CODES

ADOPTS WITH AMENDMENTS:

International Mechanical Code 2012 (IMC 2012)

Copyright

Preface

Chapter 1 Administration

Chapter 2 Definitions

Chapter 3 General Regulations

Chapter 4 Ventilation

Chapter 5 Exhaust Systems

Chapter 6 Duct Systems

Chapter 7 Combustion Air

Chapter 8 Chimneys and Vents

Chapter 9 Specific Appliances, Fireplaces and Solid Fuel-Burning Equipment

Chapter 10 Boilers, Water Heaters and Pressure Vessels

Chapter 11 Refrigeration

Chapter 12 Hydronic Piping

Chapter 13 Fuel Oil Piping and Storage

Chapter 14 Solar Systems

Chapter 15 Referenced Standards

Appendix A Chimney Connector Pass-Throughs

Appendix B Recommended Permit Fee Schedule

This chapter shall govern the ventilation of spaces within a building intended to be occupied. Mechanical exhaust systems, including exhaust systems serving clothes dryers and cooking appliances; hazardous exhaust systems; dust, stock and refuse conveyor systems; subslab soil exhaust systems; smoke control systems; energy recovery ventilation systems and other systems specified in Section 502 shall comply with Chapter 5.
Every occupied space shall be ventilated by natural means in accordance with Section 402 or by mechanical means in accordance with Section 403. Where the air infiltration rate in a dwelling unit is less than 5 air changes per hour when tested with a blower door at a pressure of 0.2-inch water column (50 Pa) in accordance with Section R402.4.1.2 of the International Energy Conservation Code, the dwelling unit shall be ventilated by mechanical means in accordance with Section 403.
Ventilation shall be provided during the periods that the room or space is occupied.

Air intake openings shall comply with all of the following:

  1. Intake openings shall be located a minimum of 10 feet (3048 mm) from lot lines or buildings on the same lot.
  2. Mechanical and gravity outdoor air intake openings shall be located not less than 10 feet (3048 mm) horizontally from any hazardous or noxious contaminant source, such as vents, streets, alleys, parking lots and loading docks, except as specified in Item 3 or Section 501.3.1. Outdoor air intake openings shall be permitted to be located less than 10 feet (3048 mm) horizontally from streets, alleys, parking lots and loading docks provided that the openings are located not less than 25 feet (7620 mm) vertically above such locations. Where openings front on a street or public way, the distance shall be measured from the closest edge of the street or public way.
  3. Intake openings shall be located not less than 3 feet (914 mm) below contaminant sources where such sources are located within 10 feet (3048 mm) of the opening.
  4. Intake openings on structures in flood hazard areas shall be at or above the elevation required by Section 1612 of the International Building Code for utilities and attendant equipment.

Air intake openings that terminate outdoors shall be protected with corrosion-resistant screens, louvers or grilles. Openings in louvers, grilles and screens shall be sized in accordance with Table 401.5, and shall be protected against local weather conditions. Louvers that protect air intake openings in structures located in hurricane-prone regions, as defined in the International Building Code, shall comply with AMCA 550. Outdoor air intake openings located in exterior walls shall meet the provisions for exterior wall opening protectives in accordance with the International Building Code.

TABLE 401.5

OPENING SIZES IN LOUVERS, GRILLES AND SCREENS PROTECTING AIR INTAKE OPENINGS

OUTDOOR OPENING TYPEMINIMUM AND MAXIMUM OPENING
SIZES IN LOUVERS, GRILLES AND
SCREENS MEASURED IN ANY
DIRECTION
Intake openings in
residential occupancies
Not < 1/4 inch and not > 1/2 inch
Intake openings in other
than residential occupancies
> 1/4 inch and not > 1 inch

For SI: 1 inch = 25.4 mm.

Stationary local sources producing airborne particulates, heat, odors, fumes, spray, vapors, smoke or gases in such quantities as to be irritating or injurious to health shall be provided with an exhaust system in accordance with Chapter 5 or a means of collection and removal of the contaminants. Such exhaust shall discharge directly to an approved location at the exterior of the building.

Natural ventilation of an occupied space shall be through windows, doors, louvers or other openings to the outdoors. The operating mechanism for such openings shall be provided with ready access so that the openings are readily controllable by the building occupants.
The minimum openable area to the outdoors shall be 4 percent of the floor area being ventilated.

Where rooms and spaces without openings to the outdoors are ventilated through an adjoining room, the opening to the adjoining rooms shall be unobstructed and shall have an area not less than 8 percent of the floor area of the interior room or space, but not less than 25 square feet (2.3 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.

Exception: Exterior openings required for ventilation shall be permitted to open into a thermally isolated sunroom addition or patio cover, provided that the openable area between the sunroom addition or patio cover and the interior room has an area of not less than 8 percent of the floor area of the interior room or space, but not less than 20 square feet (1.86 m2). The minimum openable area to the outdoors shall be based on the total floor area being ventilated.

Where openings below grade provide required natural ventilation, the outside horizontal clear space measured perpendicular to the opening shall be one and one-half times the depth of the opening. The depth of the opening shall be measured from the average adjoining ground level to the bottom of the opening.
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. The system to convey ventilation air shall be designed and installed in accordance with Chapter 6.

The minimum outdoor airflow rate shall be determined in accordance with Section 403.3. Ventilation supply systems shall be designed to deliver the required rate of outdoor airflow to the breathing zone within each occupiable space.

Exception: Where the registered design professional demonstrates that an engineered ventilation system design will prevent the maximum concentration of contaminants from exceeding that obtainable by the rate of outdoor air ventilation determined in accordance with Section 403.3, the minimum required rate of outdoor air shall be reduced in accordance with such engineered system design.

The outdoor air required by Section 403.3 shall not be recirculated. Air in excess of that required by Section 403.3 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 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 spaces where more than 10 percent of the resulting supply airstream consists of air recirculated from these spaces.
  3. Where mechanical exhaust is required by Note b in Table 403.3, recirculation of air from such spaces shall be prohibited. All air supplied to such spaces shall be exhausted, including any air in excess of that required by Table 403.3.
  4. Where mechanical exhaust is required by Note g in Table 403.3, mechanical exhaust is required and recirculation is prohibited where more than 10 percent of the resulting supply airstream consists of air recirculated from these spaces.
Except where recirculation from such spaces is prohibited by Table 403.3, 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. The required outdoor airflow rates specified in Table 403.3 shall be introduced directly into such spaces or into the occupied spaces from which air is transferred or a combination of both.

Ventilation systems shall be designed to have the capacity to supply the minimum outdoor airflow rate determined in accordance with this section. The occupant load utilized for design of the ventilation system shall not be less than the number determined from the estimated maximum occupant load rate indicated in Table 403.3. Ventilation rates for occupancies not represented in Table 403.3 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 smoking lounges and other designated areas where smoking is permitted, the ventilation rates in Table 403.3 are based on the absence of smoking in occupiable spaces.

Exception: The occupant load is not required to be determined based on the estimated maximum occupant load rate indicated in Table 403.3 where approved statistical data document the accuracy of an alternate anticipated occupant density.

TABLE 403.3

MINIMUM VENTILATION RATES

OCCUPANCY CLASSIFICATIONOCCUPANT DENSITY
#/1000 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
Cells
without plumbing fixtures2550.12
with plumbing fixturesg2550.121.0
Dining halls
(see food and beverage service)
Guard stations1550.06
Day room3050.06
Booking/waiting507.50.06
Dry cleaners, laundries
Coin-operated dry cleaner2015
Coin-operated laundries207.50.06
Commercial dry cleaner3030
Commercial laundry1025
Storage, pick up307.50.12
Education
Auditoriums15050.06
Corridors (see public spaces)
Media center25100.12
Sports locker roomsg0.5
Music/theater/dance35100.06
Smoking loungesb7060
Day care (through age 4)25100.18
Classrooms (ages 5-8)25100.12
Classrooms (age 9 plus)35100.12
Lecture classroom657.50.06
Lecture hall (fixed seats)1507.50.06
Art classroomg20100.180.7
Science laboratoriesg25100.181.0
Wood/metal shopsg20100.180.5
Computer lab25100.12
Multiuse assembly1007.50.06
Locker/dressing roomsg0.25
Food and beverage service
Bars, cocktail lounges1007.50.18
Bars or cocktail lounges designated as
an area where smoking is permittedb
10030
Cafeteria, fast food1007.50.18
Cafeteria or fast food designated as an
area where smoking is permittedb
10020
Dining rooms707.50.18
Dining rooms designated as an area
where smoking is permittedb
7020
Kitchens (cooking)b0.7
Hospitals, nursing and convalescent homes
Autopsy roomsb0.5
Medical procedure rooms2015
Operating rooms2030
Patient rooms1025
Physical therapy2015
Recovery and ICU2015
Hotels, motels, resorts and dormitories
Multipurpose assembly12050.06
Bathrooms/toilet—privateg25/50f
Bedroom/living room1050.06
Conference/meeting5050.06
Dormitory sleeping areas2050.06
Gambling casinos1207.50.18
Lobbies/prefunction307.50.06
Offices
Conference rooms5050.06
Office spaces550.06
Reception areas3050.06
Telephone/data entry6050.06
Main entry lobbies1050.06
Private dwellings, single and multiple
Garages, common for multiple unitsb0.75
Garages, separate for each dwellingb100 cfm per car
Kitchensb25/100f
Living areascBased upon number of
bedrooms. First bedroom, 2;
each additional bedroom, 1
0.35 ACH but not less
than 15 cfm/person
Toilet rooms and bathroomsg20/50f
Public spaces
Corridors0.06
Elevator car1.0
Shower room (per shower head)g50/20f
Smoking loungesb7060
Toilet rooms — publicg50/70e
Places of religious worship12050.06
Courtrooms7050.06
Legislative chambers5050.06
Libraries1050.12
Lounges designated as an area
where smoking is permittedb
10030
Museums (children’s)407.50.12
Museums/galleries407.50.06
Retail stores, sales floors and showroom floors
Sales (except as below)157.50.12
Dressing rooms0.25
Mall common areas407.50.06
Shipping and receiving0.12
Smoking loungesb7060
Storage rooms0.12
Warehouses (see storage)
Specialty shops
Automotive motor-fuel dispensing stationsb1.5
Barber257.50.060.5
Beauty salonsb25200.120.6
Nail salonsb, h25200.120.6
Embalming roomb2.0
Pet shops (animal areas)b107.50.180.9
Supermarkets87.50.06
Sports and amusement
Disco/dance floors100200.06
Bowling alleys (seating areas)40100.12
Game arcades207.50.18
Ice arenas without combustion engines0.300.5
Gym, stadium, arena (play area)0.30
Spectator areas1507.50.06
Swimming pools (pool and deck area)0.48
Health club/aerobics room40200.06
Health club/weight room10200.06
Storage
Repair garages, enclosed parking garagesb, d0.75
Warehouses0.06
Theaters
Auditoriums (see education)
Lobbies15050.06
Stages, studios70100.06
Ticket booths6050.06
Transportation
Platforms1007.50.06
Transportation waiting1007.50.06
Workrooms
Bank vaults/safe deposit550.06
Darkrooms1.0
Copy, printing rooms450.060.5
Meat processingc1015
Pharmacy (prep. area)1050.18
Photo studios1050.12
Computer (without printing)450.06

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.

  1. Based upon net occupiable floor area.
  2. Mechanical exhaust required and the recirculation of air from such spaces is prohibited (see Section 403.2.1, Item 3).
  3. Spaces unheated or maintained below 50°F are not covered by these requirements unless the occupancy is continuous.
  4. Ventilation systems in enclosed parking garages shall comply with Section 404.
  5. 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 occupied.
  6. 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 occupied.
  7. Mechanical exhaust is required and recirculation is prohibited except that recirculation shall be permitted where the resulting supply airstream consists of not more than 10 percent air recirculated from these spaces (see Section 403.2.1, Items 2 and 4).
  8. For nail salons, each nail station shall be provided with a source capture system capable of exhausting not less than 50 cfm per station.
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 through 403.3.1.3.

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.

(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.
Ra=Area outdoor air rate: the outdoor airflow rate required per unit area from Table 403.3.

The zone air distribution effectiveness (Ez) shall be determined using Table 403.3.1.2.

TABLE 403.3.1.2

ZONE AIR DISTRIBUTION EFFECTIVENESSa,b,c,d,e

AIR DISTRIBUTION CONFIGURATIONEz
Ceiling or floor supply of cool air1.0f
Ceiling or floor supply of warm air and floor return1.0
Ceiling supply of warm air and ceiling return0.8g
Floor supply of warm air and ceiling return0.7
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.

  1. “Cool air” is air cooler than space temperature.
  2. “Warm air” is air warmer than space temperature.
  3. “Ceiling” includes any point above the breathing zone.
  4. “Floor” includes any point below the breathing zone.
  5. “Makeup air” is air supplied or transferred to a zone to replace air removed from the zone by exhaust or return systems.
  6. 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.
  7. 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 footper-minute supply air jet reaches to within 41/2 feet of floor level.

The zone outdoor airflow rate (Voz), shall be determined in accordance with Equation 4-2.

(Equation 4-2)

The outdoor air required to be supplied by each ventilation system shall be determined in accordance with Sections 403.3.2.1 through 403.3.2.3 as a function of system type and zone outdoor airflow rates.

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.

(Equation 4-3)

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.

(Equation 4-4)

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 403.3.2.3.1 through 403.3.2.3.4.

The primary outdoor air fraction (Zp) shall be determined for each zone in accordance with Equation 4-5.

(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 airflow rate to the zone when it is fully occupied.

The system ventilation efficiency (Ev) shall be determined using Table 403.3.2.3.2 or Appendix A of ASHRAE 62.1.

TABLE 403.3.2.3.2

SYSTEM VENTILATION EFFICIENCYa,b

Max (Zp)Ev
≤ 0.151
≤ 0.250.9
≤ 0.350.8
≤ 0.450.7
≤ 0.550.6
≤ 0.650.5
≤ 0.750.4
> 0.750.3
  1. Max (Zp) is the largest value of Zp calculated using Equation 4-5 among all the zones served by the system.
  2. Interpolating between table values shall be permitted.

The uncorrected outdoor air intake flow rate (Vou) shall be determined in accordance with Equation 4-6.

(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.

(Equation 4-7)

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.

The outdoor air intake flow rate (Vot) shall be determined in accordance with Equation 4-8.

(Equation 4-8)

Exhaust airflow rate shall be provided in accordance with the requirements in Table 403.3. 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.
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 and the actual number of occupants present.
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 over the entire range of supply air operating rates.
The ventilation air distribution system shall be provided with means to adjust the system to achieve at least the minimum ventilation airflow rate as required by Sections 403.3 and 403.4. 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 and 403.4.

Mechanical ventilation systems for enclosed parking garages shall be permitted to operate intermittently in accordance with Item 1, Item 2 or both.

  1. The system shall be arranged to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.
  2. The system shall be arranged to operate automatically by means of carbon monoxide detectors applied in conjunction with nitrogen dioxide detectors. Such detectors shall be installed in accordance with their manufacturers’ recommendations.
Automatic operation of the system shall not reduce the ventilation airflow rate below 0.05 cfm per square foot (0.00025 m3/s • m2) of the floor area and the system shall be capable of producing a ventilation airflow rate of 0.75 cfm per square foot (0.0038 m3/s • m2) of floor area.
Connecting offices, waiting rooms, ticket booths and similar uses that are accessory to a public garage shall be maintained at a positive pressure and shall be provided with ventilation in accordance with Section 403.3.
Mechanical ventilation systems shall be provided with manual or automatic controls that will operate such systems whenever the spaces are occupied. Air-conditioning systems that supply required ventilation air shall be provided with controls designed to automatically maintain the required outdoor air supply rate during occupancy.
Uninhabited spaces, such as crawl spaces and attics, shall be provided with natural ventilation openings as required by the International Building Code or shall be provided with a mechanical exhaust and supply air system. The mechanical exhaust rate shall be not less than 0.02 cfm per square foot (0.00001 m3/s • m2) of horizontal area and shall be automatically controlled to operate when the relative humidity in the space served exceeds 60 percent.
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