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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.
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.
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 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.
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.
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.
SYSTEM COEFFICIENT (Csystem)
SYSTEM TYPE DISTRIBUTED NOT DISTRIBUTED
Balanced 1.0 1.25
Not Balanced 1.25 1.5
403.4.4 Whole-House Ventilation Residential Occupancies
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.
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.
403.4.5 Whole-House Ventilation System Controls
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.
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 (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.
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 (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.
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 (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
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 403.4.3 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.
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 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
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.
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.
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.
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