9.2   ASHRAE Standard 62.2–2016 Ventilation

SWS Details: 6.6201.2 Primary Ventilation Air Flow between Rooms

Most dwellings in North America currently rely on air leakage for ventilation. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) publishes ventila­tion standards for dwellings.

Their current standard, ASHRAE 62.2–2016, defines the roles and minimum requirements for mechanical and natural ventila­tion systems and the building envelope. The roles and require­ments intend to provide acceptable indoor air quality in residential buildings.

9.2.1   ASHRAE 62.2–2016 Components

If you air-seal dwellings during weatherization, you may need to install whole-dwelling mechanical ventilation systems under ASHRAE 62.2–2016, which has 3 components.

1.      Whole-dwelling ventilation.

2.      Local ventilation.

3.      Natural infiltration credit.

This ventilation standard allows for natural infiltration (air leak­age) to contribute toward the required whole-dwelling ventila­tion rate for single-family homes and horizontally attached multifamily buildings (but not vertically attached multifamily buildings.

9.2.2   Whole-Dwelling Ventilation Requirement

SWS Details: 6.9901.1 Supplemental Ventilation Information—ASHRAE 62.2, 6.6204.1 Commissioning Ventilation Systems, 6.6201.2 Primary Ventilation Air Flow between Rooms, 6.6202.1 Controls, 6.6288.1 Sound-Rating Limits

To comply with ASHRAE 62.2–2016, use either the formula or the table shown here to determine the whole-dwelling ventila­tion airflow requirement.

You can provide this mechanical airflow in 4 ways.

1.      A dedicated exhaust or supply fan running continuously or cycling by automatic control.

2.      A bathroom or kitchen exhaust fan running continu­ously or cycling by automatic control.

3.      A central air handler drawing filtered outdoor air into its return.

4.      A balanced ventilation system such as a heat-recovery ventilator (HRV) or energy-recovery-ventilator (ERV).

Room Pressure Imbalances

If any room in the building exceeds ±3 pascals pressure with ref­erence to the common area when all interior doors are closed and while the ventilation system is operating, take action to reduce the pressure. Install transfer grilles or jumper ducts as needed to reduce the room to common area pressure difference to less than ±3 pascals. SWS Detail: 6.6201.2 Primary Ventilation Air Flow between Rooms

Option 1: Finding the Airflow Requirement Using the Formula

If you want to install the minimum ventilation capacity, use these 3 steps to follow the formula option.

1.      Determine the floor area of the conditioned space of the home in square feet (Afloor).

2.      Determine the number of bedrooms (Nbr).

3.      Insert these numbers in the formula shown next.

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Option 2: Finding the Airflow Requirement Using the Table

Note: If you know the number of occupants, compare the number of occupants with the number of bedrooms plus 1 and use the higher of those two values.

You can also determine the required continuous fan airflow under ASHRAE 62.2–2016 using the table shown here.

Table 9-1:         Continuous CFM Fan Airflow Requirements

Floor Area (ft2)

Number of Bedrooms

1

2-

3

4

5

Less Than 500

30

38

45

53

60

501-1000

45

53

60

68

75

1001-1500

60

68

75

83

90

1501-2000

75

83

90

98

105

2001-2500

90

98

105

113

120

2501-3000

105

113

120

128

135

3001-3500

120

128

135

143

150

3501-4000

135

143

150

158

165

4001-4500

150

158

165

173

180

4501-5000

165

173

180

188

195

From ASHRAE Standard 62.2-2016

Additional Ventilation Guidance

If the ventilation airflow requirement is less than 15 CFM, ASHRAE 62.2–2016 exempts the mechanical-ventilation requirement.

Residential Energy Dynamics provides a free online tool to help calculate ASHRAE 62.2–2016 ventilation rates.

Refer to the ASHRAE standard for more details, guidance, and exceptions that are beyond the scope of this field guide.

9.2.3   Local Exhaust Ventilation Requirement

SWS Detail: 6.6002.3 Exhaust-Only Ventilation—Fan Intake Grille Location, 6.6003.3 Through the Wall, 6.6005.2 Kitchen Range

There are two options for complying with the local ventilation requirements for kitchens and bathroom: demand-controlled exhaust or continuous exhaust.

1.      For demand-controlled exhaust specify a minimum of 100 CFM for the kitchen, and 50 CFM for each bath­room. An operable window reduces a bathroom’s venti­lation requirement to 30 CFM.

2.      For continuous exhaust specify a minimum of 20 CFM for each bathroom, and 5 ACH for the kitchen (based on volume).

Local Exhaust Deficit

If the existing kitchen or bathroom ventilation doesn’t meet the requirements stated here, you may adjust the whole-dwelling ventilation rate to compensate for the local airflow deficits. Fol­low these steps to calculate the local-ventilation deficit in CFM that must be added to the whole-dwelling ventilation rate.

1.      Determine the total local exhaust ventilation require­ment for all kitchens and bathrooms.

2.      Measure the delivered airflow of existing kitchen or bathroom exhaust fans using flow hood, flow grid, or other airflow measuring device. Subtract this amount from the total local exhaust ventilation requirement.

3.      If the local jurisdiction allows for operable windows to provide for local ventilation, subtract 20 CFM for each kitchen or bathroom that has an operable window.

The result of these steps is the local exhaust ventilation deficit in CFM. Add 1/4 of this deficit to the required whole-dwelling ven­tilation rate.

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9.2.4   Infiltration Credit

ASHRAE 62.2–2016 allows for infiltration to contribute to the dwelling’s ventilation airflow. Infiltration can supply the entire whole-dwelling ventilation requirement for very leaky build­ings. For moderately leaky buildings, infiltration may supply some of the building’s ventilation.

Both single-family and multifamily buildings that are hori­zontally attached (low rise) are eligible for the infiltration credit.

You can determine the amount of the infiltration credit with a blower door test and weather data based on the building’s loca­tion. Calculating the infiltration credit without software is com­plicated. To simplify the calculations, use the RED Calc Free online tool and select “yes” for the “Use the infiltration credit” option.