CMC · California Mechanical Code
What are the construction, ventilation and makeup-air requirements for refrigeration machinery rooms?
Machinery rooms that house refrigerant equipment must be built tight and ventilated to the outdoors with dedicated makeup air located to avoid short‑circuiting; exhaust inlet heights, emergency airflow, detector activation, and whether ventilation runs continuously or is detector‑activated are all specified in the California Mechanical Code (see **§ 1106.0**, **§ 1106.4**, and **§ 1106.11.6.1**).
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Refrigeration machinery rooms must be constructed, ventilated, and supplied with makeup air so that refrigerant releases are detected and exhausted safely, temperatures remain within limits, and makeup air cannot short‑circuit to exhaust. Key controlling provisions are § 1106.0 (where machinery rooms are required and general requirements), § 1106.4 (natural ventilation sizing and openings), and § 1106.11.6.1 (mechanical ventilation operation requirements) of the California Mechanical Code.
The single most important requirement: machinery rooms must be ventilated to the outdoors (natural or mechanical) with makeup air provided directly from outside, with intakes and exhausts located to prevent short‑circuiting and to collect refrigerant where it will accumulate.
Requirements in detail
A. When a machinery room is required and construction basics
- A machinery room is required where specified in § 1106.0 (for example, certain refrigerant types, large systems, or other conditions listed in § 1106.1). Machinery rooms must provide access, headroom, restricted access signage, and be sized for maintenance access. § 1106.0 and § 1106.2 set the baseline construction and access rules.
- For rooms required by flammability or A2L/B2L rules, additional construction applies: tight noncombustible walls/floor/ceiling and 1‑hour fire resistive separations where required, and sealing of pipe penetrations. See § 1106.11.3 and related subsections.
B. Mechanical ventilation operation (continuous or detector‑activated)
- For machinery rooms covered by the A2L/B2L special rules, the mechanical ventilation system must either run continuously (and its failure must actuate an alarm) or be activated by refrigerant detector(s), per § 1106.11.6.1.
- Mechanical ventilation shall follow the more detailed mechanical ventilation requirements of § 1106.11.11 (fans, motor location, makeup‑air provisions, multispeed allowed, etc.).
C. Makeup‑air intakes and distribution
- Makeup air intakes must be provided directly from outside the building and fitted with backdraft dampers or approved flow‑control means to prevent reverse flow, per § 1106.6. Distribution must be arranged to provide thorough mixing and avoid short‑circuiting directly to the exhaust.
- Ducts for supply and exhaust to the machinery room shall serve no other area (separate dedicated ducts), per § 1106.2.8 / § 1106.11.11.1.
D. Natural ventilation sizing and location
- If natural (gravity) ventilation is used (allowed in certain outdoor penthouse/open‑structure conditions), the required free opening area is given by the equation F = √G where F = free opening area (ft²) and G = mass (lb) of refrigerant in the largest system (any part located in the machinery room), per § 1106.4. Locations of openings must be based on the refrigerant’s relative density to air.
E. Exhaust inlet location relative to refrigerant density
- Exhaust inlets must be placed near where refrigerant will concentrate:
- For refrigerants heavier than air, inlets within 1 foot (305 mm) of the lowest point of the room.
- For refrigerants lighter than air, inlets within 1 foot (305 mm) of the highest point of the room. These placement rules are in § 1106.2.8.
F. Emergency ventilation (Level 2) and normal ventilation (Level 1)
- An emergency ventilation system is required to remove accumulated refrigerant; the required emergency airflow for many refrigerant groups (A1, A2, A3, B1, B2, B3) is calculated as:
- Q = 100 × √G (Q in CFM; G = refrigerant mass in pounds) per § 1106.2.9.1.
- For Class 2L refrigerants (A2L/B2L machinery rooms), Level 1 ventilation (normal/trouble) rates are specified in Table 1106.11.11.2 as the greater of:
- 0.5 CFM/ft² of machinery room area, or
- 20 CFM per person — when operated while occupied; alternate temperature‑based rates apply when operable but not run full time. See § 1106.11.11.2 / Table 1106.11.11.2.
G. Temperature control
- Ventilation or mechanical cooling must maintain room temperature at not more than 104°F (40°C) under design loads and weather conditions (maximum temperature requirement in § 1106.7). For some Class 2L scenarios, ventilation must prevent a temperature rise greater than 18°F (10°C) above inlet air or a maximum of 122°F (50°C) when operable (see Table language in § 1106.11.11.2).
Decision‑relevant dimensions / values (quick reference table)
| Item / Value | Numeric value / rule | Code Reference |
|---|---|---|
| Natural ventilation free opening (F) | F = √G (ft²), G = refrigerant mass (lb) | § 1106.4 |
| Emergency ventilation (Q) | Q = 100 × √G (CFM) for A1/A2/A3/B1/B2/B3 refrigerants | § 1106.2.9.1 |
| Exhaust inlet placement | Within 1 foot (305 mm) of lowest point (heavier than air) or highest point (lighter than air) | § 1106.2.8 |
| Level 1 ventilation (Class 2L) | Greater of 0.5 CFM/ft² or 20 CFM/person (when occupied) | § 1106.11.11.2 / Table 1106.11.11.2 |
| Makeup air intake location | Directly from outdoors; fitted with backdraft damper; avoid short‑circuiting | § 1106.6 |
| Mechanical ventilation operation | Run continuously (failure alarms) or detector‑activated (per detectors) | § 1106.11.6.1 |
| Maximum machinery room temp | 104°F (40°C) (general); 122°F (50°C) in some Class 2L operable conditions | § 1106.7; § 1106.11.11.2 |
H. Equipment, detectors, controls, and safety
- Refrigerant detectors are required and must be located where refrigerant will concentrate; detectors trigger alarms and, at higher set points, must automatically shut down compressors, pumps, normally‑closed valves and other ignition sources per § 1106.11.6.2 / § 1106.11.8–1106.11.11. Multiport detectors are prohibited.
- Mechanical equipment controls, remote shutoff switches and ventilation fan controls must be located immediately outside the machinery room door and be on separate circuits as required in § 1106.11.7 and § 1107.1.10.
Exceptions & special cases
- Refrigerant detectors and some combustion‑air restrictions are not required in machinery rooms where carbon dioxide (R‑744) or water (R‑718) is the refrigerant (see exception in § 1106.5).
- Special additional rules apply for Group A2L and B2L refrigerants: a machinery room complying with § 1106.11 (and its detector/ventilation timing and setpoints) may be treated differently from standard flammable groups; see § 1106.11 and § 1107.1.7 for the conditional relaxations and added requirements.
- Where natural ventilation is allowed it applies to outdoor enclosures/penthouses located more than 20 feet (6096 mm) from building openings per § 1106.4.
Common mistakes
- Locating makeup‑air inlets so they short‑circuit directly to the exhaust (code requires mixing and positioning to avoid this). § 1106.6 and § 1106.2.8 prohibit short‑circuiting.
- Placing exhaust inlet heights contrary to refrigerant density guidance (violates § 1106.2.8; inhalation or accumulation points must be considered).
- Relying on building HVAC return air as makeup air or sharing ducts—makeup and exhaust ducts shall serve no other area, per § 1106.2.8 / § 1106.11.11.1.
- Using fan motors or non‑approved rotating elements inside exhaust ducts or using materials that can spark—mechanical ventilator construction rules are in § 1106.11.11.1.
- Not providing alarm on ventilation failure when continuous ventilation is required (see § 1106.11.6.1).
Worked example — concrete scenario
Scenario: Indoor machinery room contains the largest refrigerant charge of 200 lb of an A2/B2 refrigerant. The room is occupied during servicing and requires both Level 1 (normal) and emergency ventilation capability.
Emergency ventilation (Q) per § 1106.2.9.1:
- Q = 100 × √G = 100 × √200 = 100 × 14.142 = 1,414 CFM required for emergency exhaust.
Level 1 ventilation (Class 2L guidance if applicable) per Table 1106.11.11.2:
- If room area is 200 ft² and maximum expected occupants = 2:
- 0.5 CFM/ft² × 200 ft² = 100 CFM
- 20 CFM/person × 2 persons = 40 CFM
- Level 1 required = greater = 100 CFM (operated when occupied).
- If room area is 200 ft² and maximum expected occupants = 2:
Makeup air:
- Provide makeup air directly from outdoors sized at or above the exhausted CFM; install backdraft damper and position intake to promote mixing and avoid direct short‑circuiting per § 1106.6.
Detector and control:
- Install refrigerant detector(s) located where refrigerant would accumulate (low point if refrigerant heavier than air), with set points per Table 1106.11.10.2 to trigger Level 2 ventilation and alarms, and automatic shutdown of compressors per § 1106.11.6.2.
(If the exact refrigerant group or allowable OEL/RCL set points are needed, consult the refrigerant listing and Table 1102.3; those specific concentration values are outside the immediately quoted sections.)
Related provisions (quick list)
- § 1106.0 — Where machinery rooms are required and general scope.
- § 1106.2 — Refrigeration machinery room general requirements (access, openings, airflow, detectors).
- § 1106.4 — Natural ventilation sizing (F = √G) and location rules.
- § 1106.6 — Makeup‑air intakes; direct from outdoors; anti‑backflow.
- § 1106.7 — Maximum machinery room temperature limits.
- § 1106.11.6.1 — Mechanical ventilation operation (continuous or detector‑activated).
- § 1106.11.11 / Table 1106.11.11.2 — Mechanical ventilation design, Level 1 rates for Class 2L refrigerants.
- § 1107.1.7 — Special machinery room rules for Group A2L/B2L refrigerants (interaction with electrical code).
- § 1108.3 — Emergency shutoff location and requirements.
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1106.2.5 High relevance — show source text
(1) Combustion air shall be ducted from outside the machinery room and sealed in such a manner as to prevent refrigerant leakage from entering the combustion chamber.
(2) A refrigerant detector, that is in accordance with Section 1106.2.5, shall be installed to automatically shut down the combustion process in the event of refrigerant leak age.
Exception: Machinery rooms where carbon dioxide (R-744) or water (R-718) is the refrigerant.
1106.6 Ventilation Intake. Makeup air intakes to replace the exhaust air shall be provided to the refrigeration machinery room directly from outside the building. Intakes shall be located as required by other sections of the code and fitted with backdraft dampers or other approved flow-control means to prevent reverse flow. Distribution of makeup air shall be arranged to provide thorough mixing within the refrigeration machinery room to prevent short circuiting of the makeup air directly to the exhaust.
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REFRIGERATION
1106.11.6.1 Mechanical Ventilation. The machinery room shall have a mechanical ventilation system in accordance with Section 1106.11.11. The mechanical ventilation system shall:
(1) Run continuously, and failure of the mechanical ventilation system actuates an alarm, or
(2) Be activated by one or more refrigerant detectors, conforming to requirements of Section 1106.11.8. [ASHRAE 15:8.13.6.1] 1106.11.6.2 Detection System. Detection of refrigerant concentration that exceeds 25 percent of the LFL or the upper detection limit of the refrigerant detector, whichever is lower, shall automatically de-energize the following equipment in the machin ery room:
(1) Refrigerant compressors
(2) Refrigerant pumps
(3) Normally closed automatic refrigerant valves
(4) Other unclassified electrical sources of ignition with apparent power rating greater than 1 kVA, where the apparent power is the product of the circuit voltage and current rating. [ASHRAE 15:8.13.6.2] 1106.11.7 Mechanical Equipment Control. Remote control of the mechanical equipment in the refrigerating machinery room shall be provided immediately outside the machinery room door solely for the purpose of shutting down the equipment in an emergency. Ventilation fans shall be on a separate electrical circuit and have a control switch located immediately outside the machinery room door. [ASHRAE 15:8.13.7] 1106.11.8 Refrigerant Detectors. Each refrigerating machinery room in accordance with Section 1106.11 shall contain one or more refrigerant detectors in accordance with Section 1106.11.9. The detector(s) sensing element shall be located in areas where refrigerant from a leak will concentrate, with one or more set points that activate responses in accordance with Section 1106.11.10 for alarms and Section 1106.11.11 for mechanical ventilation. Multiport-type devices shall be prohibited. {ASHRAE 15:8.13.8} 1106.11.9 Refrigerant Detectors Requirements. Refrigerant detectors required by Section 1106.11 shall meet all of the following conditions:
CMC § 1106.2.9. High relevance — show source text
1106.2.9.
1106.2.8 Ventilation. Mechanical ventilation referred
to in Section 1106.2.7 shall be by one or more powerdriven fans capable of exhausting air from the machinery room at not less than the amount shown in accordance
with Section 1106.2.9.
To obtain a reduced airflow for normal ventilation, multiple fans or multispeed fans shall be used. Provision shall be made to supply makeup air to replace that being exhausted. Ducts for supply and exhaust to the machinery room shall serve no other area. The makeup air supply locations shall be positioned relative to the exhaust air locations to avoid short-circuiting. Inlets to the exhaust ducts shall be located in an area where refrigerant from a leak will concentrate, in consideration of the location of the replacement supply air paths, refrigerating machines, and the density of the refrigerant relative to air.
Inlets to exhaust ducts shall be within 1 foot (305 mm) of the lowest point of the machinery room for refrigerants that are heavier than air, and shall be within 1 foot (305 mm) of the highest point for refrigerants that are lighter than air. The discharge of the exhaust air shall be to the outdoors in such a manner as not to cause a nuisance or danger.
1106.2.9 Emergency Ventilation-Required Air- flow. An emergency ventilation system shall be required to exhaust an accumulation of refrigerant due to leaks or a rupture of the system. The emergency ventilation required shall be capable of removing air from the machinery room in not less than the airflow quantity in Section 1106.2.9.1. Where multiple refrigerants are present, then the highest airflow quantity shall apply.
1106.2.9.1 Ventilation - A1, A2, A3, B1, B2 and B3 Refrigerants. The emergency ventilation for A1, A2, A3, B1, B2 and B3 refrigerants shall have the capacity to provide mechanical exhaust at a rate as determined in accordance with Equation 1106.2.9.1.
Q = 100
√G (Equation 1106.2.9.1)Where:
Q = Air flow rate, CFM.
G = Refrigerant mass in largest system, pounds.
For SI units: 1 pound = 0.453 kg, 1 cubic foot per minute =
0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
1106.3 Normal Operation. A part of the refrigeration machinery room mechanical ventilation shall be in accordance with the following:
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REFRIGERATION
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CMC § 1106.11.10.1 High relevance — show source text
1106.11.10.1 Visual and Audio. The alarm shall
have visual and audible annunciation inside the refrigerating machinery room and outside each entrance to the refrigerating machinery room.
[ASHRAE 15:8.13.10.1] 1106.11.10.2 Detector Activation. The refrigerant detector set points shall activate an alarm in accordance with the type of reset in Table 1106.11.10.2. Manual reset type alarms shall have the reset located inside the refrigerating machinery room. [ASHRAE 15:8.13.10.2]
TABLE 1106.11.10.2 REFRIGERANT DETECTOR SET POINTS, RESPONSE TIMES, ALARMS, AND VENTILATION LEVELS
[ASHRAE 15: TABLE 8-1]
LIMIT VALUE RESPONSE TIME
(seconds)ALARM TYPE ALARM RESET TYPE VENTILATION RATE VENTILATION
RESET TYPESet point≤ OEL ≤300 Trouble Alarm Automatic Level 1 Automatic Set point≤ RCL ≤15 Emergency Alarm Manual Level 2 Manual 2025 CALIFORNIA MECHANICAL CODE 235
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REFRIGERATION
1106.11.10.3 Alarm Levels. Alarms set at levels
other than Table 1106.11.10.2 (such as IDLH) and automatic reset alarms are permitted in addition to those required by Section 1106.11.10. The meaning of each alarm shall be clearly marked by signage near the annunciators. [ASHRAE 15:8.13.10.3]
1106.11.10.4 Emergency. In the event of a failure during a refrigerant detector self-test in accordance with Section 1106.11.9(5), a trouble alarm signal shall be transmitted to an approved monitored location. [ASHRAE 15:8.13.10.4]
1106.11.11 Mechanical Ventilation. Machinery rooms, in accordance with Section 1106.11, shall be vented to the outdoors, using mechanical ventilation in accordance with Section 1106.11.11.1, Section 1106.11.11.2, and Section 1106.11.11.3. [ASHRAE 15:8.13.11]
1106.11.11.1 Mechanical Ventilation Require- ments. Mechanical ventilation referred to in Sec tion 1106.11.11 shall be in accordance with all of
the following:
(1) Include one or more power-driven fans capable of exhausting air from the machinery room; multispeed fans shall be permitted.
(2) Electric motors driving fans shall not be placed inside ducts; fan rotating elements shall be nonferrous or non-sparking, or the casing shall consist of or be lined with such material.
(3) Include provision to supply make-up air to replace that being exhausted; ducts for supply to and exhaust from the machinery room shall serve no other area; the makeup air supply locations shall be positioned relative to the exhaust air locations to avoid short circuiting.
CMC § 1106.11. High relevance — show source text
The alarm shall annunciate visual and audible alarms inside the refrigeration machinery room and outside each entrance to the refrigeration machinery room. The alarms required in this section shall be of the manual reset type with the reset located inside the refrigeration machinery room. Alarms set at other levels, such as IDLH, and automatic reset alarms shall be permitted in addition to those required in accordance with this section. The meaning of each alarm shall be clearly marked by signage near the annunciator.
Exception: Refrigerant detectors are not required where only systems using R-718 (water) are located in the refrigeration machinery room. For Group A2L and B2L, refrigerant detectors shall comply with Section 1106.11.
1106.2.6 Refrigerant Detectors. Refrigerant detectors required in accordance with Section 1106.2.5 or Section 1107.1.7 shall meet all of the following conditions:
(1) The refrigerant detector shall perform automatic self-testing of sensors. Where a failure is detected, a trouble signal shall be activated.
(2) The refrigerant detector shall have one or more set points to activate responses in accordance with Section 1106.2.5 or Section 1107.1.7.
(3) The refrigerant detector as installed, including any sampling tubes, shall activate responses within a time not to exceed 30 seconds after exposure to refriger
ant concentration exceeding the set point value specified in Section 1106.2.5 or Section 1107.1.7.
1106.2.7 Mechanical Ventilation. Machinery rooms shall be vented to the outdoors, utilizing mechanical ventilation in accordance with Section 1106.2.8 and Section
1106.2.9.
1106.2.8 Ventilation. Mechanical ventilation referred
to in Section 1106.2.7 shall be by one or more powerdriven fans capable of exhausting air from the machinery room at not less than the amount shown in accordance
with Section 1106.2.9.
To obtain a reduced airflow for normal ventilation, multiple fans or multispeed fans shall be used. Provision shall be made to supply makeup air to replace that being exhausted. Ducts for supply and exhaust to the machinery room shall serve no other area. The makeup air supply locations shall be positioned relative to the exhaust air locations to avoid short-circuiting. Inlets to the exhaust ducts shall be located in an area where refrigerant from a leak will concentrate, in consideration of the location of the replacement supply air paths, refrigerating machines, and the density of the refrigerant relative to air.
Inlets to exhaust ducts shall be within 1 foot (305 mm) of the lowest point of the machinery room for refrigerants that are heavier than air, and shall be within 1 foot (305 mm) of the highest point for refrigerants that are lighter than air. The discharge of the exhaust air shall be to the outdoors in such a manner as not to cause a nuisance or danger.
1106.2.9 Emergency Ventilation-Required Air- flow. An emergency ventilation system shall be required to exhaust an accumulation of refrigerant due to leaks or a rupture of the system. The emergency ventilation required shall be capable of removing air from the machinery room in not less than the airflow quantity in Section 1106.2.9.1. Where multiple refrigerants are present, then the highest airflow quantity shall apply.
CMC § 1106.7 High relevance — show source text
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1106.7 Maximum Temperature. Ventilation or mechanical cooling systems shall be provided to maintain a temperature of not more than 104°F (40°C) in the refrigerant machinery room under design load and weather conditions. 1106.8 Refrigerant Parts in Air Duct. Joints and refrigerant-containing parts of a refrigerating system located in an air duct carrying conditioned air to and from an occupied space shall be constructed to withstand a temperature of 700°F (371°C) without leakage into the airstream. [ASHRAE 15:8.8]
1106.9 Dimensions. Refrigeration machinery rooms shall be of such dimensions that system parts are readily accessible with approved space for maintenance and operations. An unobstructed walking space not less than 36 inches (914 mm) in width and 80 inches (2032 mm) in height shall be maintained throughout, allowing free access to not less than two sides of moving machinery and approaching each stop valve. Access to refrigeration machinery rooms shall be restricted to authorized personnel and posted with a permanent sign. 1106.10 Exits. Exits shall comply with the building code for special hazards. 1106.11 Machinery Room, A2L and B2L. When required by Section 1106.1, machinery rooms shall comply with Section 1106.11.1 through Section 1106.11.6. [ASHRAE 15:8.13]
1106.11.1 Flame-Producing Device. There shall be no flame-producing device or hot surface over 1290°F (700°C) in the room, other than that used for maintenance or repair, unless installed in accordance with Section 1106.5. [ASHRAE 15:8.13.1] 1106.11.2 Communicating Spaces. Doors communicating with the building shall be approved, self-closing, tight-fitting fire doors. [ASHRAE 15:8.13.2]
1106.11.3 Noncombustible Construction. Walls, floor, and ceiling shall be tight and of noncombustible construction. Walls, floor, and ceiling separating the refrigerating machinery room from other occupied spaces shall be of at least one-hour fire-resistive construction. [ASHRAE 15:8.13.3] 1106.11.4 Exterior Openings. Exterior openings, if present, shall not be under any fire escape or any open stairway. [ASHRAE 15:8.13.4] 1106.11.5 Pipe Penetrations. All pipes piercing the interior walls, ceiling, or floor of such rooms shall be tightly sealed to the walls, ceiling, or floor through which they pass. [ASHRAE 15:8.13.5] 1106.11.6 Machinery Room Designation. When any refrigerant of Groups A2, A3, B2, or B3 are used, the machinery room shall be designated as Class I, Division 2 hazardous (classified) electrical location in accordance with NFPA 70.
CMC § 8.13.6 High relevance — show source text
[ASHRAE 15:8.13.6]
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(1) Operated, where occupied, to supply not less than 0.5 CFM/ft [2] [2.54 L/(s•m [2] )] of machinery room area or 20 cubic feet per minute (9.44 L/s) per person.
(2) Operable, where occupied at a volume required to not exceed the higher of a temperature rise of 18°F (10°C) above inlet air temperature or a maximum temperature of 122°F (50°C).
1106.4 Natural Ventilation. When a refrigerating system is located outdoors more than 20 feet (6096 mm) from building openings and is enclosed by a penthouse, lean-to, or other open structure, natural or mechanical ventilation shall be provided. The requirements for such natural ventilation shall be in accordance with the following:
(1) The free-aperture cross section for the ventilation of a machinery room shall be not less than as determined in accordance with Equation 1106.4.
F = √ G (Equation 1106.4)
Where:
F = The free opening area, ft [2] (m [2] ).
G = The mass of refrigerant in the largest system, any part of which is located in the machinery room, pounds.
For SI units: 1 square foot = 0.0929 m [2], 1 pound = 0.453 kg
(2) Locations of the gravity ventilation openings shall be based on the relative density of the refrigerant to air.
[ASHRAE 15:8.14]
1106.5 Combustion Air. No open flames that use combustion air from the machinery room shall be installed where refrigerant is used. Combustion equipment shall not be installed in the same machinery room with refrigerant-containing equipment except under one of the following conditions:
(1) Combustion air shall be ducted from outside the machinery room and sealed in such a manner as to prevent refrigerant leakage from entering the combustion chamber.
(2) A refrigerant detector, that is in accordance with Section 1106.2.5, shall be installed to automatically shut down the combustion process in the event of refrigerant leak age.
Exception: Machinery rooms where carbon dioxide (R-744) or water (R-718) is the refrigerant.
1106.6 Ventilation Intake. Makeup air intakes to replace the exhaust air shall be provided to the refrigeration machinery room directly from outside the building. Intakes shall be located as required by other sections of the code and fitted with backdraft dampers or other approved flow-control means to prevent reverse flow. Distribution of makeup air shall be arranged to provide thorough mixing within the refrigeration machinery room to prevent short circuiting of the makeup air directly to the exhaust.
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REFRIGERATION
1106.11.6.1 Mechanical Ventilation. The machinery room shall have a mechanical ventilation system in accordance with Section 1106.11.11. The mechanical ventilation system shall:
(1) Run continuously, and failure of the mechanical ventilation system actuates an alarm, or
CMC § 1106.2.9 High relevance — show source text
1106.2.9 Emergency Ventilation-Required Air- flow. An emergency ventilation system shall be required to exhaust an accumulation of refrigerant due to leaks or a rupture of the system. The emergency ventilation required shall be capable of removing air from the machinery room in not less than the airflow quantity in Section 1106.2.9.1. Where multiple refrigerants are present, then the highest airflow quantity shall apply.
1106.2.9.1 Ventilation - A1, A2, A3, B1, B2 and B3 Refrigerants. The emergency ventilation for A1, A2, A3, B1, B2 and B3 refrigerants shall have the capacity to provide mechanical exhaust at a rate as determined in accordance with Equation 1106.2.9.1.
Q = 100
√G (Equation 1106.2.9.1)Where:
Q = Air flow rate, CFM.
G = Refrigerant mass in largest system, pounds.
For SI units: 1 pound = 0.453 kg, 1 cubic foot per minute =
0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
1106.3 Normal Operation. A part of the refrigeration machinery room mechanical ventilation shall be in accordance with the following:
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REFRIGERATION
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1106.7 Maximum Temperature. Ventilation or mechanical cooling systems shall be provided to maintain a temperature of not more than 104°F (40°C) in the refrigerant machinery room under design load and weather conditions. 1106.8 Refrigerant Parts in Air Duct. Joints and refrigerant-containing parts of a refrigerating system located in an air duct carrying conditioned air to and from an occupied space shall be constructed to withstand a temperature of 700°F (371°C) without leakage into the airstream. [ASHRAE 15:8.8]
1106.9 Dimensions. Refrigeration machinery rooms shall be of such dimensions that system parts are readily accessible with approved space for maintenance and operations. An unobstructed walking space not less than 36 inches (914 mm) in width and 80 inches (2032 mm) in height shall be maintained throughout, allowing free access to not less than two sides of moving machinery and approaching each stop valve. Access to refrigeration machinery rooms shall be restricted to authorized personnel and posted with a permanent sign. 1106.10 Exits. Exits shall comply with the building code for special hazards. 1106.11 Machinery Room, A2L and B2L. When required by Section 1106.1, machinery rooms shall comply with Section 1106.11.1 through Section 1106.11.6. [ASHRAE 15:8.13]
CMC § 1106.11.11.4 High relevance — show source text
1106.11.11.4 Level 2 Ventilation Rate. When required by Section 1106.11.11.3, the total airflow for Level 2 ventilation shall be not less than the airflow rate determined by Figure 1106.11.11.4.
[ASHRAE 15:8.13.11.4]
1107.0 Machinery Room, Special Requirements.
1107.1 General. In cases specified in the rules of Section 1106.1, a refrigeration machinery room shall comply with the special requirements in accordance with Section 1107.1.1 through Section 1107.1.10, in addition to Section 1106.2.
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1107.1.1 Flame-Producing Devices. There shall be no flame-producing device or continuously operating hot surface over 800°F (427°C) permanently installed in the room.
1107.1.2 Doors. Doors communicating with the building shall be approved, self-closing, tight-fitting fire doors.
1107.1.3 Walls, Floors, and Ceilings. Walls, floor, and ceiling shall be tight and of noncombustible construction. Walls, floor, and ceiling separating the refrigeration machinery room from other occupied spaces shall be not less than one-hour fire-resistive construction.
1107.1.4 Machinery Rooms. The refrigeration machinery room shall have a door that opens directly to the outdoors or through a vestibule equipped with selfclosing, tight-fitting doors. 1107.1.5 Exterior Openings. Exterior openings, where present, shall not be under a fire escape or an open stair way. 1107.1.6 Sealing. All pipes piercing the interior walls, ceiling, or floor of such rooms shall be tightly sealed to the walls, ceiling, or floor through which they pass. 1107.1.7 Group A2L and B2L Refrigerants. Where refrigerant of Groups A2L or B2L are used, the requirements of Class 1, Division 2, of the California Electrical Code, shall not apply to the machinery room provided that the conditions in Section 1107.1.7.1 through Section 1107.1.7.3 are met.
1107.1.7.1 Mechanical Ventilation. The mechanical ventilation system in the machinery room is run continuously in accordance with Section 1106.11.6.1 and failure of the mechanical ventilation system actuates an alarm, or the mechanical ventilation system in the machinery room is activated by one or more refrigerant detectors, in accordance with the requirements of Section 1106.11.11.
1107.1.7.2 Refrigeration Detectors. For the refrigerant detection required in Section 1106.2.5, detection of refrigerant concentration that exceeds 25 percent of the LFL or the upper detection limit of the refrigerant detector, whichever is lower, shall automatically de-energize the following equipment in the machinery room:
(1) refrigerant compressors
(2) refrigerant pumps
(3) normally-closed automatic refrigerant valves
CMC § 1106.11.11.1 High relevance — show source text
refrigerating machinery room mechanical ventilation in Section 1106.11.11.1 shall exhaust at an air flow rate not less than shown in Table 1106.11.11.2.
[ASHRAE 15:8.13.11.2]
TABLE 1106.11.11.2
LEVEL 1 VENTILATION RATE FOR CLASS 2L REFRIGERANTS
[ASHRAE 15: TABLE 8-2]
STATUS AIRFLOW
Operated when occupied and
operated when activated in
accordance with Section
1106.11.9(3) and Table
1106.11.10.2The greater of the following:
(1) 0.5 ft3/min per ft3 of
machinery room area, or
(2) 20 ft3/min per person
Operable when occupiedWith or without mechanical
cooling of the machinery room,
the greater of:
(1) The airflow rate required to
not exceed a temperature
rise of 18°F above inlet air
temperature or
(2) The airflow rate required to
not exceed a maximum air
temperature of 122°F in the
machinery room.For SI units: °C = °F (5/9), 1 cubic foot = 0.0283 m [3], 1 cubic foot per minute = 0.0283 m [3] /min, 1 cubic foot per minute = 0.4719 L/s
1106.11.11.3 Level 2 Ventilation. A part of the refrigerating machinery room mechanical ventilation referred to in Section 1106.11.11.1 shall exhaust an accumulation of refrigerant due to leaks or a rupture of a refrigerating system, or portion thereof, in the machinery room. The refrigerant detectors required in accordance with Section 1106.11.8 shall activate ventilation at a set point and response time in accordance with Table 1106.11.10.2, at an airflow rate not less than the value determined in accordance
with Section 1106.11.11.4.
When multiple refrigerant designations are in the machinery room, evaluate the required airflow according to each refrigerating system, and the highest airflow quantity shall apply.
Ventilation reset shall be in accordance with the type of reset in Table 1106.11.10.2. Manual-type ventilation reset shall have the reset located inside the refrigerating machinery room. [ASHRAE 15:8.13.11.3]
1106.11.11.4 Level 2 Ventilation Rate. When required by Section 1106.11.11.3, the total airflow for Level 2 ventilation shall be not less than the airflow rate determined by Figure 1106.11.11.4.
[ASHRAE 15:8.13.11.4]
1107.0 Machinery Room, Special Requirements.
1107.1 General. In cases specified in the rules of Section 1106.1, a refrigeration machinery room shall comply with the special requirements in accordance with Section 1107.1.1 through Section 1107.1.10, in addition to Section 1106.2.
CMC § 1105.0 High relevance — show source text
1105.0 General Requirements . . . . . . . . . 231
1105.1 Human Comfort . . . . . . . . . . . . . . 231
1105.2 Supports and Anchorage . . . . . . . 231
1105.3 Access . . . . . . . . . . . . . . . . . . . . . 231
1105.4 Illumination and Service
Receptacles . . . . . . . . . . . . . . . . . 231
1105.5 Ventilation of Rooms
Containing Condensing Units . . . . 231
1105.6 Prohibited Locations . . . . . . . . . . . 232
1105.7 Condensate . . . . . . . . . . . . . . . . . 232
1105.8 Defrost . . . . . . . . . . . . . . . . . . . . . 232
1105.9 Overflows . . . . . . . . . . . . . . . . . . . 232
1105.10 Condensate, Defrost, and Overflow Disposal. . . . . . . . . . . . . 232
1105.11 Refrigerant Port Protection . . . . . . 232
1105.12 Storage . . . . . . . . . . . . . . . . . . . . . 232
1106.0 Refrigeration Machinery Rooms . . 232
1106.1 Where Required . . . . . . . . . . . . . . 232
1106.2 Refrigeration Machinery Room, General Requirements . . . . . . . . . 232
1106.3 Normal Operation . . . . . . . . . . . . . 233
1106.4 Natural Ventilation . . . . . . . . . . . . 234
1106.5 Combustion Air . . . . . . . . . . . . . . . 234
1106.6 Ventilation Intake . . . . . . . . . . . . . 234
1106.7 Maximum Temperature . . . . . . . . 234
1106.8 Refrigerant Parts in Air Duct. . . . . 234
1106.9 Dimensions. . . . . . . . . . . . . . . . . . 234
1106.10 Exits . . . . . . . . . . . . . . . . . . . . . . . 234
1106.11 Machinery Room, A2L and B2L . . 234
Table 1106.11.10.2 Refrigerant Detector Set Points, Response Times, Alarms, and Ventilation Levels . . . . . . . . . . . . . 235
Table 1106.11.11.2 Level 1 Ventilation Rate for
Class 2L Refrigerants . . . . . . . . . . . 236
1107.0 Machinery Room, Special Requirements . . . . . . . . . . . . . . . . 236
1107.1 General. . . . . . . . . . . . . . . . . . . . . 236
1108.0 Refrigeration Machinery Room Equipment and Controls . . . . . . . . 237
1108.1 General. . . . . . . . . . . . . . . . . . . . . 237
CMC § 204.0 High relevance — show source text
LOW-PRESSURE
HOT-WATER-HEATING BOILER
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
LOW-PRESSURE STEAM-HEATING BOILER
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204.0
LOW-WATER CUTOFF . . . . . . . . . . . . . . . . . . . . . . . 1008.0
LOWER FLAMMABILITY LIMIT (LFL)
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.0
Product conveying ducts . . . . . . . . . . . . . . 505.1, 505.3
Refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1104.4
– M –
MACHINERY
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215.0
MACHINERY ROOM, REFRIGERATION
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215.0
Detectors and alarms . . . . . . . . . . . . . . . . . . . . 1106.2.9
Equipment and controls in. . . . . . . . . . . . . . . . . . 1108.0
Ventilation of . . . . . . . . . . . . . . . . . . . 1106.2.7, 1106.2.8
Where required . . . . . . . . . . . . . . . . . . . . . . . . . . 1106.0
MAKEUP AIR . . . . . . . . . . . . . . . . . . . . . . (see Air, Makeup)
MARKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302.1.1
MASONRY, CHIMNEYS . . . . . . . . . (see Chimney, masonry)
MATERIALS
Alternate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302.2
For construction of
hoods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508.3
For piping, containers, and valves of
refrigeration systems . . . . . . . . . . . . . . . . . . . . 1109.1
For ducts . . . . . . . . . . . . . . . . . . . 506.1, 510.5.1, 602.0
CMC § 1107.1.7.1 High relevance — show source text
1107.1.7.1 Mechanical Ventilation. The mechanical ventilation system in the machinery room is run continuously in accordance with Section 1106.11.6.1 and failure of the mechanical ventilation system actuates an alarm, or the mechanical ventilation system in the machinery room is activated by one or more refrigerant detectors, in accordance with the requirements of Section 1106.11.11.
1107.1.7.2 Refrigeration Detectors. For the refrigerant detection required in Section 1106.2.5, detection of refrigerant concentration that exceeds 25 percent of the LFL or the upper detection limit of the refrigerant detector, whichever is lower, shall automatically de-energize the following equipment in the machinery room:
(1) refrigerant compressors
(2) refrigerant pumps
(3) normally-closed automatic refrigerant valves
1107.1.7.3 Machinery Rooms. The machinery room shall comply with Section 1106.11. 1107.1.8 Group A2, A3, B2, or B3 Refrigerants. Where any refrigerant of Groups A2, A3, B2, or B3 are used, the machinery room shall comply with Class 1, Division 2, of of the California Electrical Code .
1107.1.9 Refrigeration Systems. As part of the mechanical ventilation system in accordance with Section 1106.2.8, refrigeration systems that contain more
than 110 pounds (50 kg) of any Group A2L, A2, A3, B2L, B2, or B3, refrigerant shall have not less than one exhaust air inlet located adjacent to each system not more than 9 feet (3 m) away.
1107.1.10 Remote Control. Remote control of the
mechanical equipment in the refrigeration machinery room shall be provided immediately outside the machinery room door solely for the purpose of shutting down the equipment in an emergency. Ventilation fans shall be on a separate electrical circuit and have a control switch located immediately outside the machinery room door.
1108.0 Refrigeration Machinery Room Equipment and Controls.
1108.1 General. Equipment, piping, ducts, vents, or similar devices that are not essential for the refrigeration process, maintenance of the equipment, or for the illumination, ventilation, or fire protection of the room shall not be placed in or pass through a refrigeration machinery room.
1108.2 Electrical. Electrical equipment and installations shall comply with California Electrical Code . The refrigeration machinery room shall not be classified as a hazardous location except as provided in Section 1107.1.7 or Section 1107.1.8.
1108.3 Emergency Shutoff. A clearly identified emergency shutoff switch of the break-glass type or with an approved tamper-resistant cover shall be provided immediately adjacent to and outside of the principal refrigeration machinery room entrance. The switch shall provide off-only control of refrigerant compressors, refrigerant pumps, and normally-closed automatic refrigerant valves located in the machinery room. For other than A1 and B1 refrigerants, emergency shutoff shall be automatically activated by refrigerant Alarm 2 in accordance with Section 1106.2.5.
Frequently asked questions
Can makeup air be taken from the building HVAC return?
No. Makeup air for a refrigeration machinery room must be provided directly from outside and the supply/exhaust ducts must serve no other area, per § 1106.6 and § 1106.2.8.
Where should exhaust inlets be located for heavy refrigerants?
Exhaust inlets must be within 1 foot (305 mm) of the lowest point of the machinery room for refrigerants heavier than air, as required by § 1106.2.8.
Is continuous ventilation always required?
No. For some machinery rooms the mechanical ventilation must either run continuously (with failure alarm) or be activated by refrigerant detectors per § 1106.11.6.1.
How do I size emergency ventilation?
For A1/A2/A3/B1/B2/B3 refrigerants use Q = 100 × √G (CFM), where G is the refrigerant mass in the largest system, per § 1106.2.9.1.
Are refrigerant detectors required for CO2 (R‑744)?
No — the Code’s exception in § 1106.5 exempts machinery rooms using carbon dioxide (R‑744) or water (R‑718) from some combustion‑air detector requirements. Confirm other detector obligations in related sections.
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