4.6 Indoor Air Quality and Mechanical Ventilation    

As houses have been tightened up over the last several years due to rising energy cost and the availability of higher performing building materials, normal infiltration and exfiltration have significantly reduced. This condition has increased the effect of contaminants and pollutants introduced through common building materials, cleaners, finishes, packaging, furniture, carpets, clothing, and other products. The Energy Standards have always assumed adequate indoor air quality would be provided by a combination of infiltration and natural ventilation and that home occupants would open windows as necessary to make up any shortfall in infiltration. However, Energy Commission-sponsored research on houses built under the 2001 Standards revealed that overall ventilation rates are lower than expected, indoor concentration of chemicals such as formaldehyde are higher than expected, and many occupants do not open windows regularly for ventilation. The 2013 Standards included mandatory mechanical ventilation intended to improve indoor air quality (IAQ) in homes. The 2016 Energy Standards continue this effort.

As specified by §150.0(o), all low-rise residential buildings must meet the requirements of ASHRAE Standard 62.2-2010, including Addenda b, c, e, g, h, i, j, l, and n to ASHRAE 62.2-2010. The exception is that opening and closing windows and continuous operation of central fan-integrated ventilation systems are not allowable options for meeting whole-building ventilation requirements.

The requirements of ASHRAE Standard 62.2 focus on whole-building mechanical ventilation and local ventilation exhaust at known sources of pollutants or moisture, such as kitchens, baths, and laundries. While not required by the Energy Standards, builders and homeowners should select materials, finishes, and furnishings that have no or low emissions of air pollutants, such as formaldehyde and volatile organic compounds (VOCs), because keeping air pollutants out of the building in the first place is more effective than flushing them out later through ventilation.

Most building materials emit some level of VOCs, formaldehyde, or other pollutants, and the resultant indoor pollutants can pose a substantial risk to occupant health. Pollutant emissions are highest immediately after a new product is installed, but emissions may continue for days, weeks, months, or years. Buildup of these air pollutants in the home is affected by ventilation, infiltration, and filtration rates; thus, these rates are addressed by the requirements in ASHRAE Standard 62.2.

The California Air Resources Board (ARB) provides guidance for reducing indoor air pollution in homes. For more information, see the ARB Indoor Air Quality Guidelines:

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.

Compliance with the whole-building ventilation airflow specified in ASHRAE 62.2 is required in new buildings and in buildings with additions greater than 1,000 ft². All other mechanical ventilation requirements, including local exhaust, must be met (as applicable) in all additions and alterations. 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). Individual dwelling units in multifamily buildings are required to each meet the same requirements as single-family dwelling units, except as otherwise described in Section 4.6.8.

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

1.    A whole-building mechanical ventilation system shall be provided. The typical solutions are described in the 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 systems vented to the outdoors.

3.    Clothes dryers shall be vented to the outdoors.

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

1.    Ventilation air shall come from outdoors and shall not be transferred from adjacent dwelling units, garages, 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.    The walls and openings between the house and the garage shall be sealed.

5.    Habitable rooms shall have windows with a 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 6 filters or better and be designed to accommodate the system's air filter media rated pressure drop for the system design airflow rate.

7.    Dedicated air inlets (not exhaust) that are part of the ventilation system design shall be located away from known 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 whole-building ventilation requirement and the local ventilation exhaust requirement shall be rated in terms of airflow and sound:

a.  All continuously operating fans shall be rated at a maximum of 1.0 sone.

b.  Intermittently operated whole-building ventilation fans shall be rated at a maximum of 1.0 sone.

c.  Intermittently operated local exhaust fans shall be rated at a maximum of 3.0 sone.

Remotely located air-moving equipment (mounted outside habitable spaces) need not meet sound requirements if there is at least 4 feet of ductwork between the fan and the intake grille.

4.6.1                                                                                                                   Compliance and Enforcement

Compliance with ASHRAE 62.2 requirements must be verified by the enforcement agency, and the whole-building ventilation airflow rate must be verified by a HERS Rater in accordance with the procedures in Residential Appendix RA3.7. The applicable certificates of compliance, installation, and verification must be registered with an approved HERS Provider.

If a central heating/cooling system air-handler fan is used to ventilate the dwelling (central fan integrated 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 performance of the air handler.

4.6.1.1      Certificate of Compliance Reporting Requirements:

When the performance compliance approach is used, the required whole-building ventilation airflow is calculated based on the total conditioned floor area (CFA) and the number of bedrooms. (See Section 4.6.3.1A.) Therefore, it is important that these values are input into the compliance software correctly and checked by the plans examiner. The performance certificate of compliance (CF1R) will report:

the Required ventilation airflow rate (calculated value) that must be delivered by the system.

System type selected (that is, exhaust, supply, balanced, CFI).

Fan power ratio (watts/CFM) for the selected system.

The requirement of HERS verification of fan watt draw for the air handler when a CFI ventilation system is being used.

The installed whole-building ventilation system must conform to the performance requirements on the CF1R. For more information about the performance calculations for whole-building ventilation systems, see Section 4.6.4. There are no requirements to describe fans installed for other purposes such as local exhaust on the performance CF1R.

When using the prescriptive compliance approach, information that describes the whole-building ventilation system is not required on the CF1R. Unless otherwise required by the enforcement agency, calculation of the required ventilation airflow rate and selection of the system type can be done at installation. There are no requirements to describe fans installed for other purposes, such as local exhaust, on the prescriptive 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 a certificate of installation (CF2R-MCH-27) for the dwelling. The HERS Rater must complete a certificate of verification (CF3R-MCH-27) for the dwelling.

The following information must be provided on the CF2R-MCH-27 and CF3R-MCH-27 to document compliance with §150.0(o):

Required whole-building ventilation airflow rate for continuous or intermittent operation as specified by ASHRAE 62.2 equations. (See Section 4.6.3.)

Installed system type (that is, exhaust, supply, balanced, CFI).

Measured airflow rate of the installed whole-building ventilation system.

Confirmation from the builder/installer that the other applicable requirements given in ASHRAE 62.2 have been met. (See Sections 4.6.5) and 4.6.6.)

4.6.2                                                                                                                   Typical Solutions for Whole-Building Ventilation

There are three typical solutions for meeting the outside air ventilation requirement:

1.    Exhaust ventilation.

2.    Supply ventilation.

3.    Combination of supply and exhaust ventilation. (If the supply and exhaust flows are within 10 percent of each other, this is called a “balanced ventilation system”.)

Whole-building ventilation may be achieved through a single fan or a system of fans that are dedicated to whole-building ventilation only or by fans that also provide local exhaust or distribute heating and cooling.

4.6.2.1     Exhaust Ventilation

Figure 4-28: Exhaust Ventilation Example

Source: California Energy Commission

Exhaust ventilation is usually achieved by a quiet ceiling-mounted bath fan or remote-mounted inline or exterior-mounted fan. Air is drawn from the house by the exhaust fan and outdoor air enters the house through infiltration.

Many high quality bath fans are available in the 30 to 150-cfm size range are quiet enough to be used continuously. One or more fans of this size will meet the requirements of most homes. The exhaust fan can be a dedicated IAQ fan or a typical bath fan that is used for both whole-building ventilation and local ventilation.

Inline fans (either single pickup or multipoint pickup) can be a very effective method of providing quiet exhaust ventilation from one or several bathrooms. Inline fans can be located in the garage, attic, basement, or mechanical room.

Exterior-mounted fans can be mounted on the exterior wall or on the roof. A sound rating is not required for remote or exterior fans with at least 4 ft of duct between the closest pickup grille and the fan.

4.6.2.2     Supply Ventilation

Figure 4-29: Supply Ventilation Example

Source: California Energy Commission

Supply ventilation works by bringing outside air into the house through a dedicated supply fan or the central forced-air system air handler and escapes through exfiltration.

The air handler or supply the outdoor air inlet should avoid areas  contaminants, such as garages, barbeque areas, and chimneys. If a dedicated fan is used, care must be taken to avoid introducing too much outdoor air into one location and creating uncomfortable conditions. The ventilation air can be distributed by a dedicated duct system separate from the central forced air distribution duct system.

Alternatively, the central forced-air system air handler can be configured to function as a ventilation supply system by installing a dedicated ventilation air duct that connects to the return plenum of the air handler and to the dwelling exterior. This strategy, called central fan integrated (CFI) ventilation, uses negative pressure in the return plenum to pull outdoor air in through the ventilation air duct and into the return plenum, then the central system air handler distributes the ventilation air through the house. A damper and controls must be installed that ensure the air handler delivers the required ventilation airflow regardless of the size of the heating or cooling load.

When considering design and compliance for CFI ventilation systems, it is important to distinguish between the central forced-air system fan total airflow and the much smaller ventilation airflow (the airflow that is induced to flow into the return plenum from outdoors). Refer to Figure 4-29 and note that the total airflow through the air handler is the sum of the return airflow and the ventilation airflow.

ASHRAE Standard 62.2, Section 4.3 requires the installer to measure the ventilation airflow rate in a CFI system in all operation modes to ensure that it will meet the ventilation rate requirements, regardless of whether the system operates to provide heating or cooling. Because §150.0(o) specifically prohibits continuously operating the central forced air system with CFI ventilation systems, CFI systems must be intermittent. The results of the airflow measurement of the installed CFI system and the intermittent ventilation control schedule used for the CFI system must be given on the Certificate of Installation. The whole-house ventilation rate must also be verified by a HERS Rater.

The outside air (OA) ducts for CFI ventilation systems cannot be sealed/taped off during duct leakage testing. However, CFI OA ducts that use controlled motorized dampers that open only when OA ventilation is required and close when OA ventilation is not required may be closed during duct leakage testing.

CFI ventilation systems can use a very significant amount of electricity annually. Air handlers used in CFI ventilation systems are required to meet the prescriptive fan watt draw requirements in all climate zones.

4.6.2.3     Combination Ventilation

Figure 4-30: Combination Ventilation Example

Source: California Energy Commission

Combination systems use both exhaust fans and supply fans. If both fans supply the same airflow, the system is balanced, and the house has a neutral pressure.

Combination systems are often integrated devices, sometimes with a heat exchanger or heat recovery wheel. The supply and exhaust airstreams are typically of equal flow.

Combination systems can also be a mixture of supply fans and exhaust fans. It may be as simple, such as a quiet continuous bathroom exhaust fan matched to an outdoor air connection that introduces air into the return air plenum of a continuously operating central heating/cooling system air handler.

Note: Ventilation systems that constantly operation the central heating/cooling system air handler can use a very significant amount of electricity annually and are not permitted by the Energy Standards.

4.6.3                                                                                                                   Whole-Building Ventilation Flow Rate (Section 4 of ASHRAE 62.2)    

The whole-building ventilation system may operate continuously or intermittently. The whole-building ventilation rate is determined for continuous ventilation: if the system is operated intermittently, an adjustment is made.

4.6.3.1     Continuous Whole-Building Ventilation

There are two strategies for determining the continuous whole-building ventilation rate: the fan ventilation rate method, which assumes that all required ventilation will be provided mechanically, and the total ventilation rate method, which assumes that ventilation will be achieved by a combination of natural infiltration and mechanical ventilation.

Both methods are allowed for newly constructed homes and alterations. The fan ventilation rate method may be advantageous from a design perspective because the infiltration rate of the house does not need to be determined before construction. In either case, a fan system must be designed and installed that meets the whole-building ventilation airflow requirements, however it is determined.

A.   Fan Ventilation Rate Method

The continuous whole-building ventilation rate is 1 cfm for each 100 ft² of conditioned floor area plus 7.5 cfm for each occupant. The number of occupants is calculated as the number of bedrooms plus one. For example, a three bedroom house is assumed to have four occupants. The required ventilation rate is given by the following Equation 4-1.

Equation 4-1

Where:

Instead of using one of the equations given above, Table 4-14 may be used to determine the required ventilation. This table allows the user to find the required ventilation rate directly if he or she knows the floor area and number of bedrooms.

To comply with ASHRAE 62.2 the delivered airflow of the whole house ventilation fan must be greater than or equal to the required ventilation rate (cfm) from either Table 4-14 or Equation 4-1.

Table 4-14 –: Continuous Whole-Building Ventilation Rate (cfm) (from ASHRAE 62.2, Table 4.1a (I-P))

Source: ASHRAE 62.2

A.      Total Ventilation Rate Method

This method for determining a continuous whole-building ventilation rate starts with calculating the total ventilation rate, which consists of both the natural and mechanical ventilation rates.

The total ventilation rate is calculated using an equation similar to that used in the fan ventilation rate method. Next, the natural ventilation (infiltration) rate is calculated from diagnostically tested values.

The infiltration rate is subtracted from the total ventilation rate, leaving the ventilation rate that must be provided mechanically.

The equation for calculating the total ventilation rate is:

Equation 4-2

Where:

2)

The number multiplied times the floor area is three times greater than that used in Equation 4-1.

The ventilation rate associated with infiltration is calculated using an effective leakage area (ELA) value that must be diagnostically verified in the field.

The ELA value used for these equations is in square feet, not square inches as may be the case in other equations.

RA3.8 covers the protocols for blower door testing for verifying infiltration for reduced infiltration compliance credit. Unless specifically directed otherwise in this section, RA3.8 shall be met.

Because infiltration can occur by air coming into the home as well as air going out of the home, it is more accurate to measure ELA under depressurization and pressurization (using a 4 Pa reference pressure), then average the two values using Equation 4-3.

Equation 4-3

Where:

2)

2)

2)

When designing for a house that is not built yet, the ELA values will be estimated numbers. If the actual (measured) number is different, the ventilation system design may need to be modified to comply.

The leakage is normalized based on the area of the house and the potential for stack effect using Equation 4-4.

Equation 4-4

Where:

2)

2)

The effective annual infiltration rate is then calculated using Equation 4-5. This is the amount of infiltration that is considered to offset the need for fan-powered ventilation.

Equation 4-5

Where:

2)

The ventilation rate required by the fan is then calculated by subtracting the infiltration ventilation rate from the total ventilation rate.

Equation 4-6

Where:

For well-sealed houses, the fan ventilation rate calculated using the total ventilation rate method may be higher than that calculated by the fan ventilation rate method, so it is worth checking both.

No whole-building ventilation is required if

C.          Ventilation Rate for Combination Systems

When a combination ventilation system is used, meaning that both supply and exhaust fans are installed, the provided ventilation rate is the larger of the total supply airflow or the total exhaust airflow. The airflow rates of the supply and exhaust fans cannot be added together to determine the provided ventilation rate.

4.6.3.2      Intermittent Whole-Building Ventilation

In some cases, it may be desirable to design a whole-building ventilation system that operates intermittently. One common example of intermittent ventilation is when outside air is ducted to the return plenum of the central heating/cooling system, and thus the central heating/cooling system fan is used to distribute the ventilation air to the rooms in the building (See CFI system described above in the supply ventilation section).

Intermittent mechanical ventilation systems, devices, or controls may be approved for use for compliance with the HERS field verification requirements for whole-building mechanical ventilation airflow. A listing of certified intermittent mechanical ventilation systems is posted at the following URL.

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

Intermittent ventilation is permitted as long as the ventilation airflow is increased to respond to the fewer hours of fan operation and the tendency of pollutant concentrations to build up during off cycles.

Equation 4-7

Where:

To obtainTable 4-15, the required turnover,

Equation 4-8

Where

Table 4-14 or Equation 4-1(cfm)

2)

The maximum allowable

To obtain

Table 4-15 –: Mechanical Ventilation Effectiveness for Intermittent Fans

Source: ASHRAE 62.2

Intermittent 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 10 percent of the time and that a single on/off cycle occurs at least once per day.

ASHRAE 62.2 requires that the ventilation system have an override control that is readily accessible to the occupants. The control must be capable of being accessed quickly and easily by the occupants without having to remove panels or doors. It can be a labeled wall switch by 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 the inside the fan. The occupant must be able to modify the settings or override the system.

If intermittent fans are used, they must be controlled by a timer, and they must have an increased airflow rate to compensate for the off time.

Time-of-day timers or duty cycle timers can be used to control intermittent whole-building 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 air handler has already operated for heating or cooling before it turns on the air handler for ventilation only operation.

4.6.4                                                                                                                   Whole-Building Mechanical Ventilation Energy Consumption    

For builders using the performance compliance approach, the energy use of fans (other than CFI fans) installed to meet the whole-building 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 whole-building ventilation system airflow rate is set equal to the proposed design whole-building ventilation system airflow rate, so there is no energy penalty or credit for most systems. Systems that use heat recovery or energy recovery ventilators (HR/ERV) may need to account for the heat recovery benefit in the performance calculation to make up for the high energy use.

The energy use of the central air handler fan 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. CFI systems are the only type of ventilation system that must meet a prescriptive fan watt draw requirement that must be tested by the builder/installer and verified by a HERS Rater in accordance with the diagnostic test protocols given in RA3.3

Energy use of fans installed for other purposes, such as local exhaust, is not regulated in the Energy Standards.

4.6.4.1    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/or distribute ventilation air around the home even when there is no heating or cooling required. CFI systems generally do not operate continuously, thus do not meet the whole-building ventilation requirement as a “continuous" system. 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 very significant amount of electricity annually.

The Energy Standards include mandatory requirements for ducted central cooling system air handlers to comply with maximum fan watt draw targets. The watt draw requirement also applies to any ducted central system air handler used for a CFI system. Compliance with this requirement involves a post construction measurement by the installing contractor of the airflow through the air handler, and the simultaneous measurement of the watt draw of the air handler fan motor. This fan watt draw measurement must be measured by the installer and verified by a HERS Rater. (See Reference Residential Appendix RA3.3.) The central system air handler must be operating in ventilation mode (outdoor air damper is open and ventilation air is 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 0.58 W/CFM.

Builders who use CFI systems and comply using the performance approach have the option of accepting the default value for the central system fan watt draw of 0.8 W/CFM, which does not require a post construction measurement and HERS verification. Alternatively, the builder can specify a lower W/CFM value for compliance, which must be tested and verified by a HERS Rater. In either case the compliance software will check the furnace fan heating and cooling operation every hour, and if the air handler has not been operating for at least 20 minutes during that hour, the software will calculate energy use for operation in CFI mode until 20 minutes of fan operating occurs. The standard design ventilation energy consumption for that hour will be calculated as the extra fan run time at a watt draw of 0.58 W/CFM. The proposed design ventilation energy for that hour will be calculated as the extra fan run time at the watt draw that was specified for compliance, otherwise at the default Watt draw of 0.8 W/CFM.

4.6.4.2  Other Whole-Building Ventilation Systems – Watt Draw

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

Builders who specify other whole-building ventilation systems and comply using the performance approach have the option of accepting the default minimum whole-building ventilation airflow rate and a watt draw value of 0.25 W/CFM which is typical of simple exhaust fans that meet the 1 sone requirement. Otherwise, the airflow rate and fan watt draw of the fan may be input. If the builder installs a whole-building ventilation system that has a fan watt draw specification greater than 1.2 W/CFM of ventilation airflow, then he or she must input the ventilation airflow (CFM) and watt draw (W/CFM) corresponding to the system that he or she proposes to install. The compliance software will simulate whole-building ventilation using the builder’s specified ventilation CFM and W/CFM for the proposed design. For the standard design, the builder’s proposed CFM and 1.2 W/CFM will be used. If the builder specifies a system with heat recovery he inputs the 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 heating and cooling effect of the whole-building ventilation. Ventilation heat recovery is never used in the standard design.

4.6.5                                                                                                                   Local Exhaust (Section 5 of ASHRAE 62.2)    

Local exhaust (sometimes called spot ventilation) has long been required for bathrooms and kitchens to deal with moisture and odors at the source. Building codes have required an operable window or an exhaust fan in baths for many years and have generally required kitchen exhaust either directly through a fan or indirectly through a ventless range hood and an operable window. The Energy Standards recognize the limitations of these indirect methods of providing ventilation to reduce moisture and odors and requires that these spaces be mechanically exhausted directly to outdoors, even if windows are present. As tighter homes with more insulation are built, the relative humidity in the home has increased and the potential for condensation on cool or cold surfaces has increased as well. The presence of moisture condensation has been a leading cause of mold and mildew in both new and existing construction. The occurrence of asthma has also increased as the interior relative humidity has gotten higher. Therefore, it has become more important to remove the moisture from bathing and cooking right at the source.

The Energy Standards require that each kitchen and bathroom have a local exhaust system installed. Generally, this will be accomplished by installing 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 ventilation fan are allowed as long as the minimum local ventilation airflow rate requirement is met in all rooms served by the system. The standards define kitchens as any room containing cooking appliances, and bathrooms are rooms containing a bathtub, shower, spa, or other similar source of moisture. A room containing only a toilet is not required by the Energy Standards to have mechanical exhaust; it assumes that there will be an adjacent bathroom that will have local exhaust.

The Energy Standards allow the designer to choose between intermittent operation or continuous operation for the local exhaust ventilation system. The ventilation rates are different because the ventilation effectiveness of an intermittent operation fan is different than the ventilation effectiveness of a continuous operation fan.

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

4.6.5.1      Intermittent Local Exhaust

The Energy Standards require that intermittent local exhaust fans be designed to be operated by the occupant. This usually means that a wall switch or some other type of control is accessible and obvious. There is no requirement to specify where the control or switch needs to be located, but bath fan controls are generally located next to the light switch, and range hood or downdraft 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 typical ceiling bath fans or may use one or two pickups for remote inline or exterior-mounted fans or heat recovery products. Intermittent local exhaust can be integrated with the whole-building ventilation system to provide both functions. Kitchens can have range hoods, down-draft exhausts, ceiling fans, wall fans, or pickups for remote inline or exterior-mounted fans. Generally, HVR/ERV manufacturers will not allow kitchen pickups to avoid the issue of grease buildup in the heat exchange core. Building codes typically require that the kitchen exhaust must be exhausted through 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 an automatic control like an occupancy sensor or a manual switch. Some products have multiple speeds and some switches have a delay-off function that continues the exhaust fan flow 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 Intermittent Local Exhaust

A minimum intermittent ventilation airflow of 100 cfm is required for the kitchen range hood, and a minimum intermittent ventilation airflow of 50 cfm is required for the bath fan.

The 100 cfm requirement for the range hood or microwave/hood combination is the minimum to adequately capture the moisture and other products of cooking and/or combustion. The kitchen 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 the ASHRAE Standard 62.2 unless paired with an exhaust system that can provide at least five air changes of the kitchen volume per hour.

Most range hoods provide more than one speed, with the high speed at 150 cfm or more – sometimes much more. Range hoods are available that are rated for 1,000 or 1,500 cfm on high speed and are often specified when large commercial-style stoves are installed. Care must be taken to avoid backdrafting combustion appliances when large range hoods are used. Refer to Table 5.1 in ASHRAE 62.2 for intermittent local ventilation exhaust airflow rates and to Section 6.4 in ASHRAE 62.2 for makeup air requirements associated with large exhaust appliances.

4.6.5.2      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 whole-building ventilation system. For example, if the whole-building exhaust is provided by a continuously operating exhaust fan located in the bathroom, this fan satisfies the local exhaust requirement for the bathroom. The continuous local exhaust may also be part of the continuous whole-building ventilation system, such as a pickup for a remote fan or HRV/ERV system.

Continuously operating bathroom fans must operate at a minimum of 20 cfm and continuously operating kitchen fans must operate at five air changes per hour. These continuous ventilation airflow rates are different than the ventilation airflow rates required for intermittent local exhaust. Refer to Table 5.2 in ASHRAE 62.2 for continuous local ventilation exhaust airflow rates.

The requirement that continuous kitchen exhaust fans must provide five air changes per hour is due to the difficulty of a central exhaust to adequately remove contaminants released during cooking from large kitchens, have an open-plan design, or have high ceilings. The only way to avoid a vented kitchen hood is to provide more than five air changes per hour of constant local exhaust ventilation.

4.6.6                                                                                                                   Other Requirements (Section 6 of ASHRAE 62.2)    

4.6.6.1 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 products or cigarette smoke.

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 both 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.

Section 6.1 of ASHRAE 62.2 does not prohibit whole-building exhaust or local exhaust ventilation systems and does not require mechanical systems to maintain pressure relationships with adjacent spaces except as required by Section 6.4 of ASHRAE 62.2.

4.6.6.2     Instructions and Labeling

There has been a history of ventilation systems that worked initially but failed due to lack of information for the occupant or lack of maintenance. ASHRAE Standard 62.2 requires that the installer or builder provide written information on the basic ventilation concept being used and the expected performance of the system. These instructions must include how to operate the system and what maintenance is required.

Because the concept of a designed whole-building ventilation system may be new to many of occupants, the standard requires that ventilation system controls be labeled as to the function. No specific wording is mandated, but the wording must make clear what the control is for and the importance of operating the system. This may be as simple as “Ventilation Control” or might include wording such as “Operate whenever the house is in use” or “Keep on except when gone over 7 days”. If the system is designed to operate with a timer as an intermittent system, the labeling may need to be more detailed. One acceptable option is to affix a label to the electrical panel that provides some basic system operation information.

4.6.6.3       Clothes Dryers

All laundry rooms must be built with a duct to the outdoors, designed to be connected to the dryer. Devices which 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.

4.6.6.4     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 backdrafting 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.

4.6.6.5      Garages

Garages often contain numerous sources of contaminants. These include gasoline and exhaust from vehicles, 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, weather-stripped or gasketed. Use of an exterior door system would address this requirement.

ASHRAE 62.2 Section 6.5.2 requires a system with an air handling unit (furnace) is located in the garage, or return ducts located in the garage (regardless of the air handler location) to meet a sealed and tested ducts criteria. of 6 percent of system airflow.

Leakage testing is mandatory for all forced-air duct systems in newly constructed buildings as specified by §150.0(m)11. For additions and alterations to existing buildings, any length of new or altered duct in the garage, or any new or altered air-handling unit in the garage triggers duct leakage testing requirements for the entire system since §150.2(a) and §150.2(b) require new or altered components to meet all applicable requirements in §150.0(o).

4.6.6.6         Ventilation Opening Area

The whole-building 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.

4.6.6.7         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). Rooms people occupy are considered habitable space. 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 windows, skylights, through-the-wall inlets, window air inlets, 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.

4.6.6.8           Minimum Filtration

ASHRAE Standard 62.2 requires that particulate air filtration of no less than MERV 6 efficiency is installed in any HVAC system having more than 10 ft of ductwork. The particulate filter must be installed such that all the air circulated through the furnace or air handler is filtered before passing through the thermal conditioning portion of the system. In 'addition, the standard requires that the filter be located and installed for easy access and service by the homeowner. The filter must be of a type and size that alows the system to operate at the design airflow rate and at less than the design pressure drop across the filter. Refer to Section 4.4.4.13 for additional information on air filtration requirements.

The filter retainer section must be easily accessible by the homeowner to assure continued monitoring and replacement. The filter bank may be located in the following locations:

1. the air handler/furnace

2. the return air plenum near the air handler

3. in the return air plenum with a deep pleat cartridge

4. angled across the return air plenum to increase cross-sectional area

5. situated in a wall return grille

Figure 4-31: Filter Location Options

Source: California Energy Commission

The MERV 6 pleated filter provides enhanced particulate arrestance, but also provides longer service life than the conventional low efficiency panel filter. Typically, the pleated type filter will last three months or longer, depending upon operating conditions, as compared to the typical one month life cycle of disposable fiberglass filters. The deeper pleated versions will typically provide even longer life cycles, up to a year or more.

4.6.6.9     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.

There are three exceptions to the separation requirements.

1.    Windows or ventilation openings in the wall can be as close as 3 feet to sources of contamination that exit through the roof or to dryer exhausts.

2.    There is no minimum distance between windows and the outlet of a local exhaust outlet from kitchens or bathrooms.

3.    Vent terminations that meet the requirements of the National Fuel Gas Code, which has separation and location requirements, do not need to meet the requirements.

4.6.7                                                                                                                   Air Moving Equipment (Section 7 of ASHRAE 62.2)    

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

4.6.7.1     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 certified (HVI) 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 webpage:

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.

4.6.7.2     Sound Ratings for Fans

One common reason for not using ventilation equipment, particularly local exhaust fans, is the noise they 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 ft 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.

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 whole-building ventilation fans, and also to continuous local ventilation exhaust fans.

B.   Intermittent Fans

Intermittently operated whole-building ventilation fans shall be rated at a maximum of 1.0 sone.  Intermittently operated local exhaust fans shall be rated at a maximum of 3.0 sone, unless the maximum rated airflow is greater than 400 cfm.

Thus, ASHRAE Standard 62.2 extends the requirement for quiet fans to include range hoods and regular bath fans, not just whole-building ventilation system fans. The whole-building fan or other combined systems that operate continuously to provide whole-building ventilation must be rated at 1.0 sone or less, but intermittent local ventilation exhaust fans, including intermittently operated bath fans, must be rated at a maximum of 3.0 sones. Range hoods must also be rated at 3.0 sones or less, but this is at their required “working speed” of 100 cfm. Most range hoods have maximum speeds of much more than 100 cfm, but 100 cfm is the minimum airflow that is required by the Standards.

4.6.7.3     Airflow Rating

All ventilation systems used to meet the whole-building airflow requirement must demonstrate compliance by direct measurement using a flow hood, flow grid, or other measuring device. HERS verification of whole-building airflow is required for newly constructed buildings and additions greater than 1,000 square feet to existing buildings.

Compliance with the ventilation airflow requirements for local exhaust ventilation systems can be demonstrated in one of two ways:

The ventilation system can be tested using an airflow measuring device after completion of the installation to confirm that the delivered ventilation airflow meets the requirement.

Simple exhaust systems can comply by conformance to a prescriptive requirement that the fan has a certified airflow rating that meets or exceeds the required ventilation airflow, and the ducts for the ventilation system 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 inch w.c. operating point. The certified airflow rating of a ventilation device is generally available from the manufacturer, and is available for hundreds of products in the Home Ventilating Institute (HVI) Certified Products Directory at the HVI website (www.hvi.org). Manufacturers can choose whether to provide the certified data for posting at the HVI website, but all of them should have available the rated data at 0.25 inches of water column static pressure.

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 in inspection of the installation(s).

The prescriptive duct design criteria given in Table 4-16 provide maximum duct lengths based on various duct diameters and duct type. As can be seen, the higher the flow, the larger in diameter or shorter in length the duct has to be. Moreover, smooth duct can be used to manage longer duct runs. Interpolation and extrapolation of Table 4-16 (Table 5.3 of ASHRAE 62.2) are not allowed. For airflow values 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 of water column) static pressure

Table 4-16 –: Prescriptive Duct Sizing for Single-Fan Exhaust Systems

ASHRAE 62.2, Table 5.3

4.6.7.4     Multibranch Exhaust Ducting

ASHRAE Standard 62.2 contains restrictions on several 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 from several units in a multifamily building. This section does not preclude the use of that type of system, but it does require that either the shared exhaust fan operate continuously or that 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.

4.6.8                                                                                                                   Multifamily Buildings (Section 8 of ASHRAE 62.2)

Individual dwelling units in multifamily buildings are each required to meet all the IAQ and whole-building ventilation requirements for ASHRAE 62.2 discussed in the preceding section, as modified by this section. This means that the terms “building” and “dwelling” in the preceding sections are referring to single dwelling units for multifamily buildings.

4.6.8.1  Whole-Building Mechanical Ventilation

The methods for determining the required whole-building ventilation rate for multifamily buildings are almost the same as those used for single-family buildings.

As this section will discuss only the differences, it would be beneficial for the reader to review Section 4.6.3 before continuing.

Multifamily buildings must use the fan ventilation rate method to determine the required ventilation rate, specified in this section. The total ventilation rate method cannot be used for multifamily buildings.

The fan system may use an intermittent ventilation option using the same method as Section 4.6.3.2 to determine the required minimum intermittent ventilation flow rate, replacing the use of Equation 4-1and Table 4-14 in Section 4.6.3.2 with Equation 4-9 and Table 4-17.

The continuous whole-building ventilation rate is larger for multifamily buildings, but is given by an equation similar to Equation 4-1 and is calculated in the same manner:

Equation 4-9

Where:

2)

The required ventilation rate may also be found using Table 4-17. This table allows users to find the required ventilation rate directly if they know the floor area and number of bedrooms.

Table 4-17: Dwelling Unit Ventilation Air Requirements, cfm

From ASHRAE 62.2, Table 8.2.1a

Corridors and other common areas within conditioned space must be provided a ventilation rate of 0.06 cfm per ft² of floor area. This required ventilation rate for common areas can be calculated using Equation 4-10:

Equation 4-10

Where:

2)

Nonresidential spaces in mixed-use buildings must meet the requirements of ASHRAE 62.1, Ventilation for Acceptable Indoor Air Quality.

Common parking garages adjoining occupiable spaces, except parking garages with at least two walls that are at least 5 percent open to the outside, must be provided with exhaust ventilation at a rate given by Equation 4-11:

Equation 4-11

Where:

2)

This ventilation rate is much higher per ft² of floor area than most ventilation requirements due to vehicle emission concerns.

4.6.8.2    Other Requirements

ASHRAE Standard 62.2 requires that measures be taken to minimize air movement across envelope components separating dwelling units from adjacent dwelling units and nearby spaces outside the occupiable space of the dwelling unit. This should include sealing all penetrations in envelope components (for example, light fixtures in roofs, outlets in walls, and base boards around the edge of floors) and sealing vertical chases adjacent to units. Pipe and electrical penetrations are also examples of envelope component penetrations that require sealing. The measures must apply to adjacent units both above and below, as well as side by side.

All doors between dwelling units and common areas must be gasketed or made substantially airtight.

The Energy Standards do not require HERS verification of multifamily envelope leakage rates. The builder or installer must implement measures that meet the ASHRAE 62.2 Section 8.4.1 transfer air requirements. The enforcement agency is responsible for determining compliance, thus may specify inspection criteria or other methods such as the diagnostic method detailed in ASHRAE 62.2 Section 8.4.1.1.

4.6.8.3  Air-Moving Equipment

Exhaust fans in separate dwelling units cannot share a common exhaust duct. Exhaust inlets from more than one dwelling unit may be served by a single exhaust fan downstream of all the exhaust inlets if the fan is designed and intended to run continuously or if each inlet is equipped with a backdraft damper to prevent cross-contamination when the fan is not running.

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 and intended to run continuously or if each supply outlet is equipped with a backdraft damper to prevent cross-contamination when the fan is not running.