CODES

ADOPTS WITH AMENDMENTS:

International Mechanical Code 2009 (IMC 2009)

Copyright

Preface

Chapter 1 Scope and 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

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. Ambulatory care facilities and Group I-2 occupancies shall be ventilated by mechanical means in accordance with Section 407.
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. Where openings front on a street or public way, the distance shall be measured to the centerline of the street or public way.
  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 501.2.1.
  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 design flood level.

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. Outdoor air intake openings located in exterior walls shall meet the provisions for exterior wall opening protectives in accordance with the 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: The registered design professional may use ASHRAE 62.1 or ASHRAE 62.2, as applicable, as an alternative engineered ventilation system design provided that the registered design professional demonstrates compliance with all applicable sections of the ASHRAE standard.

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, the ventilation rates in Table 403.3 are based on the absence of smoking in occupiable spaces. Where smoking is anticipated in a space other than a smoking lounge, the ventilation system serving the space shall be designed to provide ventilation over and above that required by Table 403.3 in accordance with accepted engineering practice.

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 CLASSIFICATIONPEOPLE OUTDOOR
AIRFLOW RATE IN
BREATHING ZONE, Rp
CFM/PERSON
AREA OUTDOOR
AIRFLOW RATE IN
BREATHING ZONE, Ra
CFM/FT2 a
DEFAULT OCCUPANT
DENSITY #/1000 FT2 a,i
EXHAUST AIRFLOW
RATE CFM/FT2 a
Correctional facilities
Cells
without plumbing fixtures50.1225
with plumbing fixturesg50.12251.0
Dining halls
(see food and beverage service)
Guard stations50.0615
Day room50.0630
Booking/waiting7.50.0650
Dry cleaners, laundries
Coin-operated dry cleaner1520
Coin-operated laundries7.50.0620
Commercial dry cleaner3030
Commercial laundry2510
Storage, pick up7.50.1230
Education
Auditoriums50.06150
Corridors (see public spaces)
Media center100.1225
Sports locker roomsg0.5
Music/theater/dance100.0635
Smoking loungesb6070
Day care (through age 4)100.1825
Classrooms (ages 5-8)100.1225
Classrooms (age 9 plus)100.1235
Lecture classroom7.50.0665
Lecture hall (fixed seats)7.50.06150
Art classroomg100.18200.7
Science laboratoriesg100.18251.0
Wood/metal shopsg100.18200.5
Computer lab100.1225
Multiuse assembly7.50.06100
Locker/dressing roomsg0.25
Food and beverage service
Bars, cocktail lounges7.50.18100
Cafeteria, fast food7.50.18100
Dining rooms7.50.1870
Kitchens (cooking)b0.7
Hotels, motels, resorts and dormitories
Multipurpose assembly50.06120
Bathrooms/toilet—privateg25/50f
Bedroom/living room50.0610
Conference/meeting50.0650
Dormitory sleeping areas50.0620
Gambling casinos7.50.18120
Lobbies/prefunction7.50.0630
Offices
Conference rooms50.0650
Office spaces50.065
Reception areas50.0630
Telephone/data entry50.0660
Main entry lobbies50.0610
Private dwellings, single and multiple
Garages, common for multiple unitsb0.75
Garages, separate for each dwellingb100 cfm per car
Kitchensb25/100f
Living areasc0.35 ACH but not less than 15 cfm/personBased upon number of
bedrooms. First
bedroom, 2; each
additional bedroom, 1
Toilet rooms and bathroomsg20/50f
Public spaces
Corridors0.06
Elevator car1.0
Shower room (per shower head)g50/20f
Smoking loungesb6070
Toilet rooms – publicg50/70e
Places of religious worship50.06120
Courtrooms50.0670
Legislative chambers50.0650
Libraries50.1210
Museums (children’s)7.50.1240
Museums/galleries7.50.0640
Retail stores, sales floors and
showroom floors
Sales (except as below)7.50.1215
Dressing rooms0.25
Mall common areas7.50.0640
Shipping and receiving0.12
Smoking loungesb6070
Storage rooms0.12
Warehouses (see storage)
Specialty shops
Automotive motor-fuel dispensing stationsb1.5
Barber7.50.06250.5
Beauty and nail salonsb, h200.12250.6
Embalming roomb2.0
Pet shops (animal areas)b7.50.18100.9
Supermarkets7.50.068
Sports and amusement
Disco/dance floors200.06100
Bowling alleys (seating areas)100.1240
Game arcades7.50.1820
Ice arenas without combustion engines0.300.5
Gym, stadium, arena (play area)0.30
Spectator areas7.50.06150
Swimming pools (pool and deck area)0.48
Health club/aerobics room200.0640
Health club/weight room200.0610
Storage
Repair garages, enclosed parking garagesb,d0.75
Warehouses0.06
Theaters
Auditoriums (see education)
Lobbies50.06150
Stages, studios100.0670
Ticket booths50.0660
Transportation
Platforms7.50.06100
Transportation waiting7.50.06100
Workrooms
Bank vaults/safe deposit50.065
Darkrooms1.0
Copy, printing rooms50.0640.5
Meat processingc1510
Pharmacy (prep. area)50.1810
Photo studios50.1210
Computer (without printing)50.064

For SI: 1 cubic foot per minute = 0.0004719 m3/s, 1 ton = 908 kg, 1 cubic foot per minute per square foot = 0.00508m3/(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 periods of heavy use are expected to occur, such as toilets in theaters, schools and sports facilities. The lower rate shall be permitted where periods of heavy use are not expected.
  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 where the exhaust system is designed to operate continuously during normal hours of use.
  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, the required exhaust shall include ventilation tables or other systems that capture the contaminants and odors at their source and are capable of exhausting a minimum of 50 cfm per station.
  9. The occupant load shall not be greater than that determined by Section 1004 of the building code.
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 foot-per-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 where the system is arranged to operate automatically upon detection of vehicle operation or the presence of occupants by approved automatic detection devices.
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 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.

Mechanical ventilation for ambulatory care facilities and Group I-2 occupancies shall be designed and installed in accordance with this code and ASHRAE 170.

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