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PDFWAC 51-52-0403

Section 403Mechanical 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. The system 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.
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.
403.2.1 Recirculation of air. 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 10 percent or more 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. 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.
403.3Outdoor air and local exhaust airflow rates. 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.
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, 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 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 not be 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 ft2a
People Outdoor Airflow Rate in Breathing Zone Rp
cfm/Person
Area Outdoor Airflow Rate in Breathing Zone Ra
cfm/ft2a
Exhaust Airflow Rate cfm/ft2a
Offices
 
 
 
 
 
Conference rooms
50
5
0.06
 
Kitchenettesk
25
5
0.06
0.30
 
Office spaces
5
5
0.06
 
Reception areas
30
5
0.06
 
Telephone/data entry
60
5
0.06
 
Main entry lobbies
10
5
0.06
Private dwellings, single and multiple
 
 
 
 
 
Garages, common for multiple unitsb
0.75
 
 
 
 
 
See Table 403.4.7
 
Living areasc
 
See Table 403.4.2
 
Toilet rooms, bathrooms and laundry areasg, i
 
See Table 403.4.7
Public spaces
 
 
 
 
 
Corridors serving other than Group R occupancies
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
 
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 showerhead)g
50/20f
 
Smoking loungesb
70
60
 
Toilet rooms—Publicg
50/70e
Sports and amusement
 
 
 
 
 
Disco/dance floors
100
20
0.06
 
Bowling alleys (seating areas)
40
10
0.12
 
Game arcades
20
7.5
0.18
 
Ice arenas, without combustion enginesj
0.30
0.5
 
Gym, stadium, arena (play area)j
0.30
 
Spectator areas
150
7.5
0.06
 
Swimming pools (pool and deck area)
0.48
 
Health club/aerobics room
40
20
0.06
 
Health club/weight room
10
20
0.06
Storage
 
 
 
 
 
Janitor closets, trash rooms, recycling rooms
1.0
 
Repair garages, enclosed parking garageb, d
0.75
 
Storage rooms, chemical
1.5
 
Warehouses
0.06
Workrooms
 
 
 
 
 
Bank vaults/safe deposit
5
5
0.06
 
Darkrooms
1.0
 
Copy, printing rooms
4
5
0.06
0.5
 
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
 
Computer (without printing)
4
5
0.06
For SI:
 
1 cubic foot per minute = 0.0004719 m3/s, 1 ton = 908 kg, 1 cubic foot per minutes 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. Recirculation of air that is contained completely within such spaces shall not be 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 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 occupied.
g.
 
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 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).
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.
 
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.
j.
 
When combustion equipment is intended to be used on the playing surface, additional dilution ventilation and/or source control shall be provided.
k.
 
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.
403.3.1.1.2.3 Multiple zone recirculating systems. For ventilation systems wherein one or more air handlers supply a mixture of outdoor air and recirculated air to more than one ventilation zone, the outdoor air intake flow (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 Uncorrected outdoor air intake. The uncorrected outdoor air intake flow (Vot) shall be determined in accordance with Equation 4-5.
Vou = Dall zones(Rp × Pz) + ∑all zones(Ra × Az)(Equation 4-5)
403.3.1.1.2.3.1.1 Occupant diversity. 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.
D = Ps/∑all zonesPz(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 Vouvalue is no less than that determined using Equation 4-5.
403.3.1.1.2.3.1.2 Design system population. 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.
403.3.1.1.2.3.2 System ventilation efficiency. 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.
403.3.1.1.2.3.3 Simplified procedure.
403.3.1.1.2.3.3.1 System ventilation efficiency. System ventilation efficiency (Ev) shall be determined in accordance with Equation 4-6a or 4-6b.
Ev = 0.88 × D + 0.22 for D < 0.60 (Equation 4-6a)
Ev = 0.75 for D ≥ 0.60 (Equation 4-6b)
403.3.1.1.2.3.3.2 Zone minimum primary airflow. For each zone, the minimum primary airflow (Vpz-min) shall be determined in accordance with Equation 4-7.
Vpz-min = Voz × 1.5 (Equation 4-7)
403.3.1.1.2.3.4 Outdoor air intake. The design outdoor air intake flow (Vot) shall be determined in accordance with Equation 4-8.
Vot = Vou/Ev(Equation 4-8)
403.3.2 Group R-2, R-3 and R-4 occupancies. This section is not adopted. See Section 403.4.
403.3.2.1 Outdoor air for dwelling units. This section is not adopted.
403.3.2.2 Outdoor air for other spaces. This section is not adopted.
403.3.2.3 Local exhaust. This section is not adopted.
403.4 Group R whole house mechanical ventilation system. 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 requirement of natural ventilation requirements of Section 402 or the mechanical ventilation requirements of Sections 403.1 through 403.3.
403.4.1 System design. 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.
Table 403.4.2
WHOLE HOUSE MECHANICAL VENTILATION AIRFLOW RATE
(CONTINUOUSLY OPERATING SYSTEMS)
Floor Area
(ft2)
 
Bedrooms1
 
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
 
1 Minimum airflow (Qr) is set at not less than 30 cfm for each dwelling units.
403.4.2 Whole house mechanical ventilation rates. 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 rates 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.
Qr = 0.01*Afloor + 7.5*(Nbr + 1) (Equation 4-10)
where:
Qr
=
Ventilation airflow rate, cubic feet per minute (cfm) but not less than 30 cfm for each dwelling unit.
Afloor
=
Conditioned floor area, square feet (ft2)
Nbr
=
Number of bedrooms, not less than one.
Table 403.4.3
SYSTEM COEFFICIENT (Csystem)
System Type
Distributed
Not Distributed
Balanced
1.0
1.25
Not Balanced
1.25
1.5
403.4.3 Ventilation quality adjustment. 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.
Qv = Qr* Csystem(Equation 4-11)
where:
Qv
=
Quality-adjusted ventilation airflow rate in cubic feet per minute (cfm)
Qr
=
Ventilation airflow rate, cubic feet per minute (cfm) from Equation 4-10 or Table 403.4.1
Csystem
=
System coefficient from Table 403.4.3
403.4.4 Whole house ventilation residential occupancies. Residential dwelling and sleeping unit whole house ventilation systems shall meet the requirements of Sections 403.4.4.1 or 403.4.4.2 depending on the occupancy of the residential unit.
403.4.4.1 Whole house ventilation in Group R-2 occupancies. 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.
403.4.4.2 Whole house ventilation for other than Group R-2 occupancies. 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.
403.4.6 Whole house ventilation system component requirements. 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 transfer fan or a 25 square foot 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.
403.4.6.1 Exhaust fans. 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 and equipped with backdraft dampers or motorized dampers in accordance with 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.
403.4.6.2 Supply fans. 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 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.
403.4.6.3 Balanced whole house ventilation system. 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 403.4.2 is utilized to correct the whole house mechanical ventilation rate. The system shall be design 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.
403.4.6.4 Furnace integrated supply. 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 air flow 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. 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.
403.4.6.5 Intermittent off operation. 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 in Each 4-hour Segment
50%
66%
75%
100%
Factora
2
1.5
1.3
1.0
a
For ventilation system run-time values between those given, the factors are permitted to be determined by interpolation.
b
Extrapolation beyond the table is prohibited.
403.4.6.6 Testing. 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.
403.4.6.7 Certificate. 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.
403.4.7 Local exhaust. 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
403.4.7.1 Whole house exhaust controls. 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.
403.4.7.2 Local exhaust fans. 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 manufacturers' 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
 
NA
4 inches
 
20
3
 
80
 
5 inches
 
15
5 inches
 
100
3
 
80
 
6 inches
 
90
6 inches
 
No Limit
3
 
100
 
5 inchesb
 
NA
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
 
a.
For each additional elbow, subtract 10 feet from length.
b.
Flex ducts of this diameter are not permitted with fans of this size.
[Statutory Authority: RCW 19.27.031 and 19.27.074. WSR 20-03-041, § 51-52-0403, filed 1/8/20, effective 7/1/20; WSR 17-10-075, § 51-52-0403, filed 5/3/17, effective 6/3/17; WSR 16-01-148, § 51-52-0403, filed 12/21/15, effective 7/1/16. Statutory Authority: RCW 19.27.031, 19.27.074 and chapters 19.27 and 34.05 RCW. WSR 13-04-053, § 51-52-0403, filed 2/1/13, effective 7/1/13. Statutory Authority: RCW 19.27.031, 19.27.035, 19.27.074, and chapters 19.27 and 34.05 RCW. WSR 12-07-020, § 51-52-0403, filed 3/12/12, effective 4/12/12. Statutory Authority: RCW 19.27.190, 19.27.074, 19.27.031 and chapters 19.27 and 34.05 RCW. WSR 10-03-099, § 51-52-0403, filed 1/20/10, effective 7/1/10. Statutory Authority: RCW 19.27.190, 19.27.020, and chapters 19.27 and 34.05 RCW. WSR 07-01-092, § 51-52-0403, filed 12/19/06, effective 7/1/07. Statutory Authority: RCW 19.27.020, 19.27.031, 19.27.074 and chapters 19.27 and 34.05 RCW. WSR 05-01-015, § 51-52-0403, filed 12/2/04, effective 7/1/05.]
Reviser's note: The brackets and enclosed material in the text of the above section occurred in the copy filed by the agency.
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