Laboratory Testing of 

Aerosol for Enclosure 

Air Sealing

Curtis Harrington and Mark Modera

Western Cooling Efficiency Center – UC Davis

Building Industry Research Alliance

May 2012
ii

This report received minimal editorial review at NREL

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Laboratory Testing of Aerosol for Enclosure Air Sealing

Prepared for: 

Building America

Building Technologies Program

Office of Energy Efficiency and Renewable Energy 

U.S. Department of Energy

Prepared by:

Curtis Harrington and Mark Modera

Western Cooling Efficiency Center – UC Davis

Building Industry Research Alliance

7407 Tam O’Shanter Dr.

Stockton, CA 95210

NREL Technical Monitor: Chuck Booten

Prepared Under Subcontract Number: KNDJ-0-40343-00

May 2012
iv

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v

Contents

Table of Figures .......................................................................................................................................... v

Table of Tables ............................................................................................................................................ v

Executive Summary................................................................................................................................... vi

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

2 Experimental Methods ......................................................................................................................... 2

2.1 Test Apparatus.....................................................................................................................2

2.2 Analysis Method ..................................................................................................................3

2.3 Results..................................................................................................................................4

3 Discussion............................................................................................................................................. 9

4 Conclusions ........................................................................................................................................ 10

References................................................................................................................................................. 11

Table of Figures

Figure 1. Photos showing the enclosure and leak panels used for the small-scale tests .................. 2

Figure 2. Dimensioned views of the enclosure showing the various leak locations. Each Leak 

panel, illustrated by the green squares, contained six slot leaks, and the sealant was 

introduced through the injection hole illustraed by the green circle on the front. ....................... 2

Figure 3. Leakage profiles for each of the nine tests.............................................................................. 5

Figure 4. Sealant deposit pattern on back low panel for test 1 and 2 ................................................... 6

Figure 5. Typical Pressure profiles inside the enclosure during tests with no pressure control, and 

tests controlled at 100 Pa and 50 Pa .................................................................................................. 6

Figure 6. Average sealant distribution for test at various pressures and 25 ccm sealant injection 

rate ......................................................................................................................................................... 7

Figure 7. Impact of particle size on sealant use and deposition............................................................ 8

Table of Tables

Table 1. Test Protocol Used for Each of the Nine Tests ......................................................................... 5

Unless otherwise indicated, all figures and tables were created by the Building Industry 

Research Alliance.
vi

Executive Summary

Space conditioning energy use can be significantly reduced by addressing uncontrolled 

infiltration and exfiltration through the envelope of a building. A process for improving the 

airtightness of a building envelope by sealing shell leaks with an aerosol sealing technology is 

presented. Retrofit and new construction applications are possible with this process during 

occupancy changes, the rough-in stage of new construction, or possibly from attics or 

crawlspaces in occupied homes. The initial research was limited to small-scale testing in a 

laboratory environment, and the results were very promising. All tests sealed the test enclosure 

from approximately 41 in.2 of open leakage area to nearly 0 in. of leakage area in less than 30 

min. This research will help the development of an application protocol for aerosol sealing of 

building shells that will eventually be demonstrated on buildings in retrofit and new construction.
1

1 Introduction and Background

Residential building shells are notoriously leaky, causing unintended flows between conditioned 

and unconditioned spaces that result in additional loads for the heating and air-conditioning 

equipment to address. One study shows that houses built in the 1990s can have as much as 180 

in.

2 of leakage area for a 1500-ft2 home (Sherman and Dickerhoff 1998). A significant effort has 

been made to reduce the leaks in building shells withh current construction practices, but the 

problems of high labor costs, constant vigilance, and quality control remain. The objective of this 

research is to develop and demonstrate a remote sealing process that uses aerosolized sealant to 

simultaneously measure, find, and seal leaks in a building envelope shell in an efficient and cost 

effective manner. The tested process involved pressurizing a space with a fog of sealant particles 

that travel to, and as they escape, seal the leaks.

A similar process, developed by Lawrence Berkeley National Laboratory and commercialized 

under the name Aeroseal, has been used to seal leaks in ducts with great success. The process 

injects a solution of polyvinyl acetate sealant and water into a high-pressure airstream to produce 

tiny droplets. A calibrated fan and heater produce the carrier flow that sends the sealant through 

the duct system, and evaporates the water surrounding the sealant particle. Tests at Lawrence 

Berkeley National Laboratory of the particle size produced by a compressed-air nozzle similar to 

the one used in the commercial Aeroseal machine (used for our testing) generated particles with 

a mean diameter around 7 μm. With all catastrophic leaks repaired, such as disconnected ducts, 

the aerosol sealants are shown to be capable of sealing approximately 80% of the leaks 

encountered in residential homes (Modera et al. 1996). In general, the sealing rate in duct 

applications was shown to vary with the width (or smallest dimension) of the leak squared 

(Carrie and Modera 1998). Thus although there is no well-established maximum leak size, this 

efficiency creates practical limitations on the size leak that can be sealed. For example, a 1⁄8-in.

gap seals 64 times faster than a 1-in. gap, although 1-in. gaps have been sealed. For reference 

purposes, the company that sells the equipment for duct sealing quotes maximum practical leak 

sizes between 3⁄8 in. and 5⁄8 in. across. The work presented in this report looks at a similar process 

applied instead in a nominally quiescent environment without the use of a carrier flow to deliver 

the aerosol sealant to the location of the leaks.
2

2 Experimental Methods

2.1 Test Apparatus

The Western Cooling Efficiency Center constructed an 8-ft × 8-ft × 4-ft enclosure with leak 

panels distributed at various locations around the shell (Figure 1). Figure 2 presents an 

illustration of the location of the leak panels installed. The approximate size of each leak is 0.1 to 

0.12 in. × 10-in. × 0.125 in. (H × W × D); and each leak panel has six leaks. The height of each 

leak was meant to be representative of a typical leak in a building shell, but the depth is much 

shorter than what is expected to be found in buildings, so the leaks in the enclosure would tend to 

seal more slowly. The total measured leakage was approximately 41 in.2 of open leakage area. A 

14-in. diameter hole was used as the injection site to introduce the sealant fog near the top of the 

enclosure (see Figure 2).

Figure 1. Photos showing the enclosure and leak panels used for the small-scale tests

Figure 2. Dimensioned views of the enclosure showing the various leak locations. Each leak

panel, illustrated by the green squares, contained six slot leaks, and the sealant was introduced 

through the injection hole illustrated by the green circle on the front.

Front

Side

Back

Top
3 

2.2 Analysis Method

The performance of the remote sealing technology was evaluated using three primary metrics: 

(1) the time needed to seal the enclosure; (2) particle deposition inside the enclosure; and (3) the 

uniformity of sealant deposition at the leaks. These performance metrics were used to evaluate 

several independent parameters to understand their effects. The parameters evaluated included 

the pressure inside the enclosure, the flow rate of sealant injected, and the size of the particles 

injected.

The commercial Aeroseal machine, although probably not appropriate for building applications, 

was used for our initial tests of sealing building shells. It includes instrumentation for measuring 

differential pressure between the enclosure and ambient, as well as for measuring the airflow, 

thereby facilitating continuous monitoring of leakage area during the sealing process. The 

leakage area was computed using Equation 1 (Carrie and Modera 2002) and Equation 2

(Batchelor 1967). 

Q = ELAref ∙ �2 ∙ ∆P

ρ ∙ � ∆P∆Pref�

n

Equation 1 

LA = ELA

0.6

Equation 2

 

Where 

Q = the measured airflow rate, 

ELAref = the effective leakage area, 

∆P = the pressure measured across the leak, 

∆Pref = a reference pressure (chosen to be 25 Pa), 

ρ = the air density, 

n = the flow exponent (typically 0.5 for an orifice), and 

LA = the leakage area. 

The ELAref of a leak is the area of a perfect nozzle that at some reference pressure will produce 

the same flow as the leak at that pressure. It can be shown both experimentally and through 

theoretical calculations that the ELA is related to the actual leakage area of an orifice by a factor 

of 0.6 (Batchelor 1967). 

A mass balance was used to determine where the sealant is ultimately deposited. Using a scale 

with a 0.001 gram resolution, the weight of various materials before and after sealing allowed us 

to track the fraction of sealant that was lost from settling or turbulent deposition onto surfaces. 

These materials included a sheet of plastic placed on the bottom of the test enclosure, the plastic 

tubing used to transport the sealant from the generation point to the enclosure, and plastic sheets 

placed on the walls and ceiling. In addition, the sealant deposited in each panel leak was 

determined by removing the sealant in and around the leak and then weighing the removed 
4

sealant. The results for different panels were to get a feel for the particle distribution inside the 

enclosure. Errors may have been introduced by not completely removing all sealant from the 

panels, the sample sections of plastic used for measuring wall and ceiling deposition not being 

representative of the entire surface, and using the manufacturer’s calibration for the sealant flow 

rates. Assuming the pump calibration is reasonably accurate, the overall error in the 

measurements is expected to be within ±5%.

The approach for the first stage of development employed the Aeroseal equipment and applied it 

to sealing the test enclosure. Initially, it was expected that the particles produced by the Aeroseal 

equipment would be too large to allow for sufficient particle suspension. This was not the case, 

however, and the leaks were more than sufficiently sealed in the initial tests, though observations 

in the small-scale tests led to further research on the impact of reducing particle size. In addition 

to reducing particle size, oscillating fans could be used to assist in keeping the particles 

suspended and to make the indoor-air particle distribution more uniform in an actual application.

The performance of each test was evaluated using the leakage versus time profiles, as well as the 

analyses of sealant use efficiency quantified by the mass balance of sealant materials (fraction on 

floor, in leaks, on walls, and lost through leaks).

The independent variables investigated included:

• Average particle size (controlled by sealant dilution)

• Enclosure pressure control

• Sealant injection rate.

The dependent variables that were used to quantify performance included:

• Sealing rate

• Sealing uniformity (comparison of the amount of sealant deposited on panels in different 

locations)

• Sealant use efficiency (fraction that settles on the floor and other surfaces, versus 

deposited in leaks).

2.3 Results

Several tests of the envelope sealing process were performed, all of which showed promising 

results, sealing the enclosure in less than 30 min. Each test was performed under different 

conditions to study the impacts of the independent variables on the sealing parameters (Table 1).

Figure 3 shows the leakage profiles for each of the nine tests in the enclosure. All tests 

successfully sealed the enclosure to nearly zero leakage in less than 30 min. Note that, at the 

beginning of each test, the sealant lines were first purged of water before sealant reached the 

injection nozzle, causing a slight delay at the beginning of each test, which for 25 ccm tests was 

about 5 min and for the 100 ccm test was about 2 min.

The leakage profiles show that the sealant injection rate has a significant impact on sealing time, 

whereas controlling the pressure inside the enclosure had a less significant impact. Tests 

performed at a 25 ccm injection rate at various pressures all sealed the enclosure in 13–15 min, 

whereas injecting sealant at 100 ccm sealed the enclosure in 6 min. Reducing sealant particle size 
5

by diluting the sealant with water also significantly extended the sealing time. This is due to the 

reduced solid sealant injection rate associated with diluting without adjusting the pump rate. In 

the test with diluted sealant, the enclosure sealed in approximately 28 min (Figure 3).

Table 1. Test Protocol Used for Each of the Nine Tests

Test 

Number

Box Pressure 

(Pa)

Sealant Injection Rate 

(ccm) Sealant Dilution

1 No pressure/flow control 100 No Dilution

2 100 25 No Dilution

3 No pressure/flow control 25 No Dilution

4 50 25 No Dilution

5 100 25 No Dilution

6 50 25 No Dilution

7 100 25 No Dilution

8 50 25 No Dilution

9 100 25 1 part sealant/1 part water

Figure 3. Leakage profiles for each of the nine tests

The sealant deposition pattern could be a quick indication of the sealant use efficiency. Figure 4

shows the sealant deposition pattern observed during a high sealant flow application and another 

at low sealant flow application. The large spread of sealant across the leak in the 100 ccm test 

indicates that more sealant was deposited in and around the leak. The deposition patterns for all 

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

50.0

0 5 10 15 20 25 30 35

Leakage Area (in.2)

Time (min)

First Test

Second Test

Third Test

Fourth Test

Fifth Test

Sixth Test

Seventh Test

Eighth Test

Ninth Test
6 

tests performed at a 25 ccm injection rate were similar, showing a much cleaner seal. We believe 

that this implies better sealant use efficiency at lower sealant injection flows. Comparing the 

sealant deposition in and around the leaks for different panels (leak locations) showed very little 

variance. There was only a 1%–2% variation in the mass of sealant deposited in any of the leak 

panels distributed around the enclosure, suggesting very good particle distribution and sealing 

uniformity for all tests performed.

Figure 4. Sealant deposit pattern on back low panel for tests 1 and 2

The pressure was regulated by a calibrated fan that controlled the airflow delivered to the test 

enclosure. Three operating pressures were studied in the small-scale tests: (1) no pressure control 

(which effectively allows the fan curve of the Aeroseal machine to control the injection flow); 

(2) manual flow control to maintain 100 Pa pressure differential: and (3) manual flow control to 

maintain 50 Pa pressure differential. Because a very low leakage level was achieved by injecting 

aerosol sealant, the pressure inside the enclosure became difficult to control as the flow 

approached the minimum achievable by the equipment (Figure 5). Better control of the pressure 

inside building shells for the duration of the installation of aerosol sealant will be needed to 

avoid overpressurizing the space. 

Figure 5. Typical pressure profiles inside the enclosure during tests with no pressure control, and 

tests controlled at 100 Pa and 50 Pa

Typical pattern for 

100 ccm injection rate

Typical pattern for 

25 ccm injection 

rate
7

The mass balance analysis allows for accurate tracking of where the sealant is ultimately 

deposited. The sealant distributions in Figure 6 show how pressure control affects the sealing 

process. There is a clear trend showing that lower enclosure pressure leads to less sealant 

deposited in and around the leaks, more sealant depositing on the floor, less sealant depositing on 

the walls and ceiling, and more sealant being blown through the leaks. Although most sealant 

injected was blown through the leaks, it is expected that the geometry of leaks in typical 

buildings will be different than the test enclosure. The longer flow path of typical leaks in 

buildings is expected to reduce the amount of sealant blown through and, therefore, improve the 

efficiency of sealant use. The typical building leak sealed during this process would be at the 

joints and seams between building materials that are much deeper then the leaks tested in the 

laboratory enclosure. Deeper leaks reduce the angle of trajectory that would allow a particle to 

pass through the leak without impacting a wall and depositing. Laboratory tests of aerosol duct 

sealing showed similar results, measuring about 25% of sealant depositing in a slot leak at 100 

Pa (Carrie and Modera 2002), whereas our tests show about 21% of sealant depositing in the leak 

under the same conditions. The machine generating the aerosol in Carrie and Modera (2002) was 

a different injector that produced larger particle sizes. Smaller particles lead to more sealant 

blown through the leak, which may account for the less efficient sealant deposition in our tests.

Figure 6. Average sealant distribution for test at various pressures and 25 ccm sealant injection 

rate

Manipulating sealant particle size was intended to reduce particle settling in the enclosure. To 

generate smaller particles, the sealant mixture was diluted with a one-to-one mixture of sealant 

and water, thereby reducing the particle diameter by about 20% on average. Figure 7 compares 

the sealant use and distribution during the test of diluted sealant and other tests at similar 

pressures. The diluted test used slightly more sealant than the other tests with a significant 

increase in the amount that was blown through leaks. Surprisingly, there was no impact on the 

amount of sealant that settled on the ground compared to the 100 Pascal tests. Because smaller 

particles have longer settling times, it was expected that less sealant would settle on the floor and 

the sealant particles would distribute better throughout the test enclosure. This was not observed 

in the small-scale tests. This could be the result of the enclosure size, but more likely is due to 

the longer injection period. Another test that uses the same rate of solid sealant injection with the 

smaller sealant particles should be conducted.
8

Figure 7. Impact of particle size on sealant use and deposition
9

3 Discussion

The small-scale tests of a remote sealing process using aerosol sealant were very successful, and 

were as good as, or better than, that experienced in ducts. The sensitivity tests show that reducing 

the pressure in the enclosure increased the sealant required to seal the same leaks, principally by 

reducing excess deposition around the leaks, more than making up for a bit more sealant

deposition on the floor. Lower pressures also reduced the amount of sealant that deposits on the 

ceiling and walls. Most small-scale tests were performed at 50 Pa and 100 Pa, as these are the 

expected operating pressures for a test in an actual building. The tests results at these pressures 

were very similar, making it difficult to conclude which will be better in actual buildings.

One problem with the small-scale testing performed was that the size of the space does not allow 

us to see all the effects of changing a given parameter. For example, smaller particles could be 

more beneficial in a space with larger horizontal dimensions (more floor area, but the same 

ceiling height). For similar reasons, oscillating fans for reducing particle settling times were not 

tested, although they could be useful for applications in larger spaces. Particle size reduction and 

oscillating fans will be explored further in tests of the sealing process in actual buildings.

This technology is expected to cost much less than manually sealing a home and to be much 

more effective, though more research is needed for better cost estimates. Assuming the sealing 

rate is similar in an actual application, the results of the small-scale tests show that a typical 

1500-ft2 house would require less than 1⁄2 gal of sealant solution to seal the leaks. The preparation 

of a house for sealing includes setting up a blower door, covering the floor with plastic, taping 

off leaks that we do not want to seal (e.g., gaps between double-hung windows), and taping off 

exhaust ducts and flues. The sealing process would take a technician about four hours to prepare 

and complete. The sealant used for duct sealing is sold for about $50/gal, so with a billing rate of 

$50/h for the technician, a reasonable cost estimate for sealing a 1500-ft2 home might be $250. 
10

4 Conclusions

Sealing buildings shells can have a large impact on building energy use, as it reduces

uncontrolled airflows between conditioned and unconditioned spaces. A method for quickly 

sealing building shells using an aerosol sealant has been demonstrated in a small, nominally 

quiescent test enclosure with very promising results. Several tests were performed to test the 

sensitivity of several independent variables on the sealing process, including internal enclosure 

pressure and particle size. In all tests the enclosure was sealed from 41 in.2 of total leakage area 

to less than 1 in.2 of total leakage area in less than 30 min. This laboratory testing of the 

technology will be used to develop an application protocol for aerosol sealing of building shells.

Further research is planned to demonstrate the shell sealing protocol in retrofit and newconstruction applications.
11

References

Batchelor, G.K. (1967). An Introduction to Fluid Dynamics. Cambridge University.

Carrie, F.R.; Modera, M.P. (1998). “Particle Deposition in a Two-Dimensional Slot from a 

Transverse Stream.” Aerosol Science and Technology vol. 28, pp. 235–246.

Carrie, F.R.; Modera, M.P. (2002). “Experimental Investigation of Aerosol Deposition on Slotand Joint-Type Leaks.” Aerosol Science vol. 33, pp. 1447–1462.

Modera, M.P.; Dickerhoff, D.; Nilssen, O.; Orlando, E. Duquette, H.; Geyselaers, J. (1996). 

“Residential Field Testing of an Aerosol-Based Technology for Sealing Ductwork.” Proceedings 

of ACEEE Summer Study, Pacific Grove, CA, 1996.

Sherman, M.; Dickerhoff, D. (1998). Air-Tightness of US Dwellings, L.B.N.L. Energy 

Performance of Building Group, Editor.
DOE/GO-102012-3515 ▪ May 2012

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