ADOPTS WITH AMENDMENTS:

International Mechanical Code 2018 (IMC 2018)

Heads up: There are no amended sections in this chapter.
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, other than enclosed parking garages and buildings used for repair of automobiles, shall be ventilated in accordance with Section 401.2.1, 401.2.2 or 401.2.3. Enclosed parking garages and buildings used for the repair of automobiles shall be ventilated by mechanical means in accordance with Sections 403 and 404.
Ventilation in Group R occupancies shall be provided in accordance with Section 403.4.
Ambulatory care facilities and Group I-2 occupancies shall be ventilated by mechanical means in accordance with Section 407.
Ventilation in all other occupancies shall be provided by natural means in accordance with Section 402 or by mechanical means in accordance with Sections 403.1 to 403.7.
Group R occupancies shall be vented continuously or intermittently in accordance with Section 403.4. Ventilation in all other occupancies 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 not less than 10 feet (3048 mm) from lot lines or buildings on the same lot. Lot lines shall not be defined as a separation from a 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 501.3.1. 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.

    Exception: Separation is not required between intake air openings and living space environmental air exhaust air openings of an individual dwelling unit or sleeping unit where a factory-built intake/exhaust combination termination fitting is used to separate the air streams in accordance with the manufacturer's instructions. A minimum 3 feet (914 mm) of separation shall be maintained between other environmental air exhaust outlets and other dwelling or sleeping unit factory-built intake/exhaust combination termination fittings.

  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.

    Exception: Enclosed parking garage and repair garage ventilation air intakes are permitted to be located less than 10 feet (3048 mm) horizontally from or 25 feet (7620 mm) vertically above a street, alley, parking lot, and loading dock.

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 TYPE MINIMUM AND MAXIMUM
OPENING SIZES IN LOUVERS,
GRILLES AND SCREENSa
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.

  1. For rectangular openings, the table requirements apply to the shortest side. For round openings, the table requirements apply to the diameter. For square openings, the table requirements apply to any side.
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.
At the discretion of the building official, flow testing may be required to verify that the mechanical system(s) satisfies the requirements of this chapter. Flow testing may be performed using flow hood measuring at the intake or exhaust points of the system, in-line pitot tube- or pitot-traverse type measurement systems in the duct, short-term tracer gas measurements, or other means approved by the building official.
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 outdoor 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.

Exceptions:

  1. 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.
  2. Alternate systems designed in accordance with ASHRAE Standard 62.1 Section 6.2, Ventilation Rate Procedure, shall be permitted.

The 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 403.3.1.1, 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 from such spaces is prohibited where more than 10 percent of the resulting supply airstream consists of air recirculated from these spaces. Return air from such spaces shall only be permitted to be recirculated when returned to an energy recovery ventilation system complying with Section 514. Recirculation of air that is contained completely within such spaces shall not be prohibited.
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.
Group R occupancies shall be provided with outdoor air and local exhaust in accordance with Section 403.4. All other buildings intended to be occupied shall be provided with outdoor air and local exhaust in accordance with Section 403.3.1.
The design of local exhaust systems and ventilation systems for outdoor air for occupancies other than Group R-2, R-3 and R-4 three stories and less above grade plane shall comply with Sections 403.3.1.1 through 403.3.1.5.

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, the ventilation system shall be designed to deliver the required rate of outdoor airflow to the breathing zone. Outdoor air shall be supplied directly to each occupiable space from an air handling unit through a fully ducted path or ducted to within 12 inches (305 mm) of the return air opening of a fan-powered terminal unit used to transfer the outdoor air to the occupiable space. 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, including transfer fan-powered terminal units 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 403.3.1.1 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 403.3.1.1 in accordance with accepted engineering practice.

Exception: Where occupancy density is known and documented in the plans, the outside air rate may be based on the design occupant density. Under no circumstance shall the occupancies used result in outside air less than one-half that resulting from application of Table 403.3.1.1 estimated maximum occupancy rates.

TABLE 403.3.1.1

REQUIRED OUTDOOR VENTILATION AIR

OCCUPANCY CLASSIFICATION OCCUPANT 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
       
Booking/waiting 50 7.5 0.06
Cells        
without plumbing fixtures 25 5 0.12
with plumbing fixturesg 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 0.12
Commercial dry cleaner 30 30
Commercial laundry 10 25
Storage, pick up 30 7.5 0.12
Education        
Art classroomg 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 roomsg 0.25
Media center 25 10 0.12
Multiuse assembly 100 7.5 0.06
Music/theater/dance 35 10 0.06
Science laboratoriesg 25 10 0.18 1.0
Smoking loungesb 70 60
Sports locker roomsg 0.5
Wood/metal shopsg 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 20 7.5 0.12 0.7
Hotels, motels, resorts and dormitories        
Bathrooms/toilet—privateg 25/50f
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
Offices        
Conference rooms 50 5 0.06
Kitchenettesk 25 5 0.06 0.30
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 unitsb 0.75
Kitchensb See Table 403.4.7
Living areasc See Table 403.4.2
Toilet rooms and bathroomsg See Table 403.4.7
Public spaces        
Corridors serving other than Group R 0.06
Corridors serving Group R dwelling or
sleeping units with whole-house exhaust
system
0.12
Corridors serving Group R dwelling or
sleeping units with other than whole-house
exhaust system
0.06
Courtrooms 70 5 0.06
Elevator car 1.0
Elevator lobbies in parking garage 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 50/20f
Smoking loungesb 70 60
Toilet rooms — publicg 50/70e
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 2 10 0.12
Smoking loungesb 70 60
Storage rooms 0.12
Warehouses (see "Storage") 10 0.06
Specialty shops        
Automotive motor-fuel dispensing stationsb 1.5
Barber 25 7.5 0.06 0.5
Beauty salonsb 25 20 0.12 0.6
Nail salons b, h 25 20 0.12 0.6
Embalming roomb 2.0
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
Health 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        
Janitor closets, trash rooms, recycling rooms       1.0
Repair garages, enclosed parking garagesb,d 0.75
Storage rooms, chemical 1.5
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
Freezer and refrigerated spaces (<50°F) 0 10 0 0
Meat processingc 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.

  1. Based on net occupiable floor area.
  2. Mechanical exhaust required and the recirculation of air from such spaces is prohibited. Recirculation of air that is contained completely within such spaces shall not be 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 from such spaces 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. Return air from such spaces shall only be permitted to be recirculated when returned to an energy recovery ventilation system complying with Section 514. Recirculation of air that is contained completely within such spaces shall not be prohibited (see Section 403.2.1, Items 2 and 4).
  8. 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.
  9. A laundry area within a kitchen or bathroom is not required to have local exhaust. For the laundry area to qualify as being within the kitchen, the laundry room door must open directly into the kitchen and not into an adjacent corridor. Where there are doors that separate the laundry area from the kitchen or bathroom the door shall be louvered.
  10. When combustion equipment is intended to be used on the playing surface, additional dilution ventilation and/or source control shall be provided.
  11. Kitchenettes require exhaust when they contain a domestic cooking appliance range or oven that is installed in accordance with Table 507.2.1. Kitchenettes that only contain a microwave cooking appliance are not required to have exhaust. A kitchenette may not contain commercial cooking appliances that require Type I or Type II exhaust as these occupancies are required to be exhausted to the kitchen category in Table 403.3.1.1
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.

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 403.3.1.1.

Ra = Area outdoor air rate: the outdoor airflow rate required per unit area from Table 403.3.1.1.

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 EFFECTIVENESSa, b, c, d

AIR DISTRIBUTION CONFIGURATION Ez
Ceiling or floor supply of cool air 1.0e
Ceiling or floor supply of warm air and floor return 1.0
Ceiling supply of warm air and ceiling return 0.8f
Floor supply of warm air and ceiling return 0.7
Makeup air drawn in on the opposite side of the room from the exhaust or return 0.8
Makeup air drawn in near to the exhaust 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. 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.
  6. 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 403.3.1.1.2.1 through 403.3.1.1.2.3.4 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)
For ventilation systems wherein one or more air handler supplies a mixture of outdoor air and recirculated return air to more than one ventilation zone, the 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.

The uncorrected outdoor air intake flow (Vot) shall be determined in accordance with Equation 4-5.


(Equation 4-5)

The occupant diversity ratio (D) shall be determined in accordance with Equation 4-6 to account for variations in population within the ventilation zones served by the system.


(Equation 4-6)

where:

Ps = System population: The total population in the area served by the system.

Exception: Alternative methods to account for occupant diversity shall be permitted, provided the resulting Vou value is no less than that determined using Equation 4-5.

Design system population (Ps) shall equal the largest (peak) number of people expected to occupy all ventilation zones served by the ventilation system during use.

Note: Design system population is always equal to or less than the sum of design zone population for all zones in the area served by the system because all zones may or may not be simultaneously occupied at design population.

The system ventilation efficiency (Ev) shall be determined in accordance with Section 403.3.1.1.2.3.3 for the Simplified Procedure or Appendix A of ASHRAE 62.1 for the Alternative Procedure.

Note: These procedures also establish zone minimum primary airflow rates for VAV systems.

TABLE 403.3.1.1.2.3.2

SYSTEM VENTILATION EFFICIENCYa,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
  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.

System ventilation efficiency (Ev) shall be determined in accordance with Equation 4-6a or 4-6b.


(Equation 4-6a)

(Equation 4-6b)

For each zone, the minimum primary airflow (Vpz-min) shall be determined in accordance with Equation 4-7.


(Equation 4-7)

The design 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 of Table 403.3.1.1. Outdoor air introduced into a space by an exhaust system shall be considered as contributing to the outdoor airflow required by Table 403.3.1.1.
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.
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 not less than the minimum ventilation airflow rate as required by Sections 403.3 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 and 403.3.1.2.

This section is not adopted. See Section 403.4.

This section is not adopted.
This section is not adopted.
This section is not adopted.
Where provided within a dwelling unit, controls for outdoor air ventilation systems shall include text or a symbol indicating the system's function.
Exhaust equipment serving single dwelling units shall be listed and labeled to provide the minimum required airflow in accordance with ANSI/AMCA 210-ANSI/ASHRAE 51.
Each dwelling unit or sleeping unit shall be equipped with a whole-house mechanical ventilation system that complies with Sections 403.4.1 through 403.4.6. Each dwelling unit or sleeping unit shall be equipped with local exhaust complying with Section 403.4.7. All occupied spaces, including public corridors, other than the Group R dwelling units and/or sleeping units, that support these Group R occupancies, shall meet the ventilation requirements of Section 402 or the mechanical ventilation requirements of Sections 403.1 through 403.3.
The whole-house ventilation system shall consist of one or more supply fans, one or more exhaust fans, or an ERV/HRV with integral fans; and the associated ducts and controls. Local exhaust fans shall be permitted to serve as part of the whole-house ventilation system when provided with the proper controls in accordance with Section 403.4.5. The systems shall be designed and installed to supply and exhaust the minimum outdoor airflow rates per Section 403.4.2 as corrected by the balanced and/or distributed whole-house ventilation system coefficients in accordance with Section 403.4.3 where applicable.

The sleeping unit whole-house mechanical ventilation minimum outdoor airflow rate shall be determined in accordance with the breathing zone ventilation rates. Minimum outdoor airflow rate shall be determined in accordance with the breathing zone ventilation rate requirements of Section 403.3.1.1.1.2 using Equation 4-2. The dwelling unit whole-house mechanical ventilation minimum outdoor airflow rate shall be determined in accordance with Equation 4-10 or Table 403.4.2.


(Equation 4-10)

where:

Qr = Ventilation airflow rate, cubic feet per minute (cfm) (m3/min) but not less than 30 cfm (0.85 m3/min) for each dwelling unit.

Afloor = Conditioned floor area, square feet (ft2) (m2).

Nbr = Number of bedrooms, not less than one.


(Equation 4-11)

where:

Qv = Quality-adjusted ventilation airflow rate in cubic feet per minute (cfm) (m3/min).

Qr = Ventilation airflow rate, cubic feet per minute (cfm) (m3/min) from Equation 4-10 or Table 403.4.1.

Csystem= System coefficient from Table 403.4.2.

TABLE 403.4.2

WHOLE-HOUSE MECHANICAL VENTILATION AIRFLOW RATE (CONTINUOUSLY OPERATING SYSTEMS)

FLOOR AREA (ft2) BEDROOMSa
1 2 3 4 >5
<500 30 30 35 45 50
500 - 1000 30 35 40 50 55
1001 - 1500 30 40 45 55 60
1501 - 2000 35 45 50 60 65
2001 - 2500 40 50 55 65 70
2501 - 3000 45 55 60 70 75
3001 - 3500 50 60 65 75 80
3501 - 4000 55 65 70 80 85
4001 - 4500 60 70 75 85 90
4501 - 5000 65 75 80 90 95

For SI: 1 square foot = 0.092903 m2 , 1 cubic foot per minute = 0.03 m3/min.

  1. Minimum airflow (Qr) is set at not less than 30 cfm for each dwelling unit.

The minimum whole-house ventilation rate from Section 403.4.2 shall be adjusted by the system coefficient in Table 403.4.3 based on the system type not meeting the definition of a balanced whole-house ventilation system and/or not meeting the definition of a distributed whole-house ventilation system.

TABLE 403.4.3

SYSTEM COEFFICIENT (Csystem)

SYSTEM TYPE DISTRIBUTED NOT DISTRIBUTED
Balanced 1.0 1.25
Not Balanced 1.25 1.5
Residential dwelling and sleeping unit whole-house ventilation systems shall meet the requirements of Section 403.4.4.1 or 403.4.4.2 depending on the occupancy of the residential unit.
Residential dwelling and sleeping units in Group R-2 occupancies system shall include supply and exhaust fans and be a balanced whole-house ventilation system in accordance with Section 403.4.6.3. The system shall include a heat or energy recovery ventilator with a sensible heat recovery effectiveness as prescribed in Section C403.3.6 of the Washington State Energy Code. The whole-house ventilation system shall operate continuously at the minimum ventilation rate determined in accordance with Section 403.4. The whole-house supply fan shall provide ducted outdoor ventilation air to each habitable space within the residential unit.
Residential dwelling and sleeping units in other than Group R-2 occupancies, including I-1, condition 2 occupancies, shall have a whole-house mechanical ventilation system with supply and exhaust fans in accordance with Section 403.4.6.1, 403.4.6.2, 403.4.6.3, or 403.4.6.4. The whole-house ventilation system shall operate continuously at the minimum ventilation rate determined in accordance with Section 403.4.2 unless configured with intermittent off controls in accordance with Section 403.4.6.5. The whole-house supply fan shall provide ducted outdoor ventilation air to each habitable space within the residential unit.

Controls for the whole-house ventilation system shall comply with the following:

  1. The whole-house ventilation system shall be controlled with manual switches, timers or other means that provide for automatic operation of the ventilation system that have ready access for the occupant.
  2. The whole-house mechanical ventilation system shall be provided with controls that enable manual override off of the system by the occupant during periods of poor outdoor air quality. Controls shall include permanent text or a symbol indicating their function. Recommended control permanent labeling to include text similar to the following: "Leave on unless outdoor air quality is very poor." Manual controls shall have ready access for the occupant.

    Exception: Central whole-house mechanical systems with supply air and/or exhaust that serves more than one dwelling or sleeping unit are not required to have manual override off controls accessible by the occupant.

  3. Whole-house ventilation systems shall be configured to operate continuously except where intermittent off controls are provided in accordance with Section 403.4.6.5 and allowed by Section 403.4.4.2.

Whole-house ventilation supply and exhaust fans specified in this section shall have a minimum efficacy as prescribed in the Washington State Energy Code. The fans shall be rated for sound at a maximum of 1.0 sone at design airflow and static pressure conditions. Design and installation of the system or equipment shall be carried out in accordance with manufacturer's installation instructions.

Exceptions:

  1. Central supply or exhaust fans serving multiple residential units do not need to comply with the maximum fan sone requirements.
  2. Interior joining spaces provided with a 30-cfm (0.85 m3/min) transfer fan or a 25-square-foot (2.3 m2) permanent opening do not require supply ventilation air directly to the space. Transfer fans shall meet the sone rating above and have whole-house ventilation controls in accordance with Section 403.4.5.

Exhaust fans required shall be ducted directly to the outside in accordance with Section 501.3. Exhaust air outlets shall be designed to limit the pressure difference to the outside to limiting the outlet free area maximum velocity to 500 feet per minute (152 m/min) and equipped with backdraft dampers or motorized dampers in accordance with the Washington State Energy Code. Exhaust fans shall be tested and rated in accordance with HVI 915, HVI 916, and HVI 920. Exhaust fans required in this section may be used to provide local ventilation. Exhaust fans that are designed for intermittent exhaust airflow rates higher than the continuous exhaust airflow rates in Table 403.4.3 shall be provided with occupancy sensors or humidity sensors to automatically override the fan to the high-speed airflow rate. The exhaust fans shall be tested and the testing results shall be submitted and posted in accordance with Section 403.4.6.7.

Exception: Central exhaust fans serving multiple residential units do not need to comply with the HVI testing requirements.

Supply fans used in meeting the requirements of this section shall supply outdoor air from intake openings in accordance with Sections 401.4 and 401.5. Intake air openings shall be designed to limit the pressure difference to the outside to limiting the inlet free area maximum velocity to 500 feet per minute (152 m/min) and when designed for intermittent off operation shall be equipped with motorized dampers in accordance with the Washington State Energy Code. Supply fans shall be tested and rated in accordance with HVI 915, HVI 916, and HVI 920. Where outdoor air is provided to each habitable dwelling unit or sleeping unit by supply fan systems the outdoor air shall be filtered. The filter shall be provided with access for regular maintenance and replacement. The filter shall have a Minimum Efficiency Rating Value (MERV) of at least 8.

Exception: Central supply fans serving multiple residential units do not need to comply with the HVI testing requirements

A balanced whole-house ventilation system shall include both supply and exhaust fans. The supply and exhaust fans shall have airflow that is within 10 percent of each other. The tested and balanced total mechanical exhaust airflow rate is within 10 percent or 5 cfm, whichever is greater, of the total mechanical supply airflow rate. The flow rate test results shall be submitted and posted in accordance with Section 403.4.6.6. The exhaust fan shall meet the requirements of Section 403.4.6.2. The supply fan shall meet the requirements of Section 403.4.6.3. For R-2 dwelling and sleeping units, the system is required to have balanced whole-house ventilation but is not required to have distributed whole-house ventilation where the not distributed system coefficient from Table 403.4.3 is utilized to correct the whole-house mechanical ventilation rate. The system shall be designed and balanced to meet the pressure equalization requirements of Section 501.4. Intermittent dryer exhaust, intermittent range hood exhaust, and intermittent toilet room exhaust airflow rates above the residential dwelling or sleeping unit minimum ventilation rate are exempt from the balanced airflow calculation.

Systems using space condition heating and/or cooling air handler fans for outdoor air supply air distribution are not permitted.

Exception: Air handler fans shall be permitted that have multi-speed or variable speed supply airflow control capability with a low-speed operation not greater than 25 percent of the rated supply airflow capacity during ventilation-only operation. Outdoor air intake openings must meet the provisions of Sections 401.4 and 401.5 and must include a motorized damper that is activated by the whole-house ventilation system controller. Intake air openings shall be designed to limit the pressure difference to the outside to limiting the inlet free area maximum velocity to 500 ft per min (152 m/min). The motorized damper must be controlled to maintain the outdoor airflow intake airflow within 10 percent of the whole-house mechanical exhaust airflow rate. The supply air handler shall provide supply air to each habitable space in the residential unit. The whole-house ventilation system shall include exhaust fans in accordance with Section 403.4.6.2 to meet the pressure equalization requirements of Section 501.4. The flow rate for the outdoor air intake must be tested and verified at the minimum ventilation fan speed and the maximum heating or cooling fan speed. The results of the test shall be submitted and posted in accordance with Section 403.4.6.6

Whole-house mechanical ventilation systems shall be provided with advanced controls that are configured to operate the system with intermittent off operation and shall operate for a least two hours in each four-hour segment. The whole house ventilation airflow rate determined in accordance with Section 403.4.2 as corrected by Section 403.4.3 shall be multiplied by the factor determined in accordance with Table 403.4.6.5.

TABLE 403.4.6.5

INTERMITTENT WHOLE-HOUSE MECHANICAL VENTILATION RATE FACTORSa, b

RUN-TIME PERCENTAGE
EACH 4-HOUR SEGMENT
50% 66% 75% 100%
Factora 2 1.5 1.3 1.0
  1. For ventilation system run-time values between those given, the factors are permitted to be determined by interpolation.
  2. Extrapolation beyond the table is prohibited.
Whole-house mechanical ventilation systems shall be tested, balanced and verified to provide a flow rate not less than the minimum required by Sections 403.4.2 and 403.4.3. Testing shall be performed according to the ventilation equipment manufacturer's instructions, or by using a flow hood, flow grid, or other airflow measuring device at the mechanical ventilation fan's inlet terminals, outlet terminals or grilles or in the connected ventilation ducts. Where required by the building official, testing shall be conducted by an approved third party. A written report of the results of the test shall be signed by the party conducting the test and provided to the building official and shall be posted in the residential unit in accordance with Section 403.4.6.7.
A permanent certificate shall be completed by the mechanical contractor, test and balance contractor or other approved party and posted on a wall in the space where the furnace is located, a utility room, or an approved location inside the building. When located on an electrical panel, the certificate shall not cover or obstruct the visibility of the circuit directory label, service disconnect label, or other required labels. The certificate shall list the flow rate determined from the delivered airflow of the whole-house mechanical ventilation system as installed and the type of mechanical whole-house ventilation system used to comply with Section 403.4.3.

Bathrooms, toilet rooms and kitchens shall include a local exhaust system. Such local exhaust systems shall have the capacity to exhaust the minimum airflow rate in accordance with Table 403.4.7 and Table 403.3.1.1, including notes. Fans required by this section shall be provided with controls that enable manual override or automatic occupancy sensor, humidity sensor or pollutant sensor controls. An "on/off" switch shall meet this requirement for manual controls. Manual fan controls shall be provided with ready access in the room served by the fan.

TABLE 403.4.7

MINIMUM EXHAUST RATES

AREA TO BE EXHAUSTED EXHAUST RATE
INTERMITTENT CONTINUOUS
Kitchens 100 cfm 30 cfm
Bathrooms—toilet
rooms
50 cfm 20 cfm

For SI: 1 cubic foot per minute = 0.02832 m3/min.

If the local exhaust fan is included in a whole-house ventilation system in accordance with Section 403.4.6, the exhaust fan shall be controlled to operate as specified in Section 403.4.5.

Exhaust fans shall meet the following criteria.

  1. Exhaust fans shall be tested and rated in accordance with HVI 915, HVI 916, and HVI 920.

    Exception: Where a range hood or down draft exhaust fan is used for local exhaust for a kitchen, the device is not required to be rated per these standards.

  2. Fan airflow rating and duct system shall be designed and installed to deliver at least the exhaust airflow required by Table 403.4.4. The airflows required refer to the delivered airflow of the system as installed and tested using a flow hood, flow grid, or other airflow measurement device. Local exhaust systems shall be tested, balanced and verified to provide a flow rate not less than the minimum required by this section.
  3. Design and installation of the system or equipment shall be carried out in accordance with manufacturer's installation instructions.
  4. Fan airflow rating and duct system shall be designed and installed to deliver at least the exhaust airflow required by Table 403.4.3.

Exceptions:

  1. An exhaust airflow rating at a pressure of 0.25 in. w.g. may be used, provided the duct sizing meets the prescriptive requirements of Table 403.4.7.2.
  2. Where a range hood or down draft exhaust fan is used to satisfy the local ventilation requirements for kitchens, the range hood or down draft exhaust shall not be less than 100 cfm at 0.10 in. w.g.

TABLE 403.4.7.2

PRESCRIPTIVE EXHAUST DUCT SIZING

Fan Tested cfm at
0.25 inches w.g.
Minimum Flex Diameter Maximum Length
(in Feet)
Minimum Smooth
Diameter
Maximum Length
(in Feet)
Maximum Elbowsa
50 4 inches 25 4 inches 70 3
50 5 inches 90 5 inches 100 3
50 6 inches No Limit 6 inches No Limit 3
80 4 inchesb Not Allowed 4 inches 20 3
80 5 inches 15 5 inches 100 3
80 6 inches 90 6 inches No Limit 3
100 5 inchesb Not Allowed 5 inches 50 3
100 6 inches 45 6 inches No Limit 3
125 6 inches 15 6 inches No Limit 3
125 7 inches 70 7 inches No Limit 3

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.

  1. For each additional elbow, subtract 10 feet from length.
  2. Flex ducts of this diameter are not permitted with fans of this size.

Mechanical ventilation systems for enclosed parking garages shall operate continuously or shall be automatically operated by means of carbon monoxide detectors applied in conjunction with nitrogen dioxide detectors. Such detectors shall be listed in accordance with UL 2075 and installed in accordance with their listing and the manufacturers' instructions. Automatic operation shall cycle the ventilation system between the following two modes of operation:

  1. Full-on at an airflow rate of not less than 0.75 cfm per square foot [0.0038 m3/(s • m2)] of the floor area served.
  2. Standby at an airflow rate of not less than 0.05 cfm per square foot [0.00025 m3/(s • m2)] of the floor area served.
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 403.3.1.
In buildings used for the repair of automobiles, each repair stall shall be equipped with an exhaust extension duct, extending to the outside of the building. Exhaust extension ducts over 10 feet (3048 mm) in length shall mechanically exhaust at least 300 cfm (8.50 m3/min). Connecting offices and waiting rooms shall be supplied with conditioned air under positive pressure.
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.

Mechanical ventilation for health care facilities licensed by Washington State shall be designed and installed in accordance with this code and the following provisions of the Washington Administrative Code (WAC):

  1. Mechanical ventilation in ambulatory care facilities shall comply with Chapter 246-330 WAC.
  2. Mechanical ventilation for acute-care hospitals shall comply with Chapter 246-320 WAC.
  3. Mechanical ventilation for nursing homes shall comply with Chapter 388-97 WAC.

Mechanical ventilation for unlicensed ambulatory care facilities shall be designed and installed in accordance with this code and ASHRAE 170.

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