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Whole-House Mechanical Ventilation System meets ASHRAE 62.2

The U.S. Department of Energy (DOE) Zero Energy Ready Home National Program Requirements specify that homes can follow either a prescriptive or performance path to be certified. Homes following the prescriptive path must meet all of the requirements listed in the Program Requirements Exhibit 1 and 2. Homes following the performance path must match the level of performance of a target home constructed to meet all of the mandatory requirements listed in the National Program Requirements Exhibit 1 and all of the requirements listed in Exhibit 2. Exhibit 2 includes ventilation requirements, which are excerpted in Table 1.

Table 1 shows the minimum exhaust fan efficacy requirements in cubic feet per minute per Watt for ASHRAE 62.2-compliant ventilation in the hot, mixed, and cold climates.

Table 1. Excerpt from Exhibit 2: DOE Zero Energy Ready Home Target Home Showing the Ventilation Fan Efficacy Requirements

The whole-house mechanical ventilation system can be designed to meet the ventilation requirements in one of several ways (DOE 2012): supply-only ventilation, exhaust-only ventilation, balanced ventilation with a heat recovery ventilator (HRV) or energy recovery ventilator (ERV), or intermittently balanced using a combination of timered exhaust fans and supply ventilation using fresh air intake ducts that are attached to the central air handler or equipped with their own fan.
For more information about whole-house ventilation options, see the guide Whole-Building Delivered Ventilation, which describes exhaust, supply, and balanced ventilation strategies.

How to Determine Fan Efficacy

The efficacy of the fans included in the whole-house ventilation system must be verified. Verifying the fan efficacy depends on the information available. The cfm/W may be listed on the specification sheet for the fan. If multiple values are listed, choose the airflow (cfm) shown on the mechanical plans and 0.1 in. of static pressure (in. w.c.). If efficacy is not listed, it can be calculated from published watts and specified airflow (cfm). For example, a fan with an airflow of 80 cfm at 0.100 in. w.c. and a wattage of 48 W has an efficacy of (80÷48=) 1.67 cfm/W.  If the wattage is not specified, it can be calculated from the fan voltage and amperage. (To calculate watts, multiply volts times amps times an assumed power factor for the fan motor (for example 0.75PF). Also see Continuous Supply/Exhaust Fan Ratings.

Climate zones are based on the Climate Zone Map found in the 2012 International Energy Conservation Code (2012 IECC Figure C301.1):

IECC climate zone map
Figure 1. IECC climate zone map


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References and Resources*

  1. Author(s): ASHRAE
    Organization(s): ASHRAE
    Publication Date: January, 2013

    Standard defining the roles of and minimum requirements for mechanical and natural ventilation systems and the building envelope intended to provide acceptable indoor air quality in low-rise residential buildings.

  2. Author(s): Department of Energy
    Organization(s): DOE
    Publication Date: August, 2012

    IECC code note explaining new fan efficacy requirements, along with how to determine which fans are affected by the new fan requirements.

  3. Author(s): Maxwell, Berger, Zuluaga
    Organization(s): CARB, Steven Winter Associates, SWA
    Publication Date: July, 2014

    Report outlining research that helps inform best practices for air sealing multi-family buildings in the Northeast.

Last Updated: Friday, August 1, 2014