperature rise.
What is the maximum refrigerant charge allowed in a commercial split system without a
low-ambient control?
No specific limit, but low-ambient controls are required if operation below 55°F ambient
is intended.
How must abandoned refrigerant piping be treated during a commercial renovation?
It must be removed or capped and labeled “ABANDONED REFRIGERANT LINE—DO NOT
USE.”
What is the minimum combustion air opening size for a 400,000 Btu/h gas furnace
located in a confined mechanical room?
One square inch per 1,000 Btu/h from outdoors, or 100 square inches from adjacent
indoor space with louvers.
What is the maximum allowable noise level for a commercial condensing unit adjacent
to a residential zone?
65 dBA at property line during daytime, 55 dBA nighttime.
HVAC Servicer/Installer - 588-MO-SL
Contractor Exam
What is the minimum allowable clearance for a non-condensable storage tank in a
commercial HVAC system according to St. Louis County code?
The minimum allowable clearance is 24 inches for access and serviceability.
What refrigerant is commonly prohibited in new commercial HVAC installations in St.
Louis County due to environmental regulations?
R-22 is prohibited in new systems but may exist in older equipment.
How often must a registered HVAC contractor renew their license with St. Louis County?
Annually, by December 31st.
What is the maximum allowable length of a flexible duct connector in a commercial
HVAC system under Missouri mechanical code?
Fourteen inches unless otherwise specified for fire safety.
When must a pressure relief valve be installed on a commercial HVAC receiver?
When the receiver capacity exceeds the system’s minimum volume requirements as per
ASME code.
What is the required slope per foot for a horizontal drain line from an evaporator coil?
One-quarter inch per foot toward the drain.
Which test is required to verify a commercial HVAC system’s ductwork integrity in St.
Louis County?
A leakage test at 25% of design pressure, not to exceed 2% leakage.
,What is the minimum efficiency requirement for a commercial packaged rooftop unit
installed after 2020 in St. Louis County?
IEER of 15.0 or higher for units under 65,000 Btu/h.
Can an HVAC contractor install a used condensing unit in a new commercial build?
No, used equipment must be disclosed and may only be installed in existing systems
with county inspection approval.
What is the required fire damper rating for a duct penetration through a two-hour rated
wall?
One and one-half hours as per NFPA 90A.
How many pounds of refrigerant can a technician legally vent without recovery in
Missouri?
Zero; all refrigerants must be recovered per EPA Section 608.
What is the minimum pipe size for a natural gas line serving a 500,000 Btu/h rooftop
unit at 20 feet length with 0.5 in. w.c. drop?
One and one-quarter inch schedule 40 black iron.
Which agency enforces commercial HVAC mechanical code in St. Louis County?
The St. Louis County Department of Public Works, Division of Code Enforcement.
What type of brazing rod is required for joining copper refrigerant lines in a commercial
system?
15% silver-phosphorus alloy for copper-to-copper; 45% silver for copper-to-brass or
copper-to-steel.
What is the maximum allowable operating pressure for a low-pressure steam boiler in a
commercial building?
15 psig for steam, 160 psig for hot water per ASME Section IV.
, When is a permit not required for commercial HVAC repair in St. Louis County?
When replacing like-for-like components without altering circuitry, refrigerant charge, or
ductwork.
What is the minimum clearance from an air intake to a gas vent termination on a
commercial roof?
Ten feet horizontally, or three feet above the intake if closer.
What type of expansion tank is required for a closed-loop hydronic system exceeding 30
gallons of water volume?
A diaphragm-type or bladder-type expansion tank sized per system volume and
temperature rise.
What is the maximum refrigerant charge allowed in a commercial split system without a
low-ambient control?
No specific limit, but low-ambient controls are required if operation below 55°F ambient
is intended.
How must abandoned refrigerant piping be treated during a commercial renovation?
It must be removed or capped and labeled “ABANDONED REFRIGERANT LINE—DO NOT
USE.”
What is the minimum combustion air opening size for a 400,000 Btu/h gas furnace
located in a confined mechanical room?
One square inch per 1,000 Btu/h from outdoors, or 100 square inches from adjacent
indoor space with louvers.
What is the maximum allowable noise level for a commercial condensing unit adjacent
to a residential zone?
65 dBA at property line during daytime, 55 dBA nighttime.
