Air Leakage and Air 

Transfer Between Garage 

and Living Space

Armin Rudd

Building Science Corporation

September 2014
NOTICE

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Air Leakage and Air Transfer Between Garage and Living Space

Prepared for: 

The National Renewable Energy Laboratory 

On behalf of the U.S. Department of Energy’s Building America Program 

Office of Energy Efficiency and Renewable Energy 

15013 Denver West Parkway 

Golden, CO 80401 

NREL Contract No. DE-AC36-08GO28308 

Prepared by: 

Armin Rudd 

3 Lan Drive, Suite 102 

Westford, MA 01886 

NREL Technical Monitor: Stacey Rothgeb 

Prepared under Subcontract No. KNDJ-0-40337-04 

September 2014 
The work presented in this report does not represent 

performance of any product relative to regulated 

minimum efficiency requirements.

The laboratory and/or field sites used for this work are 

not certified rating test facilities. The conditions and 

methods under which products were characterized for 

this work differ from standard rating conditions, as 

described.

Because the methods and conditions differ, the reported 

results are not comparable to rated product performance 

and should only be used to estimate performance under 

the measured conditions.
iii

Contents

List of Figures ............................................................................................................................................ iv

List of Tables ............................................................................................................................................... v

Definitions................................................................................................................................................... vi

Acknowledgments .................................................................................................................................... vii

Executive Summary................................................................................................................................. viii

1 Problem Statement............................................................................................................................... 1

1.1 Introduction and Background .......................................................................................................... 1

1.2 Review of Prior Publications........................................................................................................... 1

1.3 Research Questions.......................................................................................................................... 2

1.4 Relevance to Building America’s Goals.......................................................................................... 2

1.5 Tradeoffs and Other Benefits........................................................................................................... 3

1.6 Technical Approach......................................................................................................................... 3

2 Results................................................................................................................................................. 12

2.1 Fan Pressurization Testing............................................................................................................. 12

2.2 Tracer Gas Testing......................................................................................................................... 19

2.2.1 SF6 Test 1: Initial Baseline ............................................................................................... 23

2.2.2 SF6 Test 2: 165 cfm House Exhaust ................................................................................. 24

2.2.3 SF6 Test 3: 165 cfm House Supply ................................................................................... 26

2.2.4 SF6 Test 4: 165 cfm House Exhaust and 70 cfm Garage Exhaust .................................... 27

2.2.5 SF6 Test 5: 330 cfm House Exhaust ................................................................................. 28

2.2.6 SF6 Test 6: Final Baseline................................................................................................. 29

3 Conclusions ........................................................................................................................................ 32

References and Bibliography .................................................................................................................. 26
iv

List of Figures

Figure 1. Top left: front view of the test house; top right: rear view; bottom left: front-right view; 

bottom-right: front left view................................................................................................................. 3

Figure 2. First floor plan, with garage-to-house interface walls marked with thick red lines, and 

with red dots marking measurement station locations.................................................................... 4

Figure 3. Second floor plan, with garage attic-to-house interface walls marked with thick red lines, 

and with red dots indicating measurement station locations ......................................................... 5

Figure 4. Location of the house-to-outdoors fan pressurization testing equipment........................... 6

Figure 5. Location of garage-to-house fan pressurization testing equipment..................................... 7

Figure 6. Six channels of pressure monitoring, using Energy Conservatory digital pressure gauge 

having auto ranging resolution of 0.1 Pa and accuracy of ±1% of reading or 2 times the 

resolution, whichever is greater ......................................................................................................... 7

Figure 7. First floor garage-to-house wall cavity pressure measurement location, and second floor 

garage attic-to-house wall cavity pressure measurment and room air sampling location .......... 8

Figure 8. Back side of house-to-garage attic wall ................................................................................... 8

Figure 9. Testing equipment located in the garage: SF6 tracer gas on a scale and mass flow 

controller for tracer gas injection (lower left); calibrated fan for garage exhaust (upper left); 

garage air concentration and temperature/RH sampling station (tripod in center); mixing fan 

(right); garage air pressure sampling tube (far right)....................................................................... 9

Figure 10. Six channels of tracer gas concentration monitoring, using a Bruel & Kjaer 1302 

photoacoustic gas analyzer with internal temperature and water-vapor compensation, SF6

detection limit of 5 ppb, and a repeatability specification of 1% of measured value.................... 9

Figure 12. Test results showing inadequacy of house-to-garage pressure differential as a single 

criterion for house-to-garage airtightness....................................................................................... 18

Figure 13. Elimination of false positives was found by adding a second criterion limiting the 

increase in house CFM50 to 6% with the overhead garage door open compared to closed ..... 18

Figure 14. House leakage area increased by less than half the physical house-to-garage opening 

area added........................................................................................................................................... 19

Figure 15. Weather conditions during the six tracer gas testing periods........................................... 21

Figure 16. Indoor temperature and humidity conditions during the six tracer gas tests.................. 22

Figure 17. SF6 test 1, initial baseline tracer gas test showing that, by the end of the 24 hour test, 

about 1.4% of the air in the house came from the garage (0.3/22 = 0.014)................................... 24

Figure 18. SF6 Test 1, Baseline, monitored pressure differentials showing the garage pressure 

about 0.5 Pa positive with respect to the house ............................................................................. 24

Figure 19. SF6 test 2, 165 cfm house exhaust ventilation tracer gas test showing that, by the end of 

the 24 hour test, 4.6% ±1.4% of the air in the house came from the garage (0.78/17 = 0.046) ... 25

Figure 20. SF6 Test 2, 165 cfm House Exhaust, monitored pressure differentials showing the 

garage pressure about 2 Pa positive with respect to the house................................................... 25

Figure 21. SF6 Test 3, 165 cfm House Supply ventilation tracer gas test showing that, by the end of 

the 24 hour test, supply ventilation had suppressed essentially all air transfer from the garage 

to the house (0.1/20 = 0.005).............................................................................................................. 26

Figure 22. SF6 test 3, 165 cfm house supply, monitored pressure differentials showing the garage 

pressure about 1.5 Pa negative wrt the house................................................................................ 26

Figure 23. SF6 test 4, 165 cfm house exhaust and 70 cfm garage exhaust tracer gas test showed 

performance that was about the same as for the initial baseline test (0.1/5.0 = 0.02) ................ 27

Figure 24. SF6 test 4, 165 cfm house exhaust and 70 cfm garage exhaust, monitored pressure 

differentials showing the garage pressure about 2 Pa negative wrt the house .......................... 27

Figure 27. SF6 Test 6, the final Baseline tracer gas test showed again that there was little garageto-house air transfer across the well-sealed garage to house interface (0.16/25=0.006) ........... 29

Figure 29. Pressure differential of the garage wrt house for each tracer gas test............................. 30

Figure 30. Ratio of average house SF6 concentration to garage SF6 concentration for the last 4 

hours of each test, representing the fraction of house air that came from the garage .............. 31

Unless otherwise noted, all figures were created by the BSC team.
v

List of Tables

Table 1. SF6 Injection Rate Needed ........................................................................................................ 11

Table 2. Listing of Pressure Differential Monitoring Channels ............................................................ 12

Table 3. Detailed Description of Each House and Garage Pressurization Test ................................. 13

Table 4. Results of House and Garage Fan Pressurization Tests ....................................................... 14

Table 5. Comparison of Test Results Between Guarded Blower Door Test and ZPD Test............... 16

Unless otherwise noted, all tables were created by the BSC team.
vi

Definitions

ACH Air Changes per Hour

ACH50 Air Changes per Hour at 50 Pascal Pressure Differential

ASHRAE American Society of Heating, Refrigerating and Air-Conditioning 

Engineers

BSC Building Science Corporation

CFM50 Cubic Feet per Minute at 50 Pascal Test Pressure Differential

DOE U.S. Department of Energy

ELA Effective Leakage Area

EPA U.S. Environmental Protection Agency

IECC International Energy Conservation Code 

IRC International Residential Code

Pa Pascal; SI Unit of Pressure

RH Relative Humidity

SF6 sulfur hexafluoride

wrt With Respect To

ZPD Zone Pressure Diagnostics
vii

Acknowledgments

This project was supported by the U.S. Department of Energy (DOE), Office of Building 

Technologies, Building America Program. The author appreciates K. Hovnanian Homes –

Landover Group who provided the house for testing over a 1-week period, Cheryn Metzger and 

Michael Gestwick of the National Renewable Energy Laboratory for technical management and 

field testing equipment support, Ed Hancock of Mountain Energy Partnership for field testing 

support, Bob Axelrad of the U.S. Environmental Protection Agency (EPA) for collaboration 

relative to EPA’s Indoor airPLUS requirements, and Eric Martin of Florida Solar Energy Center 

for loaning some test equipment.
viii

Executive Summary

This research project focused on evaluation of air transfer between the garage and living space in 

a single-family detached home constructed by a production homebuilder in compliance with the 

2009 International Residential Code and the 2009 International Energy Conservation Code. The 

project gathered important information about the performance of whole-building ventilation 

systems and garage ventilation systems as they relate to minimizing flow of contaminated air 

from garage to living space. Important gaps and barriers addressed by this research were:

• Developing recommendations for effective methods for precluding the flow of 

contaminated air from garages to living space.

• Creating a resource for guiding home builders and retrofitters to achieve garage isolation 

by use of mechanical ventilation equipment.

• Providing field measurement support for revision of the EPA Indoor airPLUS program 

requirements, which are part of the DOE Challenge Home program.

A series of 25 multipoint fan pressurization tests and additional zone pressure diagnostic testing 

characterized the garage and house air leakage, the garage-to-house air leakage, and garage and 

house pressure relationships to each other and to outdoors using automated fan pressurization 

and pressure monitoring techniques.

Measured house-to-garage air leakage, using multi-point computer automation, was 89 cfm at a 

50 Pa pressure differential (89 CFM50). The resulting garage-to-house effective leakage area 

was 12.4 in.

2

. These values fell between the minimum and maximum values predicted by a 

separate computerized zone pressure diagnostic test.

With the house at –50 Pa with respect to (wrt) outdoors, and no imposed house-to-garage or 

garage-to-outside leakage, the garage-to-house pressure differential was –47 Pa. With 25 in2

house-to-garage leakage imposed, the garage-to-house pressure dropped to –28 Pa, then with 100 

in.

2 garage-to-outside leakage imposed, the garage-to-house pressure raised back up to –46 Pa.

This example showed that a relatively leaky house-to-garage interface can fail or pass a single 

garage-to-house pressure differential test criterion depending on the actual garage-to-outside 

leakiness.

The extensive testing to evaluate the adequacy of the draft EPA Indoor airPLUS pressure 

differential criterion showed that using a CFM50 differential criterion in combination with the 

pressure differential criterion would eliminate false positives. In the original first step of the test, 

while a house-to-outside CFM50 test is being conducted with all operable garage openings 

closed, a garage-to-house pressure measurement is taken. The garage-to-house pressure 

differential must be greater than 45 Pa. A new second step would require an additional 

measurement of house-to-outside CFM50 with the overhead garage door open, and verifying that 

the CFM50 with the garage door open is not more than 6% greater than the CFM50 with the 

garage door closed. The second step eliminates false positives that can result in the first step due 

to certain combinations of house-to-garage and garage-to-outside series leakage.
ix

For this test house, the garage-to-house pressure differential was 47 Pa with the house at –50 Pa 

wrt outdoors and all operable garage openings closed, and the house CFM50 air leakage did not 

increase when tested with the overhead garage door open. 

Six tracer gas tests conducted to determine the fraction of house air that came from the garage 

under different operating conditions yielded the following conclusions:

• The operation of different ventilation systems showed a consistent and steady difference 

in the fraction of house air that came from the garage. From high to low fraction, the 

order was: House Exhaust, Baseline, House Exhaust+Garage Exhaust, and Supply.

• The initial Baseline test showed that 1.4% ±1.4% of the air in the house came from the 

garage. The house pressure was about 0.5 Pa negative wrt the garage. The final Baseline 

test showed that 0.6% ±1.4% of the air in the house came from the garage. Averaging 

both Baseline tests revealed that about 1% ±1.4% of the air in the house came from the 

garage when no mechanical ventilation system was operating, or close to five times less 

than when operating 165 cfm of House Exhaust ventilation.

• The 165 cfm House Exhaust ventilation test showed that about 4.6% ±1.4% of the air in 

the house came from the garage. The house pressure was about 2 Pa negative wrt the 

garage.

• The 165 cfm House Supply ventilation test showed that the supply ventilation suppressed 

essentially all air transfer from the garage to the house. The house pressure maintained 

about 1.5 Pa positive wrt the garage.

• The 165 cfm House Exhaust plus 70 cfm Garage Exhaust test showed performance that 

was about the same as the initial Baseline test; however, it is possible that some tracer gas 

being exhausted to outdoors from the garage may have come into the house because of 

house depressurization due to the house exhaust ventilation. Garage Exhaust of 70 cfm 

was sufficient to depressurize the garage 2 Pa wrt the house and thereby preclude garageto-house air transfer.

While the relative characteristics of this house may not represent the entire population of new 

construction configurations and airtightness levels (house and garage) throughout the country, 

the technical approach was conservative and should reasonably extend the usefulness of the 

results to a large spectrum of house configurations from this set of parametric tests in this one 

house. Based on the results of this testing, the two-step garage-to-house air leakage test protocol 

described above is recommended where whole-house exhaust ventilation is employed. For 

houses employing whole-house supply ventilation (positive pressure) or balanced ventilation 

(same pressure effect as the Baseline condition), adherence to the EPA Indoor airPLUS house-togarage air sealing requirements should be sufficient to expect little to no garage-to-house air 

transfer.
1

1 Problem Statement

1.1 Introduction and Background

Indoor air contaminant control within a home begins with source control; that is, avoiding the 

placement of items of known high contaminant emission inside the living environment.

Occupant-controlled local exhaust is used inside the home in areas where high emissions from 

contaminant sources cannot be avoided, such as kitchens, bathrooms (wet rooms), toilet rooms, 

and possibly laundry rooms. Finally, whole-building controlled mechanical ventilation is used to 

dilute remaining, more diffuse indoor contaminants with fresher outside air (Rudd 2011(b)).

This project focused on the source of outside air as it pertains to “ventilation” air that may come 

from polluted air in the garage. Garage air can enter the living space especially when the living 

space is at a negative pressure with respect to (wrt) the garage due to natural forces or due to use 

of mechanical exhaust ventilation in the living space. This project builds on previous work 

(Rudd and Bergey 2014; Rudd 2014a, 2014b) to further examine and evaluate the problem of 

unwanted air transfer from garage to living space and the effectiveness of Garage Exhaust 

ventilation or House Supply ventilation to provide a solution to that. The effectiveness of Garage 

Exhaust requirements in the U.S. Environmental Protection Agency (EPA) Indoor airPLUS 

Construction Specifications1 were examined in order to consider the most effective methods of 

meeting the U.S. Department of Energy (DOE) Challenge Home criteria, which require meeting 

the EPA Indoor airPLUS criteria. This project did not address issues related to air handlers or 

heating, ventilation, and air conditioning system ductwork located in garages, since the EPA 

Indoor airPLUS requirements, and therefore the DOE Challenge Home, preclude that. 

This research project supports developing the metrics for adapting existing ventilation system 

configurations and controls to enhance ventilation effectiveness regarding how garages relate to 

living spaces, while reducing capital costs and saving energy overall. The output from this work 

will be the input into both retrofit and new house construction best practices and can be used to 

update the Ventilation Measure Guideline (Rudd 2011(a) previously produced by Building 

Science Corporation (BSC).

1.2 Review of Prior Publications

Some studies have shown that house infiltration through attached garages can be problematic. 

Emmerich et al. (2003) reported that polluted garage air infiltrated into living quarters, and that 

being as much as 45% of total house infiltration according to Fugler et al. (2002).

Graham et al. (1999) used sulfur hexafluoride (SF6) tracer gas to test multiple Canadian houses 

and found that concentration peaks in the living area ranged from negligible to about 15% of the 

garage concentration. Similar results were found by cold starting a car engine and measuring 

 1 Version 1, Revision 1 of the EPA Indoor airPLUS Construction Specifications required: “Attached garages shall be 

isolated from conditioned spaces as follows: Common walls and ceilings between attached garages and living spaces 

shall be visually inspected to ensure they are air-sealed before insulation is installed. All connecting doors between 

living spaces and attached garages shall include an automatic closer, and they shall be installed with gasket material 

or be made substantially air-tight with weather stripping. 5.6 Attached garages shall include an exhaust fan, with a 

minimum installed capacity of 70 cfm, rated for continuous operation, and installed to vent directly outdoors. If 

automatic fan controls are installed, they shall activate the fan whenever the garage is occupied and for at least 1 

hour after the garage has been vacated.”
2

carbon monoxide concentrations. Other studies found transport of carbon monoxide and other 

automobile engine exhaust compounds between attached garages and house living space to be 

common as well (Wilber and Klossner 1997; Tsai and Weisel 2000). Kaluza (1999) reported that 

keeping the garage at a negative pressure relative to the house prevented carbon monoxide

transport into a house in Alaska. A combination of air sealing and garage exhaust was reported to 

be an effective strategy by Wilber and Klossner (1997). Fugler et al. (2002), Greiner and Schwab 

(1998), and Furtaw et al. (1993) all recommended garage exhaust to improve house and garage 

air quality.

1.3 Research Questions

The research presented in this report was intended to help develop a better understanding of air 

transfer between garages and living spaces in single-family homes. The following research 

questions pertain to this project relative to a home constructed by a BSC builder partner:

1. What is the measured effective leakage area (ELA) of the garage-to-house interface?

2. What is the garage-to-house pressure relationship for a range of house-to-outside pressure 

differentials and for a range of imposed leakage areas between: a) the garage and house, 

and; b) between the garage and outside? (The purpose of imposing leakage was to 

investigate potential improvements to the EPA Indoor airPLUS requirements.)

3. Is there a simple test criterion that could define an adequately sealed garage-to-house 

interface?

4. What is the fraction of house living space air that comes from the garage, and what is the 

house-to-garage pressure relationship, under operation of different whole-house 

ventilation systems, and with operation of the 70 cfm EPA Indoor airPLUS compliant 

Garage Exhaust?

1.4 Relevance to Building America’s Goals

Overall, the goal of the DOE Building America program is to “reduce home energy use by 30%-

50% (compared to 2009 energy codes for new homes and pre-retrofit energy use for existing 

homes).” To this end, we conduct research to “develop market-ready energy solutions that 

improve efficiency of new and existing homes in each U.S. climate zone, while increasing 

comfort, safety, and durability.”2

Physical isolation through good air sealing techniques is an important first step, but that may be 

impractical in retrofit situations and may be imperfect in new construction. The purpose of this 

project is to evaluate mechanical methods to preclude flow of contaminated air from garages to 

living space in a home where whole-building ventilation is operating. Good indoor air quality is 

a goal of the Building America Program and attached garage isolation from living space is an 

important aspect of ensuring good indoor air quality. Certain types of whole-building mechanical 

ventilation may contribute more than others to that goal. Situations where natural driving forces 

or whole-building mechanical ventilation may cause contaminated air to flow from a garage to 

the house should be avoided. Currently, the ENERGY STAR® Indoor airPLUS requirement of 

Garage Exhaust is required for compliance with the DOE Challenge Home Program. The infield 

performance of that requirement needs to be tested. This presents an opportunity for considering 

 2 http://www1.eere.energy.gov/buildings/building_america/program_goals.html
3

the most effective methods of meeting the DOE Challenge Home criteria, which require meeting 

the EPA Indoor airPLUS criteria.

1.5 Tradeoffs and Other Benefits

Using mechanical means to control the pressure relationship between an attached garage and the 

living space can preclude flow of contaminated air from the garage to the house. Where wholebuilding mechanical exhaust ventilation is used in the living space, adding mechanical exhaust in 

the garage may improve indoor air quality for the occupants; however, using whole-building 

supply ventilation in the living space to reverse the garage-to-house pressure relationship may 

also solve the problem. Note that in cold climates homes with elevated wintertime indoor 

humidity, exterior insulated sheathing or extensive building enclosure air sealing must ensure 

against potential sheathing condensation when using supply (positive pressure) ventilation. 

1.6 Technical Approach

The project tested a 4,252-ft2 conditioned floor area, two-story, with full unfinished basement 

house in Maryland, southeast of Washington D.C. The home was constructed to comply with the 

2009 International Residential Code (IRC) and the 2009 International Energy Conservation Code 

(IECC) by builder partner K. Hovnanian Homes. The construction specifications specifically 

listed: “Exterior walls and penetrations will be sealed per section 402.41 of the 2009 IECC with 

caulk, gaskets, weatherstripping, or an air barrier of suitable material.” The builder did not seek 

ENERGY STAR certification.

Figure 1. Top left: front view of the test house; top right: rear view;

bottom left: front-right view; bottom-right: front left view
4

A suitable test home was found that had a medium to low level of garage-to-house connection.

One long side of the garage and a little less than half of the short side were adjacent to the first 

story of the house. A second-story bathroom and a walk-in closet were adjacent to the garage 

attic. There was no tuck-under portion where the garage ceiling was adjacent to a conditioned 

space floor above. Figure 2 and Figure 3 show a plan view of this configuration for the first and 

second floors, respectively.

Figure 2. First-floor plan, with garage-to-house interface walls marked with thick red lines, and 

with red dots marking measurement station locations
5

Figure 3. Second-floor plan, with garage attic-to-house interface walls marked with thick red lines, 

and with red dots indicating measurement station locations

The fan pressurization testing portion of this study was better served by a house with a lower 

level of garage-to-house connection because higher levels could be simulated by adding leakage 

area via measured amounts of door opening but obtaining lower levels of leakage would not be 

feasible. As a conservative approach, tracer gas testing results for this house, having a minimum 

garage-to-house surface area ratio would be expected to show a low percentage of house air 

coming from the garage. Smaller houses and those with a higher ratio of garage interface area to 

overall surface area would be expected to behave worse. Therefore, valid tracer gas test results 

from this house should be more valid in smaller houses or houses with a higher garage-to-house 

connection, making these test results appropriate to cover a large spectrum of house 

configurations from a single set of tests in a single house. Tracer gas testing of houses with 

higher levels of garage-to-house connection would be valuable and should be pursued.

Testing was designed to answer the research questions listed above (Section 1.2). The testing 

included measurements of:

• Building enclosure air leakage by fan pressurization

• Six channels of pressure differential monitoring, 5 s average, including:

o House wrt outside
6

o Garage wrt outside

o Basement wrt outside

o First-floor garage wall cavity wrt outside

o Second-floor garage attic wall cavity wrt outside

o Garage wrt house (living space)

• Ventilation fan airflow

• Six channels of sf6 concentration, 2 min sample interval, including:

o Garage

o First-floor main area

o First-floor utility room next to garage wall

o Second-floor main area

o Second-floor bathroom next to garage attic wall

o Basement

• Outdoor wind speed and wind direction

• Indoor and outdoor temperature and relative humidity (RH).

Figure 4. Location of the house-to-outdoors fan pressurization testing equipment
7

Figure 5. Location of garage-to-house fan pressurization testing equipment

Figure 6. Six channels of pressure monitoring, using Energy Conservatory digital pressure gauge 

having auto ranging resolution of 0.1 Pa and accuracy of ±1% of reading or 2 times the resolution, 

whichever is greater
8

Figure 7. First-floor garage-to-house wall cavity pressure measurement location, and second-floor 

garage attic-to-house wall cavity pressure measurment and room air sampling location

Figure 8. Back side of house-to-garage attic wall
9

Figure 9. Testing equipment located in the garage: SF6 tracer gas on a scale and mass flow 

controller for tracer gas injection (lower left); calibrated fan for garage exhaust (upper left); garage 

air concentration and temperature/RH sampling station (tripod in center); mixing fan (right); 

garage air pressure sampling tube (far right)

Figure 10. Six channels of tracer gas concentration monitoring, using a Bruel & Kjaer 1302 

photoacoustic gas analyzer with internal temperature and water-vapor compensation, SF6

detection limit of 5 ppb, and a repeatability specification of 1% of measured value
10

Figure 11. First-floor main air sampling station

A series of 25 multipoint fan pressurization tests and additional zone pressure diagnostic testing 

characterized the garage and house and the garage-to-house leakage areas and pressure 

relationships using automated fan pressurization techniques.

ELA is given in square inches at a pressure differential of 4 Pa as shown in Equation 1.

Eq. 1

where: = airflow at a pressure differential of 4 Pa

Airflow calculated according to a power law curve fit of multiple test points is given in Equation 

2.

Eq. 2

where: = airflow (cfm, ft3/min)

= constant

= pressure differential (Pa)

n = flow exponent

Eq. 3

A series of six tracer gas tests were conducted to determine how air moved from the garage to 

the house living space under baseline conditions and operation of different whole-house 

ventilation systems. SF6 was injected in the garage at a constant mass flow rate. The target SF6

concentration in the garage was a minimum of about 5 ppm with Garage Exhaust operating. As 

shown in Table 1, with a Garage Exhaust flow of 70 cfm, the mass flow controller for injection 

of SF6 was set to 10 SCCM (0.010 L/min). SF6 concentration was measured in the garage and all 

rooms of the living space continuously throughout each test period using a Bruel & Kjaer
11

1302/1303 photoacoustic gas analyzer/sampler system. A Miran model 203B portable gas 

analyzer calibrated for SF6 was also used periodically as a second check of SF6 concentration.

Air mixing in the garage and each living space room was accomplished using oscillating fans to 

ensure uniform concentration in each room. Two inline fans with flexible ductwork were used to 

mix/homogenize air between the first and second floors.

Table 1. SF6 Injection Rate Needed

Airflow 

Rate 

(ft3/min)

SCCM (Standard cm3/min) Needed To Maintain Listed ppm at Listed Airflow Rate

Concentration (ppm)

1 2 3 4 5 6 7 8 9 10

50 1.42 2.83 4.25 5.66 7.08 8.50 9.91 11.33 12.74 14.16

60 1.70 3.40 5.10 6.80 8.50 10.19 11.89 13.59 15.29 16.99

70 1.98 3.96 5.95 7.93 9.91 11.89 13.88 15.86 17.84 19.82

80 2.27 4.53 6.80 9.06 11.33 13.59 15.86 18.12 20.39 22.65

90 2.55 5.10 7.65 10.19 12.74 15.29 17.84 20.39 22.94 25.49

Data analysis included analysis of the fan pressurization testing for characterization of the 

building leakage area between the garage and living space, and analysis of the tracer gas testing 

to measure the transfer of air between the garage and living space under operation of different 

ventilation systems in the living space and the garage.

The fraction of living space air that came from the garage at any point in time was calculated by 

the ratio of SF6 concentration in the living space to the SF6 concentration in the garage, Equation 

4. The tracer gas tests were generally run for 12 hours; however, steady state was not required 

for this analysis approach.

Eq. 4

where: = concentration in the living space (house)

= concentration in the garage

The Bruel & Kjaer 1302 photoacoustic gas analyzer has internal temperature and water-vapor 

compensation, and has a repeatability specification of 1% of measured value. The repeatability 

specification, rather than an absolute accuracy specification, is the relevant specification for error 

analysis in this case since the Eq. 4 calculation is a dimensionless result based on the relative 

concentrations. For example, the error in the quotient 0.3 ppm/22 ppm is ±1.4%, resulting from 

the quotient propagation of error rule which sums the error of each part in quadrature 

[(22*.01)/22)2 + (0.3*.01/0.3)2

]

0.5. Because the repeatability measurement error is given in 

percent of measured value, the Eq. 4 quotient result error will remain constant at ±1.4% for all 

the SF6 tracer gas tests.
12

2 Results

2.1 Fan Pressurization Testing

Fan pressurization testing provided a basis for determining the garage-to-house air leakage, and 

for evaluating the adequacy of an EPA draft Indoor airPLUS proposal. That draft proposal 

included a house-to-garage pressure differential criterion for determining the airtightness of the 

garage-to-house interface and for determining if a Garage Exhaust fan would be required or not.

The draft proposal language required that the garage-to-house air barrier maintain a pressure 

difference of greater than 45 Pa while the home maintained a 50 Pa pressure difference wrt the 

outdoors. However, the testing results presented here will show that a second criterion is needed 

in combination with the first to eliminate false positives that would allow a not-well-sealed 

garage-to-house interface to pass the first criterion alone. 

All fan pressurization testing was conducted with Minneapolis Blower Door equipment, 

including Model 3 blower door, Ductblaster B, DG-700 digital pressure gauges, Tectite 

automated performance testing software, an 8-channel automated performance testing pressure 

gauge unit operated by Teclog software for monitoring six channels of pressure differential, and 

Zone Pressure Diagnostics (ZPD) software.

Table 2. Listing of Pressure Differential Monitoring Channels

Channel Description

1 House wrt outdoors

2 Garage wrt outdoors

3 Basement wrt outdoors

4 Garage-to-house wall cavity 2 (first floor) wrt outdoors

5 Garage-to-house wall cavity 1 (second floor) wrt outdoors

6 Garage wrt house

Table 3 gives a detailed description of each of the 25 fan pressurization tests conducted on the 

house and garage. Abbreviated forms of the Table 3 descriptions are repeated in Table 4 along 

with the detailed test results.

Referring to Table 3 and Table 4, one can see that Test 1 was conducted by depressurizing the 

house with the house closed to the garage and the garage closed to outside, while Test 2 was 

conducted the same except both garage doors were open during the test. The data in Table 4

show that the house air leakage at –50 Pa (CFM50) wrt outdoors did not go up when the garage 

doors were opened (in fact it went down slightly because of variation between tests, probably 

due to wind effects). This indicated that the house-to-garage air barrier in this house was 

substantially sealed. At 1,763 CFM50 (Test 1), and volume of 53,150 ft3 including the basement, 

the house ACH50 was 1.99. Without the basement volume, the ACH50 would be 2.93. Either 

way, the result was well below the ENERGY STAR Version 3 requirement of ACH50 ≤ 5 for 

IECC climate zone 4. Even at the highest CFM50 measured (2,725 for Test 21), where 80 in.

2 of 

leakage area was added between the house and garage, the house ACH50 was 3.0 including the 

basement.
13

Test 3 was conducted like Test 1 except the door between the house and garage was opened. The 

CFM50 went up substantially in Test 3 compared to Test 1 (340 CFM50, or 19%), indicating that 

the house-to-garage interface was much better sealed than the garage-to-outside interface. 

Table 3. Detailed Description of Each House and Garage Pressurization Test

Test 

# Detailed Description

1 House depressurized, garage closed to out, house closed to garage

2 House depressurized, garage open to out via both garage doors open, house closed to garage

3 House depressurized, garage closed to out, garage open to house via door

4 House depressurized, garage closed to out, house open to garage 10 in.2 via door

5 House depressurized, garage closed to out, house open to garage 15 in.2 via door

6 House depressurized, garage closed to out, house open to garage 25 in.2 via door

7 House depressurized, garage open 60 in.2 to out via window, house open to garage 25 in.2 via door

8 House depressurized, garage open 80 in.2 to out via window, house open to garage 25 in.2 via door

9 House depressurized, garage open 100 in.2 to out via window, house open to garage 25 in.2 via door

10 House depressurized, garage open 120 in.2 to out via window, house open to garage 25 in.2 via door

11 House depressurized, garage open to out via 1 garage door open, house open to garage 25 in.2 via door

12 Garage depressurized through the house, hose open to out via many windows

13 Garage depressurized, house pressure matched to garage pressure (garage/house walls guarded)

14 House depressurized, garage closed to out, house open to garage 50 in.2 via door

15 House depressurized, garage open 100 in.2 to out via window, house open to garage 50 in.2 via door

16 House depressurized, garage open 120 in.2 to out via window, house open to garage 50 in.2 via door

17 House depressurized, garage open 1020 in.2 to out via window, house open to garage 50 in.2 via door

18 House depressurized, garage open to out via 1 garage door open, house open to garage 50 in.2 via door

19 House depressurized, garage closed to out, house open to garage 80 in.2 via door

20 House depressurized, garage open 100 in.2 to out via window, house open to garage 80 in.2 via door

21 House depressurized, garage open 1020 in.2 to out via window, house open to garage 80 in.2 via door

22 Garage depressurized, garage closed to out, house closed to garage

23 Garage depressurized, garage closed to out, house open to garage 15 in.2 via door

24 Garage depressurized, garage closed to out, house open to garage 40 in.2 via door

25 Garage depressurized, garage closed to out, house open to garage 60 in.2 via door
14

Table 4. Results of House and Garage Fan Pressurization Tests

Test 

# Description

House 

Open to 

Garage 

(in.2

)

Garage 

Open to 

Outdoors

(in.2

)

Ca nb R2c ELA

(in.2

) cfm50

cfm50 Diff

% Diff

6% 

Criteria

dPd

Garage 

wrt House 

@ 50 Pa

ES IA

+e 

>45 Pa 

Criteria

1 House 

depressurized 0 0 132.5 0.662 0.9993 94.0 1,763 47 Pass

2 House 

depressurized 0 20,352 127.4 0.670 0.9997 91.4 1,753 –10 –1% 50 Pass

3 House + garage 

depressurized 2,560 0 147.0 0.680 0.9998 107.0 2,103 0

4 House 

depressurized 10 0 141.2 0.653 0.9992 99.0 1,820 39 Fail

5 House 

depressurized 15 0 144.2 0.648 0.9997 100.4 1,818 37 Fail

6 House 

depressurized 25 0 148.0 0.655 0.9995 104.0 1,919 28 Fail

7 House 

depressurized 25 60 157.8 0.660 0.9998 111.7 2,084 40 Fail

8 House 

depressurized 25 80 163.0 0.652 0.9997 114.1 2,085 43 Fail

9 House 

depressurized 25 100 158.4 0.646 0.9991 110.0 1,981 46 Pass

10 House 

depressurized 25 120 158.8 0.647 0.9984 110.4 1,994 47 Pass

11 House 

depressurized 25 10,176 162.7 0.653 0.9978 114.0 2,096 177 9% Fail 50 Pass

12

Garage 

depressurized

through open house

2,560 0 51.4 0.601 0.9993 33.5 539

13

Garage

depressurized, 

house side guarded

0 0 27.6 0.714 0.9976 21.1 450

14 House 

depressurized 50 0 166.8 0.633 0.9913 113.7 1,981 15 Fail
15

Test 

# Description

House 

Open to 

Garage 

(in.2

)

Garage 

Open to 

Outdoors

(in.2

)

Ca nb R2c ELA

(in.2

) cfm50

cfm50 Diff

% Diff

6% 

Criteria

dPd

Garage 

wrt House 

@ 50 Pa

ES IA

+e 

>45 Pa 

Criteria

15 House 

depressurized 50 100 144.7 0.696 0.9963 107.7 2,204 39 Fail

16 House 

depressurized 50 120 200.7 0.609 0.9927 132.4 2,178 40 Fail

17 House 

depressurized 50 1,020 192.7 0.628 0.9960 130.5 2,250 48 Pass

18 House 

depressurized 50 10,176 140.8 0.706 0.9983 106.2 2,229 248 13% Fail 49 Pass

19 House 

depressurized 80 0 191.3 0.594 0.9951 123.6 1,951 7 Fail

20 House 

depressurized 80 100 191.9 0.648 0.9922 133.6 2,418 25 Fail

21 House 

depressurized 80 10,176 234.7 0.627 0.9973 158.7 2,725 774 40% Fail 47 Pass

22 Garage 

depressurized 0 0 31.4 0.649 0.9981 21.9 397 50

23 Garage 

depressurized 15 0 51.7 0.618 0.9989 34.5 579 49

24 Garage 

depressurized 40 0 73.9 0.634 0.9902 50.5 882

25 Garage 

depressurized 60 0 86.8 0.633 0.9932 59.2 1,034

a C = power law curve fit constant

b n = power law curve fit exponent

c R2 = coefficient of determination, indicating how well data points fit the model (1.0 being a perfect fit)

d dP = pressure differential (Pa)

e ES IA+ = ENERGY STAR Indoor airPlus
16

Referring to Tests 12 and 13, this was where the air leakage through the garage-to-house 

interface was determined. Test 12 was conducted by depressurizing the garage through the house 

which was open to outdoors. Thereby, Test 12 measured the air leakage of the entire garage 

enclosure. Test 13 was the same except that the garage-to-house interface was guarded by 

depressurizing the house while the garage was depressurized such that the garage-to-house 

pressure was zero. Thereby, Test 13 measured only the garage-to-outside air leakage because air 

leakage through the garage-to-house interface was eliminated. The difference between those tests 

yielded the garage-to-house air leakage, which was 89 CFM50, as shown in Table 5. The 

resulting garage-to-house ELA was calculated to be 12.4 in2

. As shown in Table 5, these values 

fell between the minimum and maximum values predicted by the ZPD test performed using The 

Energy Conservatory ZPD software. For comparison, that test provided an alternate method of 

estimating airflow between the house and garage zones by adding a hole of known size between 

the zones and analyzing before and after pressure and airflow responses. 

Table 5. Comparison of Test Results Between Guarded Blower Door Test and ZPD Test

Guarded 

Test

ZPD Test

Minimum Maximum

Leakage Area Garage-to-House (in.2) 12.4 9 18

Leakage cfm50 Garage-to House (CFM50) 89 81 156

Having established the leakage area in the garage-to-house interface, further testing was then 

conducted to test the adequacy of the EPA Indoor airPLUS pressure differential criterion. In 

Tests 4, 5, and 6, garage-to-house leakage area was increased by opening the garage-to-house 

door by measured amounts of 10 in.

2

, 15 in.

2

, and 25 in.

2

, respectively. In each case, the 

measured pressure differential failed the pressure differential criterion. Then, in Tests 7 through 

11, garage-to-outside leakage area was incrementally added. By Test 9, where 100 in.

2 of garageto-outside leakage area was added, the measured pressure differential passed the pressure 

differential criterion. In other words, without changing the garage-to-house leakage area, the 

failing interface could be made to pass by adding sufficient garage-to-outside leakage area. The 

blue highlighted cells in Table 4 help focus on this issue of passing and failing.

Note that while this parametric testing was done by making measured modifications to an 

existing construction, the existing construction could reasonably have been randomly constructed 

to result in any of the modified conditions. For example, where gas water heaters are located in 

garages, it would not be uncommon to see a through-wall combustion air vent in the range of 100 

in.

2

. That amount of garage-to-outside leakage area would not necessarily be adequate to cause 

good air quality in the garage, but it was enough to cause a not-well-sealed garage-to-wall 

interface to pass the pressure differential criterion.

Additional testing to confirm those same results was done via Tests 14–18, and Tests 19–21. In 

each case, an initially failing garage-to-house interface was made to pass by adding garage-tooutside leakage area, resulting in a false positive. This is illustrated in Figure 12, which shows 

the inadequacy of house-to-garage pressure differential as a single criterion for house-to-garage 

airtightness.
17

Analysis of the measured data showed that providing a CFM50 difference criterion in 

combination with the pressure differential criterion would eliminate the false positives. The full 

criteria then involved a first and second step. The first step being a garage-to-house pressure 

measurement taken while a house-to-outside CFM50 test was conducted with all operable garage 

openings closed. The second step requires an additional measurement of house-to-outside 

CFM50 with the overhead garage door open, and verifying that the CFM50 with the garage door 

open is not more than a given amount greater than the CFM50 with the garage door closed. The 

second step eliminates false positives that can result in the first step due to certain combinations 

of house-to-garage and garage-to-outside series leakage.

The repeatability of blower door tests using the Model 3 Minneapolis Blower Door with manual 

operation is stated to be ±3%. With computer automated operation, the repeatability is better than 

±3%. So, assuming manual operation, and doubling that to move further away from the noise of 

measurement uncertainty, a reasonable CFM50 criterion amount could be 6%. Thus, the house 

CFM50 measured with the overhead garage door open could not be more than 6% greater than 

the CFM50 with the overhead garage door closed. The resulting rule could read as such:

Verify that the garage-to-house air barrier can maintain a pressure difference of 

greater than 45 Pa while the home maintains a 50 Pa pressure difference with 

respect to the outdoors with all operable garage openings closed during this test 

AND verify that the tested house-to-outside CFM50 with the overhead garage 

door open does not exceed the house-to-outside CFM50 by more than 6% with 

the overhead garage door closed.

Figure 13 illustrates the elimination of false positives found by adding a second criterion limiting 

the increase in house CFM50 to 6% with the overhead garage door open compared to closed.

Symbols to the left of the dashed line of the same color should pass because the change in House 

CFM50 was less than 6%. Symbols to the right of the dashed line of the same color should fail 

because the change in House CFM50 was greater than 6%.
18

0

1

10

100

1000

10000

100000

0 10 20 30 40 50 60

Added garage-to-outside leakage area 

(in2)

House-to-garage pressure differential (Pa)

A "Fail" can "Pass" by increasing garage-tooutside leakage

25 sq.inch added 

house-to-garage 

leakage

50 sq.inch added 

house-to-garage 

leakage area

80 sq.inch added 

house-to-garage 

leakage area

pass-fail line

Figure 12. Test results showing inadequacy of house-to-garage pressure differential as a

single criterion for house-to-garage airtightness

0

1

10

100

1000

10000

100000

1500 2000 2500 3000

Added garage-to-outside leakage area 

(in2)

House cfm50

Keep a "Fail" from "Passing" by adding a 

change-in-CFM50 limit

25 sq.inch added houseto-garage leakage

50 sq.inch added houseto-garage leakage area

80 sq.inch added houseto-garage leakage area

25 sq.in, 6% change in 

cfm50

50 sq.in, 6% change in 

cfm50

80 sq.in, 6% change in 

cfm50

Pass

Figure 13. Elimination of false positives was found by adding a second criterion limiting the 

increase in house CFM50 to 6% with the overhead garage door open compared to closed

Fail Pass

Fail
19

Referring to Figure 14, a plot of the added house-to-garage leakage area illustrates that the house 

effective leakage area was impacted by less than half the amount that was added. This is due to 

the series leakage resistance from the house-to-garage and the garage-to-outside.

0

10

20

30

40

50

60

70

80

90

100

Increase in House Effective Leakage 

0 20 40 60 80 100

Area (in2)

Added house-to-garage leakage area (in2)

Effect of increasing leakage area between house 

and garage on house ELA

Figure 14. House leakage area increased by less than half the

physical house-to-garage opening area added

2.2 Tracer Gas Testing

Tracer gas tests were conducted to determine the fraction of house air that came from the garage 

air, under the six following different operational conditions:

1. Initial baseline (no mechanical ventilation in the garage or house), 12-hour test

2. 165 cfm exhaust ventilation in the house to meet the ASHRAE Standard 62.2-2013 

airflow rate, 24-hour test

3. 165 cfm supply ventilation in the house to meet the ASHRAE Standard 62.2-2013 

airflow rate, 24-hour test

4. 165 cfm exhaust ventilation in the house and 70 cfm exhaust ventilation in the garage 

(EPA Indoor airPLUS Garage Exhaust airflow rate), 24-hour test

5. 330 cfm exhaust ventilation in the house which was twice the ASHRAE Standard 

62.2-2013 airflow rate, 24-hour test

6. Final baseline (no mechanical ventilation in the garage or house), 8-hour test.

Figure 15 shows the outdoor weather conditions of dry bulb temperature, RH, wind speed, and 

wind direction during the six tracer gas testing periods. Outdoor temperature generally ranged 

from lows of 60o

–70oF at night to highs of 80o–90oF during the day. Wind speed ranged between 

0 and 6 mph. Wind direction was most prominently from the southeast.
20

Indoor air environmental conditions during the tracer gas testing are shown in Figure 16. The 

first floor dry bulb temperature was generally about 72o

F, with maximum variation between 70oF

and 75oF. The second floor was warmer and varied more (between 73oF and 80oF) because the 

central system fan serving the second floor was non-functional during the tracer gas testing 

period. For the tracer gas measurements, the first and second floors, with no separation between 

them were intended to be treated as a single zone. Mixing between floors helps them behave 

more as a single zone. Two inline fans with ducts were used to circulate air between the first and 

second floor, located at both stairways. The basement dry bulb temperature was typically about 

67oF, with only small variation between 65oF and 68oF.

In the first and second floor living space, RH typically varied between 40% and 60%. The indoor 

dew point temperature generally varied between 50oF and 58oF throughout the testing, on all 

three levels. RH in the basement was about 70%, due to the cooler temperature (67o

F dry bulb 

and 57oF dew point yields 70% RH). The spike in indoor conditions near the end of the testing 

occurred while the house was being flushed of SF6 between Tests 5 and 6.

Measurement of the environmental conditions of indoor temperature and RH, and outdoor 

temperature, RH, wind speed and wind direction were used only in a qualitative sense, that is, no 

calculations quantitatively required those values. Measurement of these values is useful for 

helping to indicate whether conditions were dramatically different from one test to another, 

possibly providing background explanation for observed differences in results. Therefore, a 

formal measurement uncertainty error analysis with regard to the measured indoor and outdoor 

environmental conditions was not deemed necessary.
21

30

40

50

60

70

80

90

100

8/24/13 12:00

8/25/13 0:00

8/25/13 12:00

8/26/13 0:00

8/26/13 12:00

8/27/13 0:00

8/27/13 12:00

8/28/13 0:00

8/28/13 12:00

8/29/13 0:00

8/29/13 12:00

8/30/13 0:00

Temperature (F) or RH (%)

Outdoor Temperature and RH during six tracer tests

Tout

RHout

0

45

90

135

180

225

270

315

360

0

1

2

3

4

5

6

7

8/24/13 12:00

8/25/13 0:00

8/25/13 12:00

8/26/13 0:00

8/26/13 12:00

8/27/13 0:00

8/27/13 12:00

8/28/13 0:00

8/28/13 12:00

8/29/13 0:00

8/29/13 12:00

8/30/13 0:00

Wind Direction (deg. from north)

Wind speed (mph)

Wind Speed and Direction during six tracer tests

WS WD

1 2 3 4 5 6

Figure 15. Weather conditions during the six tracer gas testing periods
22

60

65

70

75

80

85

90

95

8/24/2013 12:00

8/25/2013 0:00

8/25/2013 12:00

8/26/2013 0:00

8/26/2013 12:00

8/27/2013 0:00

8/27/2013 12:00

8/28/2013 0:00

8/28/2013 12:00

8/29/2013 0:00

8/29/2013 12:00

8/30/2013 0:00

Temperature (F)

Indoor dry bulb temperature during 6 tracer gas tests

1st Main

2nd Main

Basement

Garage

0

10

20

30

40

50

60

70

80

90

100

8/24/2013 12:00

8/25/2013 0:00

8/25/2013 12:00

8/26/2013 0:00

8/26/2013 12:00

8/27/2013 0:00

8/27/2013 12:00

8/28/2013 0:00

8/28/2013 12:00

8/29/2013 0:00

8/29/2013 12:00

8/30/2013 0:00

Relative Humidity (%)

Indoor RH during 6 tracer gas tests

1st Main

2nd Main

Basement

Garage

40

45

50

55

60

65

70

75

8/24/2013 12:00

8/25/2013 0:00

8/25/2013 12:00

8/26/2013 0:00

8/26/2013 12:00

8/27/2013 0:00

8/27/2013 12:00

8/28/2013 0:00

8/28/2013 12:00

8/29/2013 0:00

8/29/2013 12:00

8/30/2013 0:00

Temperature (F)

Indoor dew point temperature during 6 tracer gas tests

1st Main

2nd Main

Basement

Garage

Figure 16. Indoor temperature and humidity conditions during the six tracer gas tests
23

2.2.1 SF6 Test 1: Initial Baseline

Results of the first tracer gas test are shown in Figure 17. This was the initial Baseline test and 

there was no mechanical ventilation in the house or garage. The test started shortly after SF6

injection (10 SCCM) began in the garage. The test ran for about 12 hours. There was essentially 

no wind until sunrise (Figure 15) which then started to change the previously steadily tracking 

pressure differentials due to stack effect alone (Figure 18). The basement pressure spikes of 

about 2 Pa are due to basement pressurization when the cooling system operated (more supply 

air than return air). The garage pressure was about 0.5 Pa positive wrt the house. By the end of 

the test, the garage concentration was 22 ppm and the average of the first main and main

locations was 0.3 ppm. Therefore, the initial baseline test result showed that 1.4% ±1.4% of the 

air in the house had come from the garage (0.3/22 = 0.014, using Eq. 4).

The plots of concentration versus time do not show continuous error bars because of how that 

would obscure the primary time trace. Pressure differential was not used in calculations therefore 

pressure differential error was not calculated or plotted.

The following legend nomenclature was used for the pressure differential plots:

Hs wrt out: House with respect to outside

Ga wrt out: Garage with respect to outside

Bs wrt out: Basement with respect to outside

GaW1 wrt out: First-floor garage wall cavity (adjacent to garage) with respect to outside

GaW2 wrt out: Second-floor garage wall cavity (adjacent to garage attic) with respect to 

outside

Ga wrt Hs: Garage with respect to house

Pressure differential wrt outside was measured in the first-floor wall cavity adjacent to the 

garage, and in the second-floor wall cavity adjacent to the garage attic. These measurements 

were taken to provide indication of the relative airtightness of the outer-side air barrier compared 

to the inner-side air barrier. Results showed that the outer-side (garage-side wallboard) served as 

the primary air barrier for the first-floor wall, while the inner-side (house side wallboard) served 

as the primary air barrier for the second-floor wall. This is best seen in Figure 26.
24

0

5

10

15

20

25

30

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

20212223

01234567

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

SF6 Test 1: Baseline (12 h)

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage (y2-axis)

Figure 17. SF6 test 1, initial Baseline tracer gas test showing that, by the end of the 

24-hour test, about 1.4% of the air in the house came from the garage (0.3/22 = 0.014)

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

1920212223

01234567

Pressure Differential (Pa)

Hour of Day

SF6 Test 1: Baseline (12 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 18. SF6 Test 1, Baseline, monitored pressure differentials showing the garage pressure 

about 0.5 Pa positive with respect to the house

2.2.2 SF6 Test 2: 165 cfm House Exhaust

Results of the second tracer gas test are shown in Figure 19. In this test, 165 cfm of House 

Exhaust was operating. No mechanical ventilation operated in the garage. The test started with 

the garage SF6 concentration where it was after the end of the baseline test. SF6 injection in the 

garage was continuous. The test ran for about 24 hours. Wind speed was up to 4 mph during the 

day and less than 1 mph at night (Figure 15). Without wind, the garage pressure tracked steadily 

at 2 Pa positive with respect to the house (Figure 18). By the end of the test, the results showed 

that 4.6% ±1.4% of the air in the house had come from the garage (0.78/17 = 0.046, using Eq. 4).
25

Where the garage was at a positive pressure with respect to the house, as was the case in the first 

Baseline test and in the two House Exhaust tests, the SF6 concentration next to the first floor 

garage interface wall cavity was higher than in the house. This also confirms that garage air was 

moving into the house under those conditions. In contrast, the SF6 concentration next to the 

second floor wall, adjacent to the vented garage attic, closely tracked the concentration in the 

house. This was logical since the tracer gas was vented to outside from the garage attic. 

0

5

10

15

20

25

30

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

11131517192123

13

57

9

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

SF6 Test 2: 165 cfm House Exhaust

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage

Figure 19. SF6 test 2, 165 cfm House Exhaust ventilation tracer gas test showing that, by the end 

of the 24-hour test, 4.6% ±1.4% of the air in the house came from the garage (0.78/17 = 0.046)

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

1011121314151617181920212223

012345678

Pressure Differential (Pa)

Hour of Day

SF6 Test 2: 165 cfm house Exhaust (24 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 20. SF6 test 2, 165 cfm House Exhaust, monitored pressure differentials showing the 

garage pressure about 2 Pa positive wrt the house
26

2.2.3 SF6 Test 3: 165 cfm House Supply

SF6 tracer gas Test 3 was with 165 cfm of House Supply ventilation operating. No mechanical 

ventilation operated in the garage. The test ran for about 24 hours. Wind speed was about 1 mph 

during the day, and near zero at night (Figure 15). Garage pressure was about 1.5 Pa negative wrt

the house (Figure 18). Although Test 3 started with a significant SF6 concentration in the house 

from the previous exhaust test, by the end of the supply test, the results showed that House 

Supply ventilation had suppressed garage-to-house air transfer such that only 0.5% ±1.4% of the 

air still in the house had come from the garage (0.1/20 = 0.05, using Eq. 4).

0

5

10

15

20

25

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

10121416182022

02468

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

Test 3: 165 cfm House Supply

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage

Figure 21. SF6 Test 3, 165 cfm House Supply ventilation tracer gas test showing that, by the end of 

the 24-hour test, supply ventilation had suppressed essentially all air transfer from the garage to 

the house (0.1/20 = 0.005)

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

9

1011121314151617181920212223

012345678

Pressure Differential (Pa)

Hour of Day

SF6 Test 3: 165 cfm house Supply (24 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 22. SF6 test 3, 165 cfm House Supply, monitored pressure differentials showing the garage 

pressure about 1.5 Pa negative wrt the house
27

2.2.4 SF6 Test 4: 165 cfm House Exhaust and 70 cfm Garage Exhaust

SF6 tracer gas Test 4 was with 165 cfm of House Exhaust and 70 cfm of Garage Exhaust 

operating. The test ran for about 24 hours. Wind speed was up to 5 mph during the day, and near 

zero at night (Figure 15). Garage pressure was about 2 Pa negative wrt the house (Figure 18) and 

about 3.5 Pa negative wrt outdoors. The garage-to-outside pressure relationship was exactly as 

predicted by the garage air leakage curve for 70 cfm exhaust, as shown in Table 4, Test 22. In 

addition, the 5 ppm garage tracer gas concentration, with 70 cfm exhaust and 10 SCCM SF6

injection, agreed with the calculation result shown in Table 1.

While the garage-to-house pressure relationship clearly showed that the 70 cfm Garage Exhaust

had suppressed garage-to-house air transfer, by the end of this test, the results showed that about 

2% ±1.4% of the air in the house had come from the garage (0.1/5.0 = 0.02). That was slightly 

more than for the Baseline test. A possible reason for this could have been that some SF6 being 

exhausted from the garage window, parallel to the front of the house, could have been drawn into 

the house from outdoors by the house-to-outside negative pressure created by the House Exhaust.

0

5

10

15

20

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

9

11131517192123

13579

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

Test 4: 165 cfm House Exhaust + 70 cfm Garage Exhaust

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage

Figure 23. SF6 test 4, 165 cfm House Exhaust and 70 cfm Garage Exhaust tracer gas test showed 

performance that was about the same as for the initial Baseline test (0.1/5.0 = 0.02)

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

1011121314151617181920212223

0123456789

Pressure Differential (Pa)

Hour of Day

SF6 Test 4: 165 cfm house Exhaust + 70 cfm garage Exhaust (24 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 24. SF6 test 4, 165 cfm House Exhaust and 70 cfm Garage Exhaust, monitored pressure 

differentials showing the garage pressure about 2 Pa negative wrt the house
28

2.2.5 SF6 Test 5: 330 cfm House Exhaust

Test 5 was a second House Exhaust test to see what effect a doubling of the House Exhaust used 

in Test 2 would have on the amount of air in the house that came from the garage. In reality, that 

doubling could represent operation of a dryer or range hood, or an additional request for house 

ventilation. Before the test, it was postulated that the fraction of house air that came from the 

garage would not increase much if at all in this case because the garage-to-house interface was 

already known to be well sealed. That is what the test result showed. In fact, the fraction of 

house air that came from the garage decreased from 4.6% ±1.4% to 3.2% ±1.4% when the House 

Exhaust rate was doubled. It appears that the increased house-to-outside negative pressure may 

have had more of an impact than the increased house-to-garage pressure, due to the path of least 

resistance causing a greater fraction of exhaust makeup air to come from outside in the second 

test.

0

5

10

15

20

25

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

11131517192123

135

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

SF6 Test 5: 330 cfm House Exhaust

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage

Figure 25. SF6 test 5, 330 cfm House Exhaust tracer gas test showed that, by the end of the 

24-hour test, 3.2% ±1.4% of the air in the house had come from the garage (0.7/22 = 0.032)

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

6

1011121314151617181920212223

0123456

Pressure Differential (Pa)

Hour of Day

SF6 Test 5: 330 cfm house Exhaust (24 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 26. SF6 test 5, 330 cfm House Exhaust, monitored pressure differentials showing the 

garage pressure about 3.5 Pa positive wrt the house
29

2.2.6 SF6 Test 6: Final Baseline

The availability of the test house allowed for a second Baseline test (Test 6). This test was 

conducted for 8 hours during the daytime, while the first Baseline test (Test 1) was conducted for 

12 hours overnight. In addition, Test 1 was started shortly after the SF6 injection started, thus, 

there was a longer time required to ramp up the concentration than for Test 6 which was started 

when the SF6 concentration in the garage was fairly steady. Between Test 5 and Test 6, the house 

(but not the garage) was flushed of SF6 via open windows and doors, and a blower door fan 

exhausting a large quantity of air. Even with those differences between Baseline tests 1 and 6, 

the result was essentially the same, showing little garage-to-house air transfer due to a wellsealed garage-to-house interface. By the end of Test 6, it was shown that 0.6% ±1.4% of the air 

in the house had come from the garage (0.16/25 = 0.006), compared to 1.4% ±1.4% for Test 1.

The average of both Baseline tests showed that about five times less air in the house came from 

the garage compared to Test 2 with 165 cfm exhaust operating in the house.

21

22

23

24

25

26

27

0.00

0.05

0.10

0.15

0.20

0.25

89

101112131415

Garage SF6 Concentration (ppm)

SF6 Concentration (ppm)

Time of Day (h)

SF6 Test 6: Baseline (8 h)

(10 sccm injection in garage)

1st Main

1st Gar. Wall

2nd Main

2nd Gar. Wall

Basement

Garage

Figure 27. SF6 Test 6, the final Baseline tracer gas test showed again that there was little garageto-house air transfer across the well-sealed garage to house interface (0.16/25 = 0.006)

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

1

2

3

4

5

89

101112131415

Pressure Differential (Pa)

Hour of Day

SF6 Test 6: Baseline (8 h)

Hs wrt out

Ga wrt out

Bs wrt out

GaW1 wrt out

GaW2 wrt out

Ga wrt Hs

Figure 28. SF6 Test 6, Baseline (8 h), monitored pressure differentials showing the garage 

pressure about 1.5 Pa negative wrt the house
30

Figure 29 summarizes the garage wrt house pressure differential for each tracer gas test, 

including the Baseline tests and each ventilation system test. As shown, Garage Exhaust and

House Supply ventilation consistently kept the garage at a negative pressure wrt the house. The 

second Baseline test also showed this relationship, while the first Baseline test showed close to 

neutral pressure conditions, both of which would be indicative of balanced ventilation.

-6

-4

-2

0

2

4

6

1

61

121181241

301361

421481541601661721781841901

961

1021108111411201126113211381

Pressure Differential (Pa)

5 second sample

Garage with respect to House pressure differential by ventilation system test

Test 1: Baseline Test 2: 165 cfm House Exhaust

Test 3: 165 cfm House Supply Test 4: 165 cfm House Exhaust + 70 cfm Garage Exhaust

Test 5: 330 cfm House Exhaust Test 6: Baseline

Figure 29. Pressure differential of the garage wrt house for each tracer gas test

Figure 30 is a summary graph of the average house SF6 concentration divided by the garage SF6

over the last 4 hours of each test. This concentration ratio shows the fraction of air in the house 

that came from the garage. The operation of different ventilation systems showed a consistent 

and steady difference in the fraction of house air that came from the garage. From high to low 

fraction, the order was: House Exhaust, Baseline, House Exhaust+Garage Exhaust, and Supply.
31

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

123456789

1011121314151617181920

SF6 concentration ratio

Sample number (12 minute sample cycle) 

Ratio of house SF6 concentration to garage SF6

concentration for last 4 hours of each test

Test 1: Baseline

Test 2: 165 cfm House 

Exhaust

Test 3: 165 cfm House Supply

Test 4: 165 cfm House Exh + 

70 cfm Garage Exh

Test 5: 330 cfm House 

Exhaust

Test 6: Baseline

Figure 30. Ratio of average house SF6 concentration to garage SF6 concentration for the last 

4 hours of each test, representing the fraction of house air that came from the garage
32

3 Conclusions

In conclusion, the project research questions were answered as follows:

1. What is the measured ELA of the garage-to-house interface?

Measured house-to-garage air leakage, using multipoint computer automation, was 89 

cfm at a 50 Pa pressure differential (89 CFM50). The resulting garage-to-house ELA was 

12.4 in2. These values fell between the minimum and maximum values predicted by a 

separate computerized zone pressure diagnostic test.

2. What is the garage-to-house pressure relationship for a range of house-to-outside 

pressure differentials and for a range of imposed leakage areas between: a) the garage 

and house, and; b) between the garage and outside?

A series of 25 multi-point fan pressurization tests and additional zone pressure diagnostic 

testing characterized the garage and house air leakage, the garage-to-house air leakage, 

and garage and house pressure relationships to each other and to outdoors using 

automated fan pressurization and pressure monitoring techniques. The results are given in 

detail in Table 3 and Table 4. For example, with the house at –50 Pa wrt outdoors, and no 

imposed house-to-garage or garage-to-outside leakage, the garage-to-house pressure 

differential was –47 Pa. With 25 in.

2 house-to-garage leakage imposed, the garage-tohouse pressure dropped to –28 Pa, then with 100 in.

2 garage-to-outside leakage imposed, 

the garage-to-house pressure raised back up to –46 Pa. This example showed that a 

relatively leaky house-to-garage interface can fail or pass a single garage-to-house 

pressure differential test criterion depending on the actual garage-to-outside leakiness.

3. Is there a simple test criterion that could define an adequately sealed garage-to-house 

interface?

Testing to evaluate the adequacy of the draft EPA Indoor airPLUS pressure differential 

criterion showed that using a CFM50 difference criterion in combination with the 

planned pressure differential criterion would eliminate false positives. In a first step of 

the test, a garage-to-house pressure measurement is taken while a house-to-outside 

CFM50 test is being conducted with all operable garage openings closed. The garage-tohouse pressure differential must be greater than 45 Pa. A new second step would require 

an additional measurement of house-to-outside CFM50 with the overhead garage door 

open, and verifying that the CFM50 with the garage door open is not more than 6% 

greater than the CFM50 with the garage door closed. The second step eliminates false 

positives that can result in the first step due to certain combinations of house-to-garage 

and garage-to-outside series leakage.

For this test house, constructed by a production builder to comply with the 2009 IRC and 

IECC, the garage-to-house pressure differential was 47 Pa with the house at –50 Pa wrt

outdoors and all operable garage openings closed, and the house CFM50 air leakage did 

not increase when tested with the overhead garage door open.
33

4. What is the fraction of house living space air that comes from the garage, and what is the 

house-to-garage pressure relationship, under operation of different whole-house 

ventilation systems, and with operation of the 70 cfm EPA Indoor airPLUS compliant 

Garage Exhaust?

Six tracer gas tests conducted to determine the fraction of house air that came from the garage 

under different operating conditions yielded the following conclusions:

• The operation of different ventilation systems showed a consistent and steady difference 

in the fraction of house air that came from the garage. From high to low fraction, the 

order was: House Exhaust, Baseline, House Exhaust+Garage Exhaust, and Supply.

• The initial Baseline test showed that 1.4% ±1.4% of the air in the house came from the 

garage. The house pressure was about 0.5 Pa negative wrt the garage. The final Baseline 

test showed that 0.6% ±1.4% of the air in the house came from the garage. Averaging 

both Baseline tests revealed that about 1% ±1.4% of the air in the house came from the 

garage when no mechanical ventilation system was operating, or close to five times less 

than when operating 165 cfm of House Exhaust ventilation.

• The 165 cfm House Exhaust ventilation test showed that 4.6% ±1.4% of the air in the 

house came from the garage. The house pressure was about 2 Pa negative wrt the garage.

• The 165 cfm House Supply ventilation test showed that the supply ventilation suppressed 

essentially all air transfer from the garage to the house. The house pressure maintained 

about 1.5 Pa positive wrt the garage.

• The 165 cfm House Exhaust plus 70 cfm Garage Exhaust test showed performance that 

was about the same as the initial Baseline test; however, it is possible that some tracer gas 

being exhausted to outdoors from the garage may have come into the house because of 

house depressurization due to the house exhaust ventilation. Garage Exhaust of 70 cfm 

was sufficient to depressurize the garage 2 Pa wrt the house and thereby preclude garageto-house air transfer.

• The 330 cfm House Exhaust test showed that about 3.2% ±1.4% of the air in the house 

had come from the garage. The house pressure was about 3.5 Pa negative wrt the garage.

While the relative characteristics of this house may not represent the entire population of new 

construction configurations and airtightness levels (house and garage) throughout the country, 

the technical approach was conservative and should reasonably extend the usefulness of the 

results to a large spectrum of house configurations from this set of parametric tests in this one 

house. Based on the results of this testing, the two-step garage-to-house air leakage test protocol

described above is recommended where whole-house exhaust ventilation is employed. For 

houses employing whole-house supply ventilation (positive pressure) or balanced ventilation 

(same pressure effect as the Baseline condition), adherence to the EPA Indoor airPLUS house-togarage air sealing requirements should be sufficient to expect little to no garage-to-house air 

transfer.
26

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