Indoor Ventilation

Washington State Indoor Ventilation Code Requirements

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M1505.4.2 System controls. The whole-house mechanical ventilation system shall be provided with
controls that 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 with ready access by the occupant.
2. 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 be readily accessible by the occupant.
3. Whole house ventilation systems shall be configured to operate continuously except where intermittent off controls and sizing are provided per Section M1505.4.3.2.

M1505.4.3.1 Ventilation quality adjustment. The minimum whole house ventilation rate from Section
1505.4.3 shall be adjusted by the system coefficient in Table M1505.4.3(2) 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.

M1505.4.3.2 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 shall operate for a least two hours in each four-hour segment. The whole house ventilation
airflow rate determined in accordance with Section M1505.4.3 as corrected by Section M1505.4.3.1 is
multiplied by the factor determined in accordance with Table M1505.4.3(3).

M1505.4.4 Local exhaust rates. Local exhaust systems shall be designed to have the capacity to
exhaust the minimum airflow rate determined in accordance with Table M1505.4.4(1). If the local exhaust
fan is included in the whole house ventilation system, in accordance with Section 1505.4.1, then the
exhaust fan shall be controlled to operate as specified in Section M1505.4.2.

M1505.4.4.1 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 M1505.4.4(1). 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 readily
accessible in the room served by the fan.

M1505.4.4.2 Local exhaust fans. Exhaust fans shall meet the following criteria:

1. Exhaust fans shall be tested and rated in accordance with the airflow and sound rating
   procedures of the Home Ventilating Institute (HVI 915, HVI Loudness Testing and Rating
   Procedure, HVI 916, HVI Airflow Test Procedure, and HVI 920, HVI Product Performance
   Certification Procedure).  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 M1505.4.4(1). 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 M1505.4.4(1).

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 M1505.4.4(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.

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