Mechanical Ventilation
NYC Mechanical Code § MC 403
in effectSection MC 403: Mechanical Ventilation
403.1 Ventilation system.
Mechanical ventilation shall be provided by a method of supply air and return or exhaust air. The amount of supply air shall be approximately equal to the amount of return and exhaust air. The system shall not be prohibited from producing negative or positive pressure; such pressures shall not result in door opening forces in excess of those indicated in the New York City Building Code and shall not prevent doors from closing as required by the New York City Building Code. The method to convey ventilation air shall be designed and installed in accordance with Chapter 6.
403.2 Outdoor air required.
The minimum outdoor airflow rate shall be determined in accordance with Section 403.3.1.1.
Exception: The minimum required rate of outdoor air may be reduced where the registered design professional demonstrates that an engineered ventilation system is designed in accordance with ASHRAE 62.1 Indoor Air Quality Procedure.
403.2.1 Recirculation of air.
The outdoor air required by Section 403.3.1.1 shall not be recirculated. Air in excess of that required by Section 403.3.1.1 shall not be prohibited from being recirculated as a component of supply air to building spaces, except that:
1. Ventilation air shall not be recirculated from one dwelling unit to another or to dissimilar occupancies.
2. Supply air to a swimming pool and associated deck areas shall not be recirculated unless such air is dehumidified to maintain the relative humidity of the area at 60 percent or less. Air from this area shall not be recirculated to other uses or occupancies.
3. Where mechanical exhaust is required by Note b in Table 403.3.1.1, recirculation of air from such spaces shall be prohibited. Recirculation of air that is contained completely within such spaces shall not be prohibited. Where recirculation of air is prohibited, all air supplied to such spaces shall be exhausted, including any air in excess of that required by Table 403.3.1.1.
4. Where mechanical exhaust is required by Note g in Table 403.3.1.1, mechanical exhaust is required and recirculation is prohibited. Recirculation of air that is contained completely within such spaces shall not be prohibited.
403.2.2 Transfer air.
Except where recirculation from such spaces is prohibited by Table 403.3.1.1, air transferred from occupiable spaces is not prohibited from serving as makeup air for required exhaust systems in such spaces as kitchens, baths, toilet rooms, elevators and smoking lounges. The amount of transfer air and exhaust air shall be sufficient to provide the flow rates as specified in Section 403.3.1.1. The required outdoor airflow rates specified in Table 403.3.1.1 shall be introduced directly into such spaces or into the occupied spaces from which air is transferred or a combination of both.
403.3 Outdoor air and local exhaust airflow rates.
Buildings that are not more than three stories in height above grade plane, and that (i) are within Occupancy Group R-2 or Occupancy Group R-3, (ii) are adult homes or enriched living housing as described in Section 308.3.1 of the New York City Building Code, within Occupancy Group I-1 and have 16 occupants or fewer, or (iii) are community residences or intermediate-care facilities as described in Section 308.3.2 of the New York City Building Code, shall be provided with outdoor air and local exhaust in accordance with Section 403.3.1.1.2. All other buildings intended to be occupied shall be provided with outdoor air and local exhaust in accordance with Sections 403.3.1.1 through 403.3.1.6.
403.3.1 Reserved.
403.3.1.1 Outdoor airflow rate.
Ventilation systems shall be designed to have the capacity to supply the minimum outdoor airflow rate determined in accordance with this section. In each occupiable space and, where required, each habitable space, the ventilation system shall be designed to deliver the required rate of outdoor airflow to the breathing zone. The occupant load utilized for design of the ventilation system shall be not less than the number determined from the estimated maximum occupant load rate indicated in Table 403.3.1.1. Ventilation rates for occupancies not represented in Table 403.3.1.1 shall be those for a listed occupancy classification that is most similar in terms of occupant density, activities and building construction; or shall be determined by an approved engineering analysis. The ventilation system shall be designed to supply the required rate of ventilation air continuously during the period the building is occupied, except as otherwise stated in other provisions of the code.
With the exception of non-tobacco hookah establishments, the ventilation rates in Table 403.3.1.1 are based on the absence of smoking in occupiable spaces. Where smoking is anticipated in a space other than a non-tobacco hookah establishment, the ventilation system serving the space shall be designed to provide ventilation over and above that required by Table 403.3.1.1 in accordance with accepted engineering practice.
Exceptions:
1. The occupant load is not required to be determined based on the estimated maximum occupant load rate indicated in Table 403.3.1.1 where approved statistical data documents the accuracy of an alternate anticipated occupant load.
2. The occupant load used in computing the required ventilation shall be the maximum number who will occupy the room or space simultaneously during any 2-hour period.
3. Dynamic reset (Demand Controlled Ventilation). The system may be designed to reset the design outdoor air intake airflow and/or space or zone airflow as operating conditions change. Dynamic reset shall be designed in accordance with ASHRAE 62.1 and comply with footnote k of Table 403.3.1.1. These conditions include, but are not limited to:
3.1. Variations in occupancy or ventilation airflow in one or more individual zones for which ventilation airflow requirements will be reset. Note: Examples of measures for estimating such variations include: occupancy scheduled by time of day, a direct count of occupants, or an estimate of occupancy or ventilation rate per person using occupancy sensors such as those based on indoor CO2 concentrations.
3.2. Variations in the efficiency with which outdoor air is distributed to the occupants under different ventilation system airflows and temperatures.
3.3. A higher fraction of outdoor air in the air supply due to intake of additional outdoor air for free cooling or exhaust air makeup.
Table 403.3.1.1
Minimum Ventilation Rates
Occupancy Classification Occupant Density #/1,000 ft2 a People Outdoor Airflow Rate in Breathing Zone, Rp cfm/person Area Outdoor Airflow Rate in Breathing Zone, Ra cfm/ft2 a Exhaust Airflow Rate cfm/ft2 a
Correctional facilities
Booking/waiting 50 7.5 0.06 —
Cells
without plumbing fixtures 25 5 0.12 —
with plumbing fixtures g 25 5 0.12 1.0
Day room 30 5 0.06 —
Dining halls (see food and beverage service) — — — —
Guard stations 15 5 0.06 —
Dry cleaners, laundries
Coin-operated dry cleaner 20 15 — —
Coin-operated laundries 20 7.5 0.06 —
Commercial dry cleaner l 30 30 — —
Commercial laundry 10 25 — —
Storage, pick up 30 7.5 0.12 —
Education
Art classroom g 20 10 0.18 0.7
Auditoriums 150 5 0.06 —
Classrooms (ages 5-8) 25 10 0.12 —
Classrooms (age 9 plus) 35 10 0.12 —
Computer lab 25 10 0.12 —
Corridors (see public spaces) — — — —
Day care (through age 4) 25 10 0.18 —
Lecture classroom 65 7.5 0.06 —
Lecture hall (fixed seats) 150 7.5 0.06 —
Locker/dressing rooms g — — — 0.25
Media center 25 10 0.12 —
Multiuse assembly 100 7.5 0.06 —
Music/theater/dance 35 10 0.06 —
Science laboratories g, k 25 10 0.18 1.0
Sports locker rooms g — — — 0.5
Wood/metal shops g 20 10 0.18 0.5
Food and beverage service
Bars, cocktail lounges 100 7.5 0.18 —
Cafeteria, fast food 100 7.5 0.18 —
Dining rooms 70 7.5 0.18 —
Kitchens (cooking) b — — — 0.7
Non-tobacco smoking establishments b 70 60 — —
Hotels, motels, resorts and dormitories
Bathrooms/toilet – private g — — — 25/50 f
Bedroom/living room 10 5 0.06 —
Conference/meeting 50 5 0.06 —
Dormitory sleeping areas 20 5 0.06 —
Gambling casinos 120 7.5 0.18 —
Lobbies / prefunction 30 7.5 0.06 —
Multipurpose assembly 120 5 0.06 —
Laboratories j
Biological — — 1.0 1.0
Chemical — — 1.0 1.0
Industrial and nonteaching — — 1.0 1.0
Nonproduction chemical labs — — 1.0 1.0
Offices
Conference rooms 50 5 0.06 —
Main entry lobbies 10 5 0.06 —
Office spaces 5 5 0.06 —
Reception areas 30 5 0.06 —
Telephone/data entry 60 5 0.06 —
Private dwellings, single and multiple
Garages, common for multiple units b — — — 0.75
Kitchens and Kitchenettes b, m — — — 25/100 f
Living areas c, i Based upon number of bedrooms. First bedroom, 2; each additional 0.35 ACH but not less than 15 cfm/person — —
Toilet rooms and bathrooms g — — — 20/50 f
Public spaces
Corridors — — 0.06 —
Courtrooms 70 5 0.06 —
Elevator car — — — 1.0
Legislative chambers 50 5 0.06 —
Libraries 10 5 0.12 —
Museums (children's) 40 7.5 0.12 —
Museums/galleries 40 7.5 0.06 —
Places of religious worship 120 5 0.06 —
Shower room (per shower head) g — — — 50/20 f
Toilet rooms – public g — — — 50/70 e
Retail stores, sales floors and showroom floors
Dressing rooms — — — 0.25
Mall common areas 40 7.5 0.06 —
Sales 15 7.5 0.12 —
Shipping and receiving — — 0.12 —
Smoking lounges and non-tobacco smoking establishments b 70 60 — —
Storage rooms — — 0.12 —
Warehouses (see storage) — — — —
Specialty shops
Automotive motor-fuel dispensing stations b — — — 1.5
Barber 25 7.5 0.06 0.5
Beauty salons (without nail salon services) b 25 20 0.12 0.6
Embalming room b — — — 2.0
Nail salons b, h 25 20 0.12 0.6
Pet shops (animal areas) b 10 7.5 0.18 0.9
Supermarkets 8 7.5 0.06 —
Sports and amusement
Bowling alleys (seating areas) 40 10 0.12 —
Disco/dance floors 100 20 0.06 —
Game arcades 20 7.5 0.18 —
Gym, stadium, arena (play area) — — 0.30 —
Heath club/aerobics room 40 20 0.06 —
Health club/weight room 10 20 0.06 —
Ice arenas without combustion engines — — 0.30 0.5
Spectator areas 150 7.5 0.06 —
Swimming pools (pool and deck area) — — 0.48 —
Storage
Repair garages, enclosed parking garages b,d — — — 0.75
Warehouses — — 0.06 —
Theaters
Auditoriums (see education) — — — —
Lobbies 150 5 0.06 —
Stages, studios 70 10 0.06 —
Ticket booths 60 5 0.06 —
Transportation
Platforms 100 7.5 0.06 —
Transportation waiting 100 7.5 0.06 —
Workrooms
Bank vaults/safe deposit 5 5 0.06 —
Computer (without printing) 4 5 0.06 —
Copy, printing rooms 4 5 0.06 0.5
Darkrooms — — — 1.0
Meat processing c 10 15 — —
Pharmacy (prep. area) 10 5 0.18 —
Photo studios 10 5 0.12 —
For SI: 1 cubic foot per minute = 0.0004719 m3/s, 1 ton = 908 kg, 1 cubic foot per minute per square foot = 0.00508 m3/(s • m2), °C = ((°F) - 32) /1.8, 1 square foot = 0.0929 m2.
a. Based upon net occupiable floor area.
b. Mechanical exhaust required and the recirculation of air from such spaces is prohibited (see Section 403.2.1, Item 3).
c. Spaces unheated or maintained below 50°F are not covered by these requirements unless the occupancy is continuous.
d. Ventilation systems in enclosed parking garages shall comply with Section 404.
e. Rates are per water closet or urinal. The higher rate shall be provided where the exhaust system is designed to operate intermittently. The lower rate shall be permitted only where the exhaust system is designed to operate continuously while the space served by the toilet facilities is occupied.
f. Rates are per room unless otherwise indicated. The higher rate shall be provided where the exhaust system is designed to operate intermittently. The lower rate shall be permitted only where the exhaust system is designed to operate continuously while the dwelling unit or sleeping unit served by the toilet facility is occupied.
g. Mechanical exhaust is required and recirculation from such spaces is prohibited (see Section 403.2.1, Item 4).
h. For nail salons, each manicure and pedicure station shall be provided with a source capture system capable of exhausting not less than 50 cfm per station. Exhaust inlets shall be located in accordance with Section 502.20. Where one or more required source capture systems operate continuously during occupancy, the exhaust rate from such systems shall be permitted to be applied to the exhaust flow rate required by Table 403.3.1.1 for the nail salon.
i. For each dwelling unit within R-2 occupancies, outdoor ventilation air shall be provided by mechanical means when the sum of all exhaust air flow rates, whether continuous or intermittent, is designed to exceed 75 cfm. When provided, mechanical ventilation air flow rate shall be approximately equal to the exhaust air flow rate in accordance with Section 403.1 and shall not be less than that required by the air flow rates prescribed in Table 403.3.1.1. For such dwelling units, manually operated openable exterior wall openings shall not be used to provide required mechanical ventilation air.
j. During unoccupied hours the ventilation rate and exhaust rates may be reduced to 0.5 cfm/ft2.
k. When an educational science laboratory is occupied and hoods are not in use and hazardous materials are not present, then ventilation rates shall be consistent with actual use of the space, but not less than 0.5 cfm/ft2.
l. See Section 502.6 for additional requirements.
m. Exception: kitchens and kitchenettes in dwelling units of R-2 occupancy may be naturally ventilated in accordance with Section 402.
(Am. L.L. 2017/187, 10/16/2017, eff. 10/16/2020)
Editor's note: For related unconsolidated provisions, see Appendix A at L.L. 2017/187.
403.3.1.1.1 Zone outdoor airflow.
The minimum outdoor airflow required to be supplied to each zone shall be determined as a function of occupancy classification and space air distribution effectiveness in accordance with Sections 403.3.1.1.1.1 through 403.3.1.1.1.3.
403.3.1.1.1.1 Breathing zone outdoor airflow.
The outdoor airflow rate required in the breathing zone Vbz of the occupiable space or spaces in a zone shall be determined in accordance with Equation 4-1.
Vbz = Rp Pz+ Ra Az (Equation 4-1)
where:
Az = Zone floor area: the net occupiable floor area of the space or spaces in the zone.
Pz = Zone population: the number of people in the space or spaces in the zone.
Rp = People outdoor air rate: the outdoor airflow rate required per person from Table 403.3.1.1.
Ra = Area outdoor air rate: the outdoor airflow rate required per unit area from Table 403.3.1.1.
403.3.1.1.1.2 Zone air distribution effectiveness.
The zone air distribution effectiveness (Ez) shall be determined using Table 403.3.1.1.1.2.
Table 403.3.1.1.1.2
Zone Air Distribution Effectiveness a, b, c, d
Air Distribution Configuration Ez
Ceiling or floor supply of cool air 1.0 e
Ceiling or floor supply of warm air and floor return 1.0
Ceiling supply of warm air and ceiling return 0.8 f
Floor supply of warm air and ceiling return 0.7
Makeup air drawn in on the opposite side of the room from the exhaust and/or return 0.8
Makeup air drawn in near to the exhaust and/or return location 0.5
For SI: 1 foot = 304.8 mm, 1 foot per minute = 0.00506 m/s, °C = ((°F) - 32) /1.8.
a. "Cool air" is air cooler than space temperature.
b. "Warm air" is air warmer than space temperature.
c. "Ceiling" includes any point above the breathing zone.
d. "Floor" includes any point below the breathing zone.
e. Zone air distribution effectiveness of 1.2 shall be permitted for systems with a floor supply of cool air and ceiling return, provided that low-velocity displacement ventilation achieves unidirectional flow and thermal stratification.
f. Zone air distribution effectiveness of 1.0 shall be permitted for systems with a ceiling supply of warm air, provided that supply air temperature is less than 15°F above space temperature and provided that the 150 foot-per-minute supply air jet reaches to within 4 1/2 feet of floor level.
403.3.1.1.1.3 Zone outdoor airflow.
The zone outdoor airflow rate (Voz), shall be determined in accordance with Equation 4-2.
Voz = Vbz / Ez (Equation 4-2)
403.3.1.1.2 System outdoor airflow.
The outdoor air required to be supplied by each ventilation system shall be determined in accordance with Sections 403.3.1.1.2.1 through 403.3.1.1.2.3 as a function of system type and zone outdoor airflow rates.
403.3.1.1.2.1 Single zone systems.
Where one air handler supplies a mixture of outdoor air and recirculated return air to only one zone, the system outdoor air intake flow rate (Vot) shall be determined in accordance with Equation 4-3.
Vot = Voz (Equation 4-3)
403.3.1.1.2.2 100-percent outdoor air systems.
Where one air handler supplies only outdoor air to one or more zones, the system outdoor air intake flow rate (Vot) shall be determined using Equation 4-4.
Vot = Σall zones Voz (Equation 4-4)
403.3.1.1.2.3 Multiple zone recirculating systems.
Where one air handler supplies a mixture of outdoor air and recirculated return air to more than one zone, the system outdoor air intake flow rate (Vot) shall be determined in accordance with Sections 403.3.1.1.2.3.1 through 403.3.1.1.2.3.4.
403.3.1.1.2.3.1 Primary outdoor air fraction.
The primary outdoor air fraction (Zp) shall be determined for each zone in accordance with Equation 4-5.
Zp = Voz / Vpz (Equation 4-5)
where:
Vpz = Primary airflow: The airflow rate supplied to the zone from the air-handling unit at which the outdoor air intake is located. It includes outdoor intake air and recirculated air from that air-handling unit but does not include air transferred or air recirculated to the zone by other means. For design purposes, Vpz shall be the zone design primary airflow rate, except for zones with variable air volume supply and Vpz shall be the lowest expected primary air-flow rate to the zone when it is fully occupied.
403.3.1.1.2.3.2 System ventilation efficiency.
The system ventilation efficiency (Ev) shall be determined using Table 403.3.1.1.2.3.2 or Appendix A of ASHRAE 62.1.
Table 403.3.1.1.2.3.2
System Ventilation Efficiency a, b
Max (ZP) Ev
≤ 0.15 1
≤ 0.25 0.9
≤ 0.35 0.8
≤ 0.45 0.7
≤ 0.55 0.6
≤ 0.65 0.5
≤ 0.75 0.4
> 0.75 0.3
a. Max (Zp) is the largest value of Zp calculated using Equation 4-5 among all the zones served by the system.
b. Interpolating between table values shall be permitted.
403.3.1.1.2.3.3 Uncorrected outdoor air intake.
The uncorrected outdoor air intake flow rate (Vou) shall be determined in accordance with Equation 4-6.
Vou = D Σall zones RpPz + Σall zones RaAz (Equation 4-6)
where:
D = Occupant diversity: the ratio of the system population to the sum of the zone populations, determined in accordance with Equation 4-7.
D = Ps (Equation 4-7)
Σall zones Pz
where:
Ps = System population: The total number of occupants in the area served by the system. For design purposes, Ps shall be the maximum number of occupants expected to be concurrently in all zones served by the system.
403.3.1.1.2.3.4 Outdoor air intake flow rate.
The outdoor air intake flow rate (Vot) shall be determined in accordance with Equation 4-8.
Vot = Vou / Ev (Equation 4-8)
403.3.1.2 Short-term conditions.
If it is known that peak occupancy will be of short duration and/or ventilation will be varied or interrupted for a short period of time, the design may be based on the average conditions over a time period T determined by Equation 4-9.
T = 3V / Vbz (Equation 4-9) (US)
T = 50V / Vbz (Equation 4-9) (SI)
where:
T = averaging time period, minutes
V = the volume of the zone of which averaging is being applied, cubic feet
Vbz = the breathing zone outdoor airflow calculated using equation 4-1 and design valve of the zone population Pz, cfm
Acceptable design adjustments based on this optional provision include the following:
1. Zone with fluctuating occupancy: the zone population (Pz) may be averaged over time T.
2. Zone with intermittent interruption of supply air: the average outdoor airflow supplied to breathing zone over time T shall be no less than the breathing zone outdoor airflow (Vbz) calculated using Equation 4-1.
3. A system with intermittent closure of outdoor air intake: the average outdoor air intake over time T shall be no less than the minimum outdoor air intake (Vot) calculated using Equation 4-3, 4-4 or 4-8 as appropriate.
403.3.1.3 Exhaust ventilation.
Exhaust airflow rate shall be provided in accordance with the requirements of Table 403.3.1.1. Exhaust makeup air shall be permitted to be any combination of outdoor air, recirculated air and transfer air, except as limited in accordance with Section 403.2.
403.3.1.4 System operation.
The minimum flow rate of outdoor air that the ventilation system must be capable of supplying during its operation shall be permitted to be based on the rate per person indicated in Table 403.3.1.1 and the actual number of occupants present.
403.3.1.5 Variable air volume system control.
Variable air volume air distribution systems, other than those designed to supply only 100-percent outdoor air, shall be provided with controls to regulate the flow of outdoor air. Such control system shall be designed to maintain the flow rate of outdoor air at a rate of not less than that required by Section 403.3.1.1 over the entire range of supply air operating rates.
403.3.1.6 Balancing.
The ventilation air distribution system shall be provided with means to adjust the system to achieve not less than the minimum ventilation airflow rate as required by Sections 403.3.1.1 and 403.3.1.2. Ventilation systems shall be balanced by an approved method. Such balancing shall verify that the ventilation system is capable of supplying and exhausting the airflow rates required by Sections 403.3.1.1 and 403.3.1.2.
Source: City of New York, Charter, Administrative Code and Rules (American Legal Publishing XML export, codelibrary.amlegal.com)URL: https://codelibrary.amlegal.com/codes/newyorkcity/latest/NYCadmin/0-0-0-193220Fetched: 10/24/2026