Air infiltration can be a significant component of thermal losses in residential buildings. In the Home Energy Saver, we calculate the energy impact of air infiltration in the DOE-2 simulation model, based on the leakage area of the thermal shell and location-specific weather data. Although leakage area can be measured using diagnostic testing such as with a blower door, few homeowners know the leakage area of their home, so we provide two options: 1) A simplified estimate based on building characteristics and 2) Direct entry of the measured leakage at 50 pascals (CFM50).

1. Estimate of Building Characteristics

For this method we estimate leakage area using a regression model based on analysis of a database of measured leakage values compiled by the Residential Buildings Systems group at LBNL, Chan, Joh and Sherman, 2013 (see also:  Among the key variables in the model are the year built, climate zone in which the house is located, the floor area, building height, whether the home was included in a weatherization assistance program or was rated for energy efficiency, foundation type and whether the ducts are located in conditioned or unconditioned space.

The calculation of fractional leakage area is as follows:

(1) First Normalized Leakage (NL) is calculated -


    Floor Area           = conditioned floor area in meters2

    Cfloor area                =coefficient for conditioned floor area (see table 1)

    Building Height   = height of the building in meters  

    CHeight                    = coefficient for the building height(see table 1)

    Sealed                = whether the home has been professionally air sealed (Y/N)

    Csealed                = coefficient for building is sealed (see table 1)

    Cvintage               = coefficient for the vintage bin (see table 1)          

    CIECC                  = coefficient for the International Energy Conservation Code (IECC) climate zone bin (see table 1) 

    Cfoundation          = coefficient for the foundation type (see table 1)

    Cduct                       = coefficient for the duct location (see table 1)

    Stories               = number of floors above grade

(2) Fractional leakage Area (FLA) is derived from Normalized Leakage -

           FLA = Normalized Leakage / 1000 * Stories ^ 0.3

Table 1. Coefficients for the infiltration regression model

2. Direct Entry of Measured Leakage

Building shell leakage is typically measured using a blower door that pressurizes the living space to 50 pascals. This measurement is converted to fractional leakage area using the following equations:

    Q50si = Q50ip x 0.0004719474 ft3/min / m3/sec

    Q4 = Q50si x (4 / 50) 0.65

    ELA = Q4 / (((2 / 1.2) x 4)0.5)

    FLA = (ELA / (0.09290304 m2 / ft2)) / A


    Q50 - Air flow measured at 50 pascals (ft3/min for ip and m3/sec for si)

    Q4   - Air flow at 4 pascals

    ELA  - Effective  leakage area (in m2)

    FLA  - Fractional leakage area

    A     - Floor Area (ft2)