4.6 Indoor Air Quality and Mechanical Ventilation

As residential buildings have been tightened over the last several code cycles to improve energy performance, the dilution of indoor air through natural ventilation has been significantly reduced. As a result, the importance of controlling indoor pollutants generated by kitchen ranges during food preparation and from common building materials, cleaners, finishes, packaging, furniture, carpets, clothing, and other products has increased. Energy Commission-sponsored research has revealed that concentration of pollutants such as formaldehyde are higher than expected, and that many occupants do not open windows regularly for ventilation. The 2019 Energy Standards include requirements for mandatory mechanical ventilation intended to improve indoor air quality (IAQ) in homes, and requirements for MERV 13 air filtration on space conditioning systems, and ventilation systems that provide outside air to the occupiable space of a dwelling.

As specified by §150.0(o), single-family detached dwelling units, and multifamily attached dwelling units must meet the requirements of ASHRAE Standard 62.2-2016 including Addenda b, d, l, q, and s (ASHRAE 62.2), subject to the amendments specified in Section 150.0(o)1. A copy of this version of ASHRAE 62.2 may be obtained at the following URL:

[insert link to ASHRAE bookstore for this version of ASHRAE 62.2 when it becomes available]

Opening and closing windows and continuous operation of central fan-integrated ventilation systems are not allowable options for meeting dwelling unit ventilation requirements. The requirements of ASHRAE Standard 62.2 focus on providing continuous dwelling unit mechanical ventilation, as well as local exhaust ventilation at known sources of pollutants or moisture, such as kitchens, bathrooms, and laundries.

Limiting the sources of indoor pollutants is one important method for protecting indoor air quality. Kitchen ranges used for preparation of food have been identified as a source of indoor air pollution that must be addressed, and builders should adhere to the requirements of Section 4.504 of the California Green Building Standards Code for the selection of materials and finishes that have no or low emissions of air pollutants such as formaldehyde and volatile organic compounds (VOCs). The California Air Resources Board (CARB) also provides guidance for reducing indoor air pollution in homes. For more information, see the CARB Indoor Air Quality Guidelines:

http://www.arb.ca.gov/research/indoor/guidelines.htm

This section will cover compliance and enforcement, typical design solutions, energy consumption issues, and other requirements specified by ASHRAE 62.2 as amended in the 2019 Title 24 standards. The key changes in the adopted 2016 version of ASHRAE 62.2 and Title 24 Part 6 amendments to 62.2 include the following:

1.   ASHRAE 62.2 now covers mid-rise and high-rise residential occupancies, as well as single-family detached and low-rise attached multifamily dwellings.

2.   For single-family homes, the standard requires higher rates of dwelling unit mechanical ventilation than previously. An adjustment to the ventilation rate is provided to account for the effects of the envelope infiltration, which varies by climate zone (Table 4-14). Homes sealed to a leakage rate of less than 2 ACH50 will require larger fans to compensate for the decrease in effective ventilation due to infiltration.

3.   Single-family detached dwellings and townhomes using balanced ventilation systems will require lower ventilation rates as compared to the rates required when exhaust or supply-only ventilation is used.

4.   Compliance with required dwelling unit ventilation using variable mechanical ventilation systems (intermittent or variable operation) requires the average mechanical ventilation rate (in CFM) over a three-hour period to be greater than or equal to the ventilation rate used for continuous ventilation. Otherwise, more complicated control strategies may be used if the system operation complies with the “relative exposure” calculations in normative Appendix C of ASHRAE 62.2.

5.   Two options for compliance with dwelling unit ventilation are allowed for multifamily attached dwelling units: (1) installation of a balanced ventilation system or (2) installation of an exhaust or supply-only system accompanied by sealing to a leakage rate of not more than 0.3 CFM50 per ft² of dwelling unit enclosure surface area.

6.   Kitchen range hood fans are now required to be verified by a HERS Rater. The new verification protocol requires comparing the installed model to ratings in the Home Ventilating Institute (HVI) directory of certified ventilation products to confirm the installed range hood is rated to meet the required airflow and sound requirements specified in ASHRAE 62.2. See section 4.6.7 below for more detail. Kitchen range hood fans that exhaust more than 400 CFM at minimum speed are exempt from this requirement.

Compliance with the dwelling unit ventilation airflow specified in ASHRAE 62.2 is required in new dwelling units, in new dwelling units that are additions to an existing building, and in additions to existing dwelling units that increase the conditioned floor area of the existing dwelling unit by more than 1,000 square feet. Alterations to components of existing buildings that previously met any requirements of ASHRAE 62.2 must continue to meet requirements upon completion of the alteration(s).

The following summarizes the key requirements for most newly constructed buildings:

1.  A dwelling unit mechanical ventilation system shall be provided. Typical solutions are described in Section 4.6.2 below. The airflow rate provided by the system shall be confirmed through field verification and diagnostic testing in accordance with the applicable procedures specified in Reference Residential Appendix RA3.7.

2.  Kitchens and bathrooms shall have local exhaust fans vented to outdoors.

3.  Clothes dryers shall be vented to outdoors.

Miscellaneous indoor air quality design requirements also apply, including the following:

1.  Ventilation air shall come from outdoors and shall not be transferred from adjacent dwelling units, garages, unconditioned attics or crawl spaces.

2.  Ventilation system controls shall be labeled, and the homeowner shall be provided with instructions on how to operate the system.

3.  Combustion appliances shall be properly vented, and exhaust systems shall be designed to prevent back drafting.

4.  Walls and openings between the house and the garage shall be sealed or gasketed.

5.  Habitable rooms shall have windows with an opening ventilation area of at least 4 percent of the floor area.

6.  Mechanical systems including heating and air-conditioning systems that supply air to habitable spaces shall have MERV 13 filters or better and be designed to accommodate the rated pressure drop of the system air filter at the designed airflow rate.

7.  Dedicated air inlets (not exhaust) that are part of the ventilation system design shall be located away from known sources of outdoor contaminants.

8.  A carbon monoxide alarm shall be installed in each dwelling unit in accordance with NFPA Standard 720.

9.  Air-moving equipment used to meet the dwelling unit ventilation requirement and the local ventilation exhaust requirement shall be rated in terms of airflow and sound:

a.  Dwelling unit ventilation and continuously operating local exhaust fans must be rated at a maximum of 1.0 sone (measurement of sound).

b.  Demand-controlled local exhaust fans must be rated at a maximum of 3.0 sone.

c.  Kitchen exhaust fans must be rated at a maximum of 3.0 sone at one or more airflow settings greater than or equal to 100 CFM.

d.  Remotely located air-moving equipment (mounted outside habitable spaces) are exempt from the sound requirements provided there is at least 4 feet of ductwork between the fan and the interior grille.

4.6.1    Compliance and Enforcement

Compliance with ASHRAE 62.2 requirements must be verified by the enforcement agency, except for the following requirements that must be HERS verified in accordance with the procedures in Residential Appendix RA3.7:

•      Dwelling unit ventilation airflow rate

•      HVI ratings for kitchen range hood fans

All applicable certificates of compliance, installation, and verification must be registered with an approved HERS Provider.

Title 24 Part 6 amendments to ASHRAE 62.2 eliminated the requirement to use the result of a blower door measurement when calculating the required dwelling unit mechanical ventilation rate (Q_fan). Instead, the Qf_an calculation applies a default infiltration leakage rate equivalent to 2 ACH₅₀. Blower door testing to measure actual dwelling unit enclosure leakage is required only when performance compliance modeling uses an infiltration leakage rate less than 2 ACH₅₀ - which requires HERS verification of dwelling unit enclosure leakage for energy compliance as well as for determining Q_fan.

If a central heating/cooling system air-handler fan is used to ventilate the dwelling (central fan-integrated ventilation, also known as CFI ventilation), the air-handler must meet or exceed the mandatory fan efficacy criteria. This requires the installer to perform the test given in Reference Appendix RA3.3 and a HERS Rater to verify the efficacy (W/CFM) of the air-handling unit fan.

4.6.1.1    Certificate of Compliance Reporting Requirements

When using the prescriptive compliance approach, the mechanical ventilation rate (Q_fan) must be manually calculated using the applicable equations in Standards Section 150.0(o)1, also shown in Section 4.6.4 below. The value for Q_fan is required to be reported on the CF1R. When using the performance method, the compliance model automatically calculates Q_fan based on the inputs for conditioned floor area, number of bedrooms, and climate zone (Table 4-14), and uses the Q_fan ventilation airflow value when calculating the building energy use. The performance certificate of compliance (CF1R) will report the:

1.  Minimum mechanical ventilation airflow rate (calculated value) that must be delivered by the system.

2.  Type of ventilation system (exhaust, supply, balanced, CFI).

3.  Fan efficacy (W/CFM) for the selected system.

4.  Recovery efficiency (%) (applicable to HRV/ERV system types only)

5.  For CFI systems--HERS verification of air handler fan efficacy is required.

The installed dwelling unit ventilation system must conform to the performance requirements on the CF1R.

The enforcement agency may require additional information/documentation describing the ventilation systems be submitted along with the CF1R at plan check.

4.6.1.2    Certificate of Installation and Certificate of Verification Reporting Requirements

The builder/installer must complete certificates of installation (CF2R-MCH-01 and CF2R-MCH-27) for the dwelling. The HERS Rater must complete a certificate of verification (CF3R-MCH-27) for the dwelling.

4.6.1.2.1    CF2R-MCH-01

The following information must be provided on the CF2R-MCH-01 to identify each ventilation system/fan in the dwelling that will require HERS verification.

For dwelling unit ventilation systems:

1.   Ventilation system name or identification

2.   Ventilation system location

3.   Ventilation system control type (i.e. continuous, variable)

4.   Ventilation system type (i.e. exhaust, supply, balanced, CFI).

5.   Ventilation system target airflow rate (may be less than Q_fan if using multiple systems/fans to comply)

6.   Ventilation system manufacturer name

7.   Ventilation system model number

8.   Control system manufacturer (if applicable)

9.   Control system model number (if applicable)

10.  Energy Commission certification number for variable system/control (if applicable)

For kitchen exhaust ventilation systems:

1.   Kitchen exhaust control type (i.e. demand-controlled, continuous)

2.   Kitchen exhaust system type (i.e. range hood, over the range (OTR) microwave, downdraft, local exhaust, other).

3.   Kitchen exhaust system required airflow rate

4.   Kitchen exhaust system manufacturer name

5.   Kitchen exhaust system model number

6.   Kitchen exhaust system HVI certification number

4.6.1.2.2    CF2R-MCH-27

The following additional information must be provided on the CF2R-MCH-27 to document compliance with §150.0(o). Refer also to the procedures in RA 3.7.4.

For dwelling unit ventilation systems:

•      Measured airflow rate of the installed dwelling unit ventilation system. For balanced systems, exhaust and supply airflows must be measured and recorded.

For kitchen exhaust ventilation systems:

•      Confirmation the installed system is rated by HVI to meet the required airflow and sound requirements.

For all ventilation systems:

•      Confirmation that the other applicable requirements given in Sections 6 and 7 of ASHRAE 62.2 as amended in §150.0(o)1 have been met (see Sections 4.6.7 and 4.6.8 below).

4.6.1.2.3    CF3R-MCH-27

The following additional information must be provided on the CF3R-MCH-27 to document compliance with §150.0(o):

For dwelling unit ventilation systems:

•      Measured airflow rate of the installed dwelling unit ventilation system. For balanced systems, both exhaust and supply airflows must be measured and recorded.

For kitchen exhaust ventilation systems:

•      Confirmation the installed system is rated by HVI to meet the required airflow and sound requirements.

4.6.2    Typical Solutions for Single-Family Dwelling Unit Ventilation

There are four typical solutions for meeting the dwelling unit outside air ventilation requirement:

1.  Exhaust ventilation - air is exhausted from the dwelling unit and replaced by infiltration.

2.  Supply ventilation - outdoor air is supplied directly to the dwelling unit after being filtered.

3.  Central fan-integrated ventilation - outdoor air is ducted to the return plenum of the central space conditioner air handler. Both return air and outdoor air must be filtered.

4.  Balanced ventilation – may be a single packaged unit containing supply and exhaust fans that move approximately the same airflow through a heat or energy recovery core, or may use separate fans without heat exchange. In both cases, air supplied from outdoors must be filtered. (See Section 4.4.1.14 for filter requirements.)

4.6.2.1    Exhaust Ventilation

Exhaust ventilation is typically provided using a quiet, continuously operating ceiling-mounted fan or attic-mounted inline fan. Air is drawn from the house or unit and exhausted to the outdoors. Outdoor air enters the house or unit through infiltration. Many high-quality, quiet fans are available for this purpose. For larger homes, more than one fan may be used. The same fan can be used to meet dwelling unit and local (bathroom or laundry) exhaust ventilation requirements. Inline fans can be used to exhaust air from one or more bathrooms. Remotely located fans (fans mounted outside habitable spaces) are exempt from the sound requirements if there is at least 4 feet of ductwork between the fan and the interior grille.

Figure 4-28: Exhaust Ventilation Example

Source: California Energy Commission

4.6.2.2    Supply Ventilation

Supply ventilation systems draw outdoor air into the house using a dedicated supply fan and most likely distribute ventilation air through supply ductwork, although that is not a requirement. Indoor air escapes through leaks in the building envelope (exfiltration), as shown in Figure 4-29. For larger homes, more than one fan may be used. Remotely located fans (fans mounted outside habitable spaces) are exempt from the sound requirements if there is at least 4 feet of ductwork between the fan and the interior grille. Thus, if less than 4 feet of ductwork are used, the supply fan must meet the maximum 1.0 sone rating requirement for dwelling unit ventilation fans.

Figure 4-29: Supply Ventilation Example

Source: California Energy Commission

Section 150.0(m)12 requires that outside air be filtered using MERV 13 (or greater) particle removal efficiency rated air filters. The filters must be accessible to facilitate replacement. Supply systems may locate the MERV 13 air filter either upstream or downstream of the fan as long as the incoming outdoor air is filtered prior to delivery to the dwelling unit habitable space. Fans may be located in attics, dropped ceiling spaces, or other spaces dedicated for installation of mechanical equipment.

The outdoor air inlet should be located to avoid areas with contaminants such as smoke produced in barbeque areas and products of combustion emitted from gas appliance vents. Air may not be drawn from attics or crawlspaces. To minimize drafts and optimize distribution, supply air can be ducted directly to bedrooms and living areas using an appropriately sized and sealed ventilation-only duct system or by connecting to the HVAC supply plenum.

4.6.2.3    Central Fan-Integrated (CFI) Ventilation

The central forced-air system air handler can be configured to function as a ventilation supply system by installing an outdoor air duct that connects the return plenum of the air-handler to outdoors. This strategy, called CFI ventilation, uses negative pressure in the return plenum to draw in outdoor air, which is mixed and distributed with a larger volume of return air from the house.  A motorized damper and special CFI controls must be installed to ensure the air handler delivers the required ventilation airflow regardless of whether the heating/cooling system operates to provide space conditioning. Thus, when the heating/cooling operating time is reduced during times when space conditioning is not needed, the CFI controls will operate only the system fan and outdoor air damper to provide ventilation air even if space conditioning is not needed. Because of the relatively high energy use of the central system fan, CFI systems consume greater amounts of energy compared to exhaust or supply or balanced ventilation systems. Continuous operation of the CFI air handler fan to provide the required dwelling unit ventilation is prohibited.

Figure 4 30: Central Fan-Integrated (CFI) Ventilation Example

Source: California Energy Commission

Section 150.0(m)12 requires that outside air be filtered using MERV 13 (or greater) particle removal efficiency rated air filters. Filters must be accessible to simplify replacement. For CFI systems, the filters must be installed upstream of the cooling or heating coil; thus, the filter rack provided at the inlet to the air handler may be used. Otherwise, filters must be provided at the return grill(s) for the central fan, and another filter must be provided in the outside air ductwork before the point the outside air enters the return plenum of the central fan.

When considering system design and HERS verification compliance for CFI ventilation systems, it is important to distinguish between the central forced-air system fan total airflow and the much smaller outdoor ventilation airflow rate (the airflow that is induced to flow into the return plenum from outdoors). Both of these airflows must be verified by a HERS Rater. Refer to Figure 4-30 and note that the total airflow through the air handler is the sum of the return airflow and the ventilation airflow.

CFI ventilation systems, devices, and controls may be approved for use for compliance with the HERS field verification requirements for dwelling unit mechanical ventilation airflow. CFI ventilation systems must be automatically controlled by a timer or other device that assures they will operate the minimum amount of time needed to meet the ventilation requirement. The scheduling of the automatic controls must be such that the fan operates at least once every three hours and the average dwelling unit ventilation rate over any 3-hour period must be greater than or equal to the required ventilation rate Q_fan calculated using the applicable equations in Standards §150.0(o)1 (also shown in Section 4.6.4 below).

Section §150.0(o)1B specifically prohibits continuous operation of the central forced-air system of a CFI ventilation system, so CFI ventilation systems must operate intermittently and be certified to the Energy Commission as an intermittent or variable system that will meet the minimum ventilation airflow required by §150.0(o).

A listing of certified CFI ventilation systems is posted at the following URL:

http://www.energy.ca.gov/title24/equipment_cert/imv/

The outside air ducts for CFI ventilation systems are not allowed to be sealed/taped off during duct leakage testing. However, CFI outdoor air ductwork that uses controlled motorized dampers that open only when outdoor air ventilation is required and close when outdoor air ventilation is not required may be closed during duct leakage testing.

Because CFI ventilation systems can use a large amount of electricity annually compared to other ventilation system types, the air handlers used in CFI ventilation systems are required to meet the fan watt draw requirements given in Section 150.0(m)13B in all climate zones.

4.6.2.4    Balanced Ventilation

Balanced systems use an exhaust fan and a supply fan to move approximately the same volume of air into and out of the dwelling. To be considered a balanced ventilation system, the total supply airflow and the total exhaust airflow must be within 20 percent of each other. For determining compliance, the average of the supply and exhaust airflows is equal to the balanced system airflow rate. (Refer to RA3.7.4.1.2.)

Some balanced systems are small packaged systems that include heat exchangers that temper incoming air with outgoing air, which reduces the thermal effect of ventilation on heating and cooling loads, but the dual fans also increase electrical energy use. They are most practical for use in tightly sealed houses and in multifamily units where exhaust type systems have difficulty drawing adequate outside air due to limited exterior wall area.

Like supply ventilation systems, balanced systems are required to be equipped with MERV 13 or better filters to remove particles from outside airflow. An example of a heat recovery ventilator is shown in Figure 4-31.

The outdoor air inlet should be located to avoid areas with contaminants such as smoke produced in barbeque areas and products of combustion emitted from gas appliance vents. Air may not be drawn from attics or crawlspaces.

Figure 4-31: Balanced Ventilation Example 1 – HRV or ERV

Source: California Energy Commission

Another balanced system configuration uses a stand-alone supply fan coupled with a stand-alone exhaust fan, both wired to a common switch or control to ensure they operate simultaneously. The controls must make it possible to adjust the speed of the fans for balancing the airflows. An example is shown in Figure 4-32.

Figure 4-32: Balanced Ventilation Example 2 – Separate Supply and Exhaust Fan

Source: California Energy Commission

4.6.3    Typical Solutions for Multifamily Dwelling Unit Ventilation

4.6.3.1    System Types

There are generally three system types available for meeting the dwelling unit ventilation requirement (refer to Section 4.6.2 for descriptions of the system types described below):

1.   Exhaust ventilation – air is exhausted from the dwelling unit and replaced by infiltration.

2.   Supply ventilation – outdoor air is supplied directly to the dwelling unit after being filtered.

3.   Balanced ventilation – may be a single packaged unit containing supply and exhaust fans that moves approximately the same airflow through a heat or energy recovery core or may use separate fans without heat exchange. In both cases, air supplied from outdoors must be filtered. (See Section 4.4.1.14 for air filter requirements.)

Exhaust and balanced systems are most frequently used in multifamily buildings, but supply ventilation may also be used. Exhaust (or supply) systems in low-rise buildings typically use fans located in the dwelling units that exhaust directly to the outdoors.

4.6.3.2    Multifamily Building Central Shaft Ventilation Systems

Use of central ventilation fans/shafts that are shared with multiple dwelling units in the building are more common in mid-rise and high-rise buildings. When a supply or exhaust system provides dwelling unit ventilation to more than one dwelling unit, the airflows in each dwelling unit must be equal to or greater than the required (minimum) ventilation rate, and the airflows for each dwelling unit must also be balanced to be no more than 20 percent greater than the specified rate (See Standards §150.0(o)1F). The specified rate for the systems that share a common fan/shaft may be the minimum rate required for compliance, in which case each of the dwellings receiving airflow from a common fan/shaft must have ventilation airflow no more than 20 percent greater than the minimum dwelling unit ventilation airflow required by Equation 150.0-B. If the lowest airflow provided to any of the dwellings served by the common fan/shaft is a specific percent value greater than the minimum required for compliance, then the each of the dwellings receiving airflow from that common fan/shaft must have ventilation airflow no more than 20 percent greater than that lowest dwelling unit ventilation airflow.  For example, if the lowest ventilation airflow among all dwellings served by the common fan/shaft is 2 percent greater than the minimum required for compliance, then all dwellings served by the common fan/shaft must be balanced to have ventilation airflow that is no more than 22 percent greater than the minimum ventilation airflow required for compliance.

These systems must use balancing devices to ensure the dwelling-unit airflows can be adjusted to meet this balancing requirement. These system balancing devices may include, but are not limited to, constant air-regulation devices, orifice plates, and variable-speed central fans.

Since supply and exhaust ventilation system types are required to operate continuously in multifamily dwellings (see §150.0(o)1Eii), and since CFI systems are prohibited from operating continuously to provide the required dwelling unit ventilation (see §150.0(o)1B), the CFI ventilation system type is not allowed to be used in multifamily dwellings.

4.6.3.3    Multifamily Dwelling Unit Compartmentalization – Reducing Dwelling Unit Enclosure Leakage

Transfer air is the airflow between adjacent dwelling units in a multifamily building that can be a major contributor to poor indoor air quality in the dwelling units. Transfer airflow is caused by differences in pressure between adjacent dwelling units that force air to flow through leaks in the dwelling unit enclosure. The pressure differences may be due to stack effects and wind effects, but unbalanced mechanical ventilation is also a major contributor to this problem. It is desirable to minimize or eliminate leaks in all the dwelling enclosures in the building – to compartmentalize the dwellings - to prevent pollutants such as tobacco smoke, pollution generated from food preparation in the kitchen, odors, and other pollutants from being transferred to adjacent dwellings in the building.

Title 24 provides two compliance paths for mechanical ventilation which improve compartmentalization in multifamily buildings (choose one):

1.   Install a balanced ventilation system. This may consist of either a single ventilation unit (such as an ERV or HRV) or may consist of separate supply and exhaust fans that operate simultaneously and are controlled to balance the supply and exhaust airflows. The outdoor ventilation supply air must be filtered (MERV 13 or better).

2.   Verify that the dwelling unit leakage is not greater than 0.3 CFM per ft² of dwelling unit enclosure area using the procedures in RA3.8 (blower door test). If the dwelling unit enclosure passes this blower door test, use of continuously operating supply ventilation systems, or continuously operating exhaust ventilation systems in that dwelling is allowed.

4.6.4    Dwelling Unit Ventilation Airflow Measurement

Residential Appendix RA 3.7.4 provides direction for measurement of supply, exhaust, and balanced system types. These measurement procedures are applicable when there is a fixed airflow rate required for compliance, such as for systems that operate continuously at a specific airflow rate or systems that operate intermittently at a fixed speed (averaged over any three-hour period), according to a fixed timer pattern for which the programmed pattern is verifiable by a HERS Rater on site. (Refer to ASHRAE 62.2 Section 4.5.1 Short Term Average Ventilation.)

Variable or intermittent operation that complies with ASHRAE 62.2 Sections 4.5.2 and 4.5.3 complies with the dwelling unit mechanical ventilation requirements by use of varying ventilation airflow rates based on complicated calculations for relative exposure as specified in ASHRAE 62.2 Normative Appendix C. These calculation procedures provide the basis for "smart" ventilation controls implemented by use of digital controls that rely on the manufacturer's product-specific algorithms or software. Any ventilation system models that use these complex ventilation system controls in a ventilation product designed to be used to comply with Standards §150.0(o) must submit an application to the Energy Commission to have the ventilation technology approved. These manufacturers are expected to provide with their applications evidence that the system will perform to provide the required dwelling unit mechanical ventilation. The manufacturers are also expected to provide a method that could be used by a HERS Rater to verify that an installed system is operating as designed.

Listings of systems approved by the Energy Commission and certified by the manufacturer are located at the following URL:

http://www.energy.ca.gov/title24/equipment_cert/imv/

4.6.5    Dwelling Unit Ventilation Rate (Section 4 of ASHRAE 62.2)

Dwelling unit ventilation systems may operate continuously or on a short-term basis. If fan operation is not continuous, the average ventilation rate over any three-hour period must be greater than or equal to the Q_fan value calculated using the equations in this section.

ASHRAE 62.2 provides for scheduled ventilation and real-time control, but these control approaches require “equivalent exposure” calculations using methods in Normative Appendix C, and complex controls would be required to operate the fan.

Equations for calculating Q_fan (the required mechanical ventilation rate) for both single- and multifamily buildings are listed below. Single-family detached dwelling units and attached dwelling units not sharing ceilings or floors with other dwelling units, occupiable spaces, public garages, or commercial spaces (e.g. duplexes and townhomes) are allowed to take credit for the building infiltration in the calculations as described below. Use of a building infiltration credit is not applicable to calculation of the required dwelling unit mechanical ventilation for multifamily dwelling units.

A new aspect of the ventilation calculations for the 2019 standards is that the building infiltration rate (Q_inf) varies by climate zone (Table 4-14) and building height. Therefore, the value for Q_fan for a single-family dwelling or townhome will also vary based on climate zone and building height.

When the performance compliance approach is used, the compliance software completes all the calculations given in Equations 4-1, 4-2, 4-3, and 4-4, and Q_fan is reported on the CF1R. If the prescriptive compliance approach is used, the Data Registry will perform the calculations, and the value for Q_fan will be recorded on the CF1R.

4.6.5.1    Total Ventilation Rate (Qtot)

The total ventilation rate is the combined volume of ventilation air provided by infiltration and the mechanical ventilation provided from fans, as follows: 

Equation 4-1

Where:

Q_tot = total required ventilation rate (CFM)

A_floor = conditioned floor area (ft²)

N_br = number of bedrooms (not less than one)

For multifamily units, the installed ventilation system must deliver the total ventilation rate Q_tot calculated from Equation 4-1.

4.6.5.2    Infiltration Rate (Qinf)

For single-family homes, when determining the required dwelling unit mechanical ventilation airflow rate (Q_fan in Equation 4-4), the calculated value for estimated infiltration rate (Q_inf in Equation 4-2) is deducted from the value of Q_tot (determined by Equation 4-1). The calculated value for estimated infiltration rate depends on the building leakage, building height, and the weather and shielding factor, which varies by climate zone (Table 4-14). A default envelope leakage value of 2 ACH₅₀ is mandatory for the fan sizing calculations unless a blower door measurement is performed that determines a leakage rate below 2 ACH₅₀. Leakage in ACH₅₀ must be converted to CFM₅₀ for use in subsequent calculations. Conversion of 2 ACH₅₀ is shown in Equation 4-2.

Equation 4-2

Q₅₀ = V_du x 2 ACH₅₀)/ 60

Where:

Q₅₀ = leakage rate at 50 Pa, CFM

V_du = dwelling unit conditioned volume, ft³

ACH₅₀ = air changes per hour at 50 Pa (0.2 inch water)

V_du can be approximated by multiplying the average ceiling height by the dwelling conditioned floor area. If the field-verified value for ACH₅₀ is less than 2, then the verified value is used in Equation 4-2 instead of 2.

The effective annual infiltration rate (Q_inf), is calculated using the weather/shielding factor (wsf) for the applicable climate zone and the building height. See Table 4-14 below and Standards Table 150.0-D for values for wsf.

Equation 4-3

Q_inf = 0.052 x Q₅₀ x wsf x [H/H_r]²  (CFM)

Where:

Q_inf = effective annual infiltration rate, CFM

Q₅₀ = leakage rate at 50 Pa, CFM

wsf = weather and shielding factor from Table 4-14

H = vertical distance between the lowest and highest above-grade points within the pressure boundary

H_r = reference height = 8.2 ft

The number of stories multiplied by the average ceiling height (as entered in compliance software) provides sufficient accuracy for determining H.

Table 4-14: Weather and Shielding Factors by Climate Zone

4.6.5.3    Required Mechanical Ventilation Rate (Qfan)

The required mechanical ventilation rate, Q_fan is the total outside airflow required to be supplied to (or total indoor air required to be exhausted from) the building by fans. Balanced ventilation system types must provide an average of the supply and exhaust airflows that is greater than or equal to Q_fan.

Q_fan is calculated using Equation 4-4 below, which uses the values for Q_tot and Q_inf determined above. Equation 4-4 accounts for reduced exterior wall leakage area in attached units (e.g. townhomes and duplexes). Equation 4-4 also accounts for the differences in ventilation effectiveness of balanced systems compared to exhaust/supply (unbalanced) systems due to varying dwelling infiltration leakage rates. If Q_fan is less than 10 CFM, then no fan is required.

Equation 4-4

Q_fan = Q_tot - Φ ( Q_inf x A_ext)

Where:

Q_total = total required ventilation rate (CFM)

Q_inf = effective annual average infiltration rate (CFM)

Φ = 1 for balanced ventilation systems or Q_inf/Q_tot for other system types

A_ext = 1 for single-family detached homes. For attached dwelling units not sharing ceilings or floors with other dwelling units, occupiable spaces, public garages, or commercial spaces (e.g. duplexes and townhomes), A_ext is the ratio of exterior envelope surface area that is not attached to garages or other dwelling units to total envelope surface area.

For multifamily dwelling units, Q_fan = Q_tot.

4.6.5.4    Control and Operation

ASHRAE 62.2 requires that the ventilation system have an override control that is accessible to the occupants. The control must be capable of being accessed quickly and easily by the occupants. It can be a labeled wall switch or a circuit breaker located in the electrical panel, or it may be integrated into a labeled wall-mounted control. It cannot be buried in the insulation in the attic or inside the installed ventilation fan cabinet. The occupant must have easy access to modify the fan control settings or turn off the system, if necessary.

For multifamily dwelling units, the manual ON-OFF control is not required to be readily accessible to the dwelling unit occupant(s). Instead, the ventilation control may be located such that it is readily accessible to the person in charge of the multifamily building maintenance. This control strategy may be appropriate for multifamily buildings that use unbalanced (supply-only or exhaust-only) system types for which the Energy Standards require that all the ventilation systems in the building operate continuously. Continuous operation of all ventilation fans in the building tends to minimize ventilation fan-induced pressure differences between adjoining dwellings, thus reducing the leakage of transfer air between dwelling units. Transfer airflows that originate in one dwelling unit may adversely affect the indoor air quality of the other dwelling units in the building if the transfer air contains pollutants such as tobacco smoke and PM2.5 from kitchen range cooking.

Dwelling unit ventilation systems may operate continuously, or if fan operation is not continuous, the average ventilation rate over any three-hour period must be greater than or equal to the minimum dwelling unit ventilation rate calculated as described in Section 4.6.5 above.

Bathroom exhaust fans may serve a dual purpose to provide whole-dwelling unit ventilation operating at a low constant airflow rate and to provide local demand controlled ventilation at a higher "boost" airflow rate, when needed. For these system types, the continuous whole-dwelling unit airflow operation must have an ON/OFF override, which may be located in the bathroom or in a remote accessible location. The "boost" function is controlled by a separate wall switch located in the bathroom or by a motion sensor or humidistat located in the bathroom.

Time-of-day timers or duty-cycle timers can be used to control intermittent dwelling unit ventilation. Manual crank timers cannot be used, since the system must operate automatically without intervention by the occupant. Some controls “look back” over a set time interval to see if the CFI system air handler has already operated for heating or cooling before it turns on the air handler for ventilation-only operation.

See Section 4.6.4 for additional information about Energy Commission approval of ventilation controls.

4.6.6    Dwelling Unit Mechanical Ventilation Energy Consumption

For builders using the performance compliance approach, the energy use of fans (other than CFI fans) installed to meet the dwelling unit ventilation requirement is usually not an issue. The reason is the standard design W/CFM is set equal to the proposed design W/CFM up to an energy use level sufficient to accommodate most well-designed ventilation systems. Also, the standard design dwelling unit ventilation system airflow rate is set equal to the proposed design dwelling unit ventilation system airflow rate, so there is no energy penalty or credit for most systems. For balanced heat recovery or energy recovery ventilators (HRVs/ERVs), the HVI-rated recovery efficiency can be input to the performance compliance software to account for the heat recovery benefit, which helps offset higher fan energy use.

The fan efficacy of the central air handler used for a CFI ventilation system must conform to the same fan watt draw (W/CFM) limit as for cooling systems in all climate zones as verified by a HERS Rater in accordance with the diagnostic test protocols given in RA3.3. The RA3.3 verification of CFI systems determines the W/CFM of the total central system airflow, not the W/CFM of the ventilation airflow.

The Energy Standards do not regulate the energy use of ventilation fans installed for other purposes, such as local exhaust.

4.6.6.1    Central Fan-Integrated Ventilation Systems − Watt Draw

CFI system automatic controls must operate the central system air handler fan (generally part of every hour of the year) to draw in and distribute ventilation air throughout the dwelling, even when there is no heating or cooling required. The Energy Standards prohibit CFI systems from operating continuously. Because the CFI ventilation control increases the central system air handler fan run time significantly, and because typical central system air handler fan and duct systems require a large amount of power, a CFI ventilation system can use a large amount of electricity annually.

The fan efficacy of CFI systems must be verified using the same methods as required for furnaces and air handlers. (See Reference Residential Appendix RA3.3.) The central system air handler must be operating in ventilation mode with the outdoor air damper open and with ventilation air flowing into the return plenum from outside the building. Furthermore, the airflow that must be measured is the total airflow through the air handler (system airflow), which is the sum of the return airflow, and the outside air ducted to the return plenum (ventilation airflow). To pass the test, the watt draw must be less than or equal to 0.45 W/CFM for furnaces, and 0.58 W/CFM for air handlers that are not gas furnaces, or 0.62 W/CFM for small ductm high velocity systems.

4.6.6.2    Other Dwelling Unit Ventilation Systems – Watt Draw

There are no prescriptive or mandatory requirements for maximum fan energy (watt draw) for dwelling unit ventilation systems other than CFI systems.

When using the performance approach, you have the option of accepting the default minimum dwelling unit ventilation airflow rate and a watt draw value of 0.25 W/CFM, which is typical of continuous exhaust fans that meet the 1 sone requirement. Otherwise, if the installed fan has a different airflow and fan efficacy, the actual airflow rate and fan watt draw of the fan must be input. Values for airflow and fan W/CFM information may be available from the HVI directory at the following URL.

https://www.hvi.org/proddirectory/CPD_Reports/section_1/index.cfm

If HVI does not list fan energy for the installed model, use information from the manufacturer's published documentation. When fan energy is listed as CFM/W instead of W/CFM, it is necessary to invert the value to provide W/CFM as input to the compliance software (for example: 4 CFM/ W = 1/4 W/CFM = 0.25 W/CFM). Installation of a dwelling unit ventilation system with a fan watt draw greater than 1.2 W/CFM of ventilation airflow will affect the results of the performance compliance calculation. Values less than 1.2 W/CFM are compliance-neutral (standard design = proposed design).The compliance software will simulate dwelling unit ventilation using the ventilation system CFM and W/CFM for the proposed design. If the builder specifies a system with heat recovery, he or she inputs the recovery efficiency of the proposed system, and the compliance software uses it in the proposed design to calculate the heat recovery effect of the dwelling unit ventilation. Ventilation heat recovery is never used in the standard design.

4.6.7    Local Exhaust (Section 5 of ASHRAE 62.2)

From ASHRAE 62.2 - Table 5-1 Demand-Controlled Local Ventilation Exhaust Airflow Rates.

From ASHRAE 62.2 - TABLE 5.2 Continuous Local Ventilation Exhaust Airflow Rates

Local exhaust (sometimes called spot ventilation) has long been required for bathrooms and kitchens to remove moisture and odors at the source. Building codes have required an operable window or an exhaust fan in bathrooms for many years and have generally required kitchen exhaust either directly through a fan or indirectly through a recirculating range hood and an operable window. The Energy Standards recognize the limitations of these indirect methods of reducing moisture and odors and requires that these spaces be mechanically exhausted directly to outdoors, even if windows are present. Moisture condensation on indoor surfaces are a leading cause of mold and mildew in buildings. The occurrence of asthma is also associated with high interior relative humidity. Therefore, it is important to exhaust the excess moisture from bathing and cooking directly at the source.

The Energy Standards require that each kitchen and bathroom have an exhaust fan. Generally, this will be a dedicated exhaust fan in each room that requires local exhaust, although ventilation systems that exhaust air from multiple rooms using a duct system connected to a single exhaust fan are allowed as long as the minimum local exhaust requirement is met in all rooms served by the system. The standards define kitchens as any room containing cooking appliances, and bathrooms any room containing a bathtub, shower, spa, or other similar source of moisture. A room containing only a toilet is not required to have an exhaust fan; ASHRAE 62.2 assumes there is an adjacent bathroom with local exhaust.

Building codes may require that fans used for kitchen range hood exhaust ventilation be safety-rated by UL or some other testing agency for the particular location and/or application. Typically, these requirements address fire safety issues of fans placed within an area defined by a set of lines at 45° outward and upward from the cooktop. Few bathroom exhaust fans will have this rating, so they cannot be used in these locations.

4.6.7.1    Demand-Controlled (Intermittent) Local Exhaust

The Energy Standards require that local exhaust fans be designed to be operated by the occupant. This usually means that a wall switch or some other control is accessible and obvious. There is no requirement to specify where the control or switch needs to be located, but bathroom exhaust fan controls are generally located next to the light switch, and kitchen exhaust fan controls are generally integrated into the range hood or mounted on the wall or counter adjacent to the range hood.

Bathrooms can use a variety of exhaust strategies. They can use ceiling-mounted exhaust fans or may use a remotely mounted fan ducted to two or more exhaust grilles. Demand-controlled local exhaust can be integrated with the dwelling unit ventilation system to provide both functions. Kitchens can have range hood exhaust fans, down-draft exhausts, ceiling- or wall-mounted exhaust fans, or pickups for remote-mounted inline exhaust fans. Generally, HRV/ERV manufacturers do not allow exhaust ducting from the kitchen because of the heat, moisture, grease, and particulates that should not enter the heat exchange core. Building codes require kitchen exhaust fans to be connected to metal ductwork for fire safety.

A.   Control and Operation for Intermittent Local Exhaust

The choice of control is left to the designer. It can be a manual switch or automatic control like an occupancy sensor. Some exhaust fans have multiple speeds, and some fan controls have a delay-off function that operates the exhaust fan for a set time after the occupant leaves the bathroom. New control strategies continue to come to the market. The only requirement is that there is a control. Title 24, Part 11 may specify additional requirements for the control and operation of intermittent local exhaust.

B.   Ventilation Rate for Demand-Controlled Local Exhaust

A minimum exhaust airflow of 100 CFM is required for vented kitchen range hoods, and 300 CFM or 5 ACH is required for other kitchen exhaust fans. A minimum exhaust airflow of 50 CFM is required for bathroom fans.

The 100 CFM requirement for the range hood or microwave/hood combination is the minimum to adequately capture the moisture, particulates, and other products of cooking and/or combustion. Only in kitchens that are enclosed, the exhaust requirement can also be met with either a ceiling or wall-mounted exhaust fan or with a ducted fan or ducted ventilation system that can provide at least five air changes of the kitchen volume per hour. Recirculating range hoods that do not exhaust pollutants to the outside cannot be used to meet the requirements of ASHRAE Standard 62.2 unless paired with an exhaust system that can provide at least five air changes of the kitchen volume per hour.

The 2019 Title 24 Part 6 standards require verification that range hoods are HVI-certified to provide at least one speed setting at which they can deliver at least 100 CFM at a noise level of 3 sones or less. Verification must be in accordance with the procedures in Reference Residential Appendix RA3.7.4.3. Range hoods that have a minimum airflow setting exceeding 400 CFM are exempt from the noise requirement. HVI listings are available at:

https://www.hvi.org/proddirectory/CPD_Reports/section_1/index.cfm

ASHRAE Standard 62.2 limits exhaust airflow when atmospherically vented combustion appliances are located inside the pressure boundary. This is particularly important to observe when large range hoods are installed. Refer to Section 4.6.8.4 below for more information.

4.6.7.2    Continuous Local Exhaust

The Energy Standards allow the designer to install a local exhaust system that operates without occupant intervention continuously and automatically during all occupiable hours. Continuous local exhaust is generally specified when the local exhaust ventilation system is combined with a continuous dwelling unit ventilation system. For example, if the dwelling unit ventilation is provided by a continuously operating exhaust fan located in the bathroom, this fan may also satisfy the local exhaust requirement for that bathroom, provided the fan provides airflow greater than or equal to the minimum continuous local ventilation airflow rate. Continuous local exhaust may also be part of a pickup, or an interior grille, for a remote fan or HRV/ERV system.

Continuously operating bathroom fans must operate at a minimum of 20 CFM. Continuously operating kitchen fans are permitted only for enclosed kitchens. Refer to Tables 5.1 and 5.2 in ASHRAE 62.2 for other local demand controlled and continuous exhaust requirements.

4.6.8    Other Requirements (Section 6 of ASHRAE 62.2)

4.6.8.1    Adjacent Spaces and Transfer Air

ASHRAE Standard 62.2 requires that the air used for ventilation come from the outdoors. Air may not be drawn in as transfer air from other spaces that are outside the occupiable space of the dwelling unit, or from between dwelling units and corridors. This is to prevent airborne pollutants originating in those other spaces from contaminating the dwelling unit. For example, drawing ventilation air from the garage could introduce VOCs or pesticides into the indoor air. Drawing ventilation air from an unconditioned crawlspace could cause elevated allergen concentrations in the dwelling such as mold spores, insects, or rodent allergens. Likewise, drawing air from an adjacent dwelling could introduce unwanted contaminants such as cooking odors or cigarette smoke.

Standards §150.0(o)1E requires HERS verification compliance with a maximum of 0.3 CFM/ft² dwelling unit enclosure leakage when either supply ventilation is used or exhaust ventilation is used. The protocol for the blower door test is given in Reference Residential Appendix RA3.8. See also Section 4.6.3.2 in this chapter for more information about multifamily dwelling unit compartmentalization.

In addition to designing the ventilation system to draw air from the outdoors, the standard also requires that measures be taken to prevent air movement between adjacent dwelling units and between the dwelling unit and other nearby spaces, such as garages. The measures can include air sealing of envelope components, pressure management, and use of airtight recessed light fixtures. The measures must apply to adjacent units above and below, as well as side by side.

Air sealing must include pathways in vertical components such as demising walls and walls common to the unit and an attached garage, and in horizontal components such as floors and ceilings. Pipe and electrical penetrations are examples of pathways that require sealing.

4.6.8.2    Instructions and Labeling

Field studies have shown that switches for exhaust fans do not have the required labels, and that many homeowners do not understand the importance of continuous operation of the ventilation fans for maintaining indoor air quality. Standards Section §10-103(b)4 require the builder to leave in the building, for the building owner at occupancy, a description of the quantities of outdoor air that the ventilation system(s) are designed to provide to the conditioned space of the building and instructions for proper operation and maintenance of the ventilation system.

Because the concept of a designed dwelling unit ventilation system may be new to many occupants, the standards section requires that ventilation system controls be labeled as to function. One acceptable option is to affix a label to the electrical panel that provides some basic system operation information.

4.6.8.3    Clothes Dryers

All laundry rooms must be built with a duct to the outdoors, designed to be connected to the dryer. Devices that allow the exhaust air to be diverted into the indoor space to provide extra heating are not permitted. This requirement is consistent with existing clothes dryer installation and design standards.

In multifamily buildings, multiple dryer exhaust ducts can be connected to a common exhaust only when dampers are provided to prevent recirculation of exhaust air from one apartment to another.

4.6.8.4    Combustion and Solid-Fuel Burning Appliances

ASHRAE Standard 62.2 requires that the vent system for combustion appliances be properly installed, as specified by the instructions from the appliance manufacturer and by the California Building Code. Compliance with the venting requirements will involve determining the type of vent material to be used, the sizing of the vent system, and vent routing requirements.

ASHRAE Standard 62.2 includes a provision intended to prevent back drafting, where one or more large exhaust fans are installed in a home with atmospherically vented or solid fuel appliances. If the two largest exhaust fans have a combined capacity that exceeds 15 CFM/100 ft² of floor area, then makeup air must be provided. This provision applies only when the atmospherically vented appliance is inside the pressure boundary of the house and does not include a summer cooling fan that is designed to be operated with the windows open. Direct-vent appliances are not considered “atmospherically vented.”

The two largest exhaust fans are normally the kitchen range hood and the clothes dryer (if located inside the dwelling unit pressure boundary). Large-range hoods, particularly downdraft range hoods, can have capacities of 1,000 CFM or more.

A problem with this requirement can be solved in one of three ways. First, all atmospherically vented combustion appliances can be moved outside the pressure boundary of the house (to the garage or other similar space). Second, the flow rate of one or more of the fans can be reduced so that the combined flow is less than 15 CFM/100 ft². Finally, makeup air can be provided to offset the net exhaust rate.

4.6.8.5    Garages

Garages often contain numerous sources of contaminants. These include vehicle exhaust, gasoline, pesticides, paints and solvents, and others. The Energy Standards require that when garages are attached to the house, these contaminants be prevented from entering the house. The wall between the unit and garage (or garage ceiling in designs with living space above garages) shall be designed and constructed so that no air migrates through the wall or ceiling. The common doors and any air handlers or ducts located in the garage shall also be sealed, weatherstripped, or gasketed.

Standards §150.0(o) specifies that compliance with ASHRAE 62.2 Section 6.5.2 (Space Conditioning System Ducts) shall not be required. However, the applicable duct leakage verification requirements are given in Standards Sections 150.0(m)11 for newly constructed buildings, and 150.2(b)iD for alterations to systems in existing buildings. All ducted space conditioning systems in newly constructed buildings are required to pass HERS verification that duct system leaks are less than or equal to 5 percent of the system airflow rate. This requirement applies to portions of the system that may be in a garage space.

For alterations to space conditioning systems in existing buildings that have all or portions of the forced air ducts, plenums or air-handling units in the garage, Section 150.2(b)1D specifies two compliance approaches:

1.   The measured system duct leakage shall be less than or equal to 6 percent of system air handler airflow as determined using the procedures in Reference Residential Appendix Section RA3.1.4.3.1.

2.   All accessible leaks located in the garage space shall be sealed and verified through a visual inspection and a smoke test by a certified HERS Rater using the methods specified in Reference Residential Appendix RA3.1.4.3.5.

For additions and alterations to existing buildings, any length of new or altered duct located in the garage or any new or altered air-handling unit located in the garage triggers these duct leakage testing requirements.

4.6.8.6    Ventilation Opening Area

The dwelling unit mechanical ventilation is intended to provide adequate ventilation to typical new homes under normal circumstances. On occasion, however, houses experience unusual circumstances where high levels of contaminants are released into the space. When this occurs, a means of providing the significantly higher levels of ventilation required to remove the contaminants is needed. Operable windows are the most likely means of providing the additional ventilation.

This section of ASHRAE Standard 62.2 requires ventilation openings in habitable spaces, toilets, and utility rooms. Ventilation openings usually mean operable windows, although a dedicated nonwindow opening for ventilation is acceptable. Spaces that meet the local exhaust requirements are exempted from this requirement.

4.6.8.7    Habitable Spaces

Habitable spaces are required to have ventilation openings with openable area equal to at least 4 percent of the space floor area (but not less than 5 ft²). Dining rooms, living rooms, family rooms, bedrooms, and kitchens are considered habitable space. Closets, crawl spaces, garages, and utility rooms are generally not. If the washer and dryer are located in an open basement that is also the family room, it would be considered habitable space.

The openings do not have to be provided by windows. They can also be provided by operable, insulated, weather-stripped panels.

Ventilation openings, which include operable windows, skylights, through-the-wall vents, window vents, or similar devices, shall be readily accessible to the occupant. This means that the occupant must be able to operate the opening without having to climb on anything. An operable skylight must have some means of being operated while standing on the floor: a push rod, a long crank handle, or an electric motor.

If a ventilation opening is covered with louvers or otherwise obstructed, the openable area is the unobstructed free area through the opening.

4.6.8.8    Minimum Filtration

Compliance with ASHRAE 62.2 Sections 6.7 (Minimum Filtration) and 6.7.1 (Filter Pressure Drop) are not be required (Standards §150.0(o)1D). However, air filtration for mechanical systems must conform to the specifications in Standards Section 150.0(m)12. Information on air filtration requirements is given in Section 4.4.1.14 of this chapter.

4.6.8.9    Air Inlets

When the ventilation system is designed with air inlets, the inlets must be located away from locations that can be expected to be sources of contamination. The minimum separation is 10 ft. Inlets include not only inlets to ducts, but windows that are needed to the opening area.

The Energy Standards list some likely sources of contaminants. For typical residential applications, the sources will include:

1.  Vents from combustion appliances.

2.  Chimneys.

3.  Exhaust fan outlets.

4.  Barbeque grills.

5.  Locations where vehicles may be idling for any significant length of time.

6.  Any other locations where contaminants will be generated.

The Energy Standards also require that air intakes be placed so that they will not become obstructed by snow, plants, or other material. Forced air inlets must also be equipped with insect/rodent screens, where the mesh is no larger than 1/2 inch.

4.6.9    Air-Moving Equipment (Section 7 of ASHRAE 62.2)

Equipment used to meet the dwelling unit ventilation requirements or the local exhaust ventilation requirements shall be rated to deliver the required airflow and shall have sound ratings that meet the requirements of this section.

4.6.9.1    Selection and Installation

ASHRAE Standard 62.2 requires that equipment used to comply with the standard be selected based on tested and certified ratings of performance for airflow and sound. When selecting fans for use in meeting the requirements of the standard, you must check the Home Ventilating Institute (HVI) Certified Products Directory to confirm that the equipment you select has been tested and the rated performance meets the requirements. The HVI-Certified Products Directory can be viewed at the following URL:

http://www.hvi.org/proddirectory/index.cfm.

In addition, the Energy Standards require that the fans be installed in accordance with the manufacturer’s instructions. You must review the installation instructions and other literature shipped with the fan and make sure that the installation complies with those instructions.

4.6.9.2    Sound Ratings for Fans

Standards §150.0(o)1G requires kitchen range hoods to be rated for sound in accordance with Section 7.2 of ASHRAE 62.2, and provides an exception to allow kitchen range hoods to be rated for sound at a static pressure determined at working speed as specified in HVI 916 Section 7.2. The static pressure at working speed may be lower than 0.1 inch w.c.

One common reason ventilation equipment may not be operated by dwelling unit occupants, particularly local exhaust fans, is the noise the fans may create. To address this, ASHRAE Standard 62.2 requires that certain fans be rated for sound and that installed fans shall have ratings below specified limits. The sound rating must be done at an airflow that is no less than the airflow that the fan must provide to meet the ventilation airflow requirement.

Because of the variables in length and type of duct and grille, there is no clearly repeatable way to specify a sound level for ventilation devices that are not mounted in the ceiling or wall surface. Consequently, air handlers, HRV/ERVs, inline fans, and remote fans are exempted from the sound rating requirements that apply to surface-mounted fans. However, to reduce the amount of fan and/or motor noise that could come down the duct to the grille, the Energy Standards sets a minimum of 4 feet of ductwork between the grille and the ventilation device. This may still produce an undesirable amount of noise for the occupant, especially if hard metal duct is used. Flexible insulated duct or a sound attenuator will reduce the transmitted sound into the space.

A.   Continuous Ventilation Fans (Surface-Mounted Fans)

Continuously operated fans shall be rated at 1.0 sone or less. This 1.0 sone requirement applies to continuous dwelling unit ventilation fans and to continuous local exhaust ventilation fans.

B.   Intermittent or Demand Controlled Fans (Surface-Mounted Fans)

Intermittently operated dwelling unit ventilation fans shall be rated at a maximum of 1.0 sone. Demand-controlled local exhaust fans shall be rated at a maximum of 3.0 sones, unless the maximum rated airflow is greater than 400 CFM.

ASHRAE Standard 62.2 extends the requirement for quiet fans to include range hoods and bath exhaust fans, not just dwelling unit ventilation system fans. Dwelling unit ventilation fans or systems that operate continuously must be rated 1.0 sone or less, but demand-controlled local exhaust fans, including demand-controlled bathroom fans, must be 3.0 sones or less. Range hood exhaust fans must also be rated at 3.0 sones or less at the minimum required speed of 100 CFM.

4.6.9.3    Airflow Measurements and Airflow Ratings

All dwelling unit ventilation systems must demonstrate compliance by direct measurement of airflow using a flow hood, flow grid, or other approved measuring device. HERS verification of dwelling unit ventilation airflow is required for newly constructed buildings and existing buildings with additions greater than 1,000 square feet or an increase in the number of dwelling units.

There are two ways to demonstrate compliance with airflow requirements for local exhaust ventilation:

1.  Test the ventilation system using an airflow measuring device after completion of the installation to confirm that the delivered ventilation airflow meets the requirement.

2.  Conformance to a prescriptive requirement that the fan has a certified airflow rating that meets or exceeds the required ventilation airflow, and ventilation ducts meet either the fan manufacturer’s published duct design specifications or the prescriptive duct design requirements given in Table 4-16 (Table 5.3 of ASHRAE 62.2).

When using the prescriptive duct sizing table or manufacturer's design criteria for compliance, the certified airflow rating of the fan must be based on tested performance at the 0.25 inches water column (w.c.) static pressure. The airflow rating of a fan is available from the Home Ventilating Institute (HVI) Certified Products Directory at the HVI website (www.hvi.org).

If the manufacturer's duct system design specifications are used for compliance, the enforcement agency may require that the manufacturer's published system design documentation be provided for use for inspection of the installation(s).

The prescriptive duct design criteria given in Table 4-15 provide maximum exhaust duct lengths based on duct type and diameter. The higher the airflow, the larger in diameter or shorter in length the duct must be. Smooth duct can be used to manage longer duct runs. Interpolation and extrapolation of Table 4-15 are not allowed. For airflow rates not listed, use the next higher value. The table is not applicable for systems with airflow greater than 125 CFM at 62 Pa (0.25 inches water column) static pressure.

Table 4-15: Prescriptive Duct Sizing for Single-Fan Exhaust Systems
(ASHRAE 62.2, Table 5.3)

a. For noncircular ducts, calculate the diameter as four times the cross-sectional area divided by the perimeter.

b. This table assumes no elbows. Deduct 15 ft (5 m) of allowable duct length for each elbow.

c. NL = no limit on duct length of this size.

d. X = not allowed; any length of duct of this size with assumed turns and fitting will exceed the rated pressure drop.

4.6.9.4    Exhaust Ducts

ASHRAE Standard 62.2 contains restrictions on situations where multiple exhausts are connected through a combined duct system. These restrictions are intended to prevent air from moving between spaces through the exhaust ducts.

The first restriction is that if more than one exhaust fan in a dwelling shares a common duct, then each fan must be equipped with a backdraft damper so that air exhausted from one bathroom or unit is not allowed to go into another space. Exhaust fans in multiple dwelling units may not share a common duct.

The other restriction applies to remote fans serving more than one dwelling unit. Sometimes a single remote fan or HRV/ERV will exhaust air from several dwelling units in a multifamily building. This section requires that either the shared exhaust fan operate continuously or each unit be equipped with a backdraft damper so that air cannot flow from unit to unit when the fan is off.

In multifamily buildings, fire codes may impose additional restrictions.

4.6.9.5    Supply Ducts

Supply outlets to more than one dwelling unit may be served by a single fan upstream of all the supply outlets if the fan is designed to run continuously or if each supply outlet is equipped with a backdraft damper to prevent cross-contamination when the fan is not running.