NBSIR 76-1063

Air Leakage Measurements in a

Mobile Home

Charles M. Hunt

Stephen J. Treado

Bradley A. Peavy

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Issued August 1976

Prepared for The Federal Energy Administration

1200 Pennsylvania Avenue, N. W.

Washington, D. C. 20461

NBSIR 76-1063

AIR LEAKAGE MEASUREMENTS IN A

MOBILE HOME

Charles M. Hunt

Stephen J. Treado

Bradley A. Peavy

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

July 1976

Final Report

Issued August 1 976

Prepared for The Federal Energy Administration

1200 Pennsylvania Avenue, N. W.

Washington, D. C. 20234

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director

Air Leakage Measurements in a Mobile Home

by

C. M. Hunt, S. J. Treado, and B. A. Peavy

ABSTRACT

Air leakage measurements were made in a mobile home using sulfur

hexafluoride (SFg) as a tracer gas. The home was located in an environmental chamber where it was possible to measure and control the temperature outside the home. The effect on infiltration rate of a number of

variables was determined. These included inside-outside temperature difference, simulated wind, installation of storm windows, opening of doors,

and operation of the furnace fan. Experiments were also performed in

which a fan was sealed to an opening in the house and inside-outside pressure difference measured as the fan blew air into or out of the structure

at measured rates.

Key Words: Air infiltration measurement; air leakage measurement; mobile home tightness; sulfur hexafluoride tracer measurement

i

Air Leakage Measurements in a Mobile Home

by

C. M. Hunt, S. J. Treado, and B. A. Peavy

1. Introduction

Air leakage is one of the means by which energy is lost by buildings.

It is a function of building tightness, weather conditions, and other factors. This report describes some air leakage measurements of a mobile

home located in an environmental chamber. The method for determining air

leakage employs a sulfur hexafluoride (SF^) tracer dilution technique.

In addition to tracer dilution measurements of infiltration, pressurization and depressurization measurements were made on the home. Strieker

[1] and Tamura [2] describe experiments in which the inside-outside pressure differences of houses were measured when the houses were depressurized with a fan to give a measure of building tightness and to locate

leaks . Slight variations of their procedure have been applied to the

mobile home.

Mobile homes at present represent the fastest growing segment of the

housing market. However, data on the energy utilization of this type of

structure is meager. These air leakage measurements are a part of an FEA- _ sponsored study to evaluate energy utilization in a home built in accordance with ANSI Mobile Home Standard A119.1 (197A) . The study was intended

to provide a data base for developing energy conservation requirements for

inclusion in the mobile home standard. This work was performed to assist

the National Fire Protection Association Committee which developed Standard NFPA 501B, which was a prototype for ANSI A119.1. The main part of

the study showing energy utilization in the mobile home is presented in a separate report. The present report considers the air leakage aspects of

the problem.

2. Experimental Procedures

a. Description of Test House

The test house was a nominal 50 ft x 12 ft (15.2 m x 3.7 m) mobile

home with a floor plan as shown in Figure 1. The floor area was 515 ft^

(48 m2) and the ceiling height 7 ft (2.1 m), giving a gross inside volume

of about 3,600 ft-^ (102 m^). The mobile home was equipped with storm windows which fitted inside of louvered jalousie-type windows rather than

outside where storm windows are normally placed. The combined window area

was about 65 ft^ (6 m2) , or approximately 12 percent of the floor area or

3 1/2 percent of the total floor, ceiling, and wall area. Cabinets and

closets represented about 6 1/2 percent of the gross internal volume of

the living space. There was also an airspace between the ceiling and roof

which is estimated to represent another 5 or 6 percent of this volume.
The home was heated by a gas furnace with a forced warm air distribution system leading to the rooms. The locations of the floor registers

are shown in Figure 1. The furnace drew combustion air from a duct leading from the roof and did not communicate directly with the living space.

The home was placed in an environmental chamber of 70,000 ft"^ (1,980

15 m-^) volume, and the inside and outside temperatures were controlled

and measured. A number of views of the home are shown in Figures 2, 3,

and 4. The skirt around the lower part of the structure was absent during the earlier tracer tests in which infiltration rate as a function of

inside-outside temperature difference was measured. Measurements of the

effect of operating the furnace fan on infiltration rate were made after

the skirt was installed.

b. Infiltration Measurements

An amount of SF^ tracer gas (usually 1 ml or less) was introduced

into the furnace fan and distributed throughout the house. Tracer con- centration was measured as a function of time using a gas chromatograph

equipped with an electron capture detector, and infiltration rate was

estimated from the rate of dilution of the tracer. Samples were introduced into the chromatograph by means of an automated sampling system

and measured within a few seconds. The system has been described previously [3]

.

Replicate samples were collected every 10 minutes through a network

of 1/8 in. (0.32 cm) ID tubes of equal length leading from each room (network sampling) . Samples were also taken from one of the supply registers

(supply sampling). In addition, samples were taken from the environmental

chamber immediately outside the house from a point 2 1/2 ft (0.76 m) above

ground level and just above the roof level as a check on outside concentration of tracer. This concentration must be small if reentry of tracer

into the home is to be neglected.

Infiltration was calculated from tracer concentration measurements

by the relationship

:

c. V

In — = - :^ t = - ^ t (1)

io

indoor concentration of tracer at time t, in hours

initial concentration of tracer

rate at which outside air enters the structure

effective inside volume of the structure

the infiltration rate, in air changes per hour

2

where

V =

oV =
If the forces producing air leakage remains constant during the measurement interval, when In c^/c^^q is plotted against time, the relationship

calls for a straight line in which the negative slope is proportional to

infiltration rate. A simple derivation of equation 1 is given elsewhere

[4]. The model assumes complete mixing, and to approach this condition

the furnace fan was operated continuously.

c. Fan Experiments

To simulate some of the effects of wind load, eight fans were directed

against the rear side of the house from a distance of 5 ft (1.5 m) . Four

of the fans were 1/A-hp (187 watts output) 1,100-rpm pedestal fans with

27-inch (0.69 m) blades. Four were 1/3-hp (249 watts output) 1,725-rpm

smoke ejector fans with 16-in. (0.41 m) blades. Some of the fans are

shown in Figure 3

.

d. Pressurization-Depressurization Experiments

To pressurize the home the kitchen exhaust fan was removed from its

mounting, and a 1 1/2-hp (1.1 KW) centrifugal blower mounted outside was

connected to the opening through a 1-ft (0.3 m) ID round flexible duct.

To depressurize, the blower was placed inside the house and the process

reversed. The delivery rate of the blower was controlled with a damper

and measured by determining the pressure drop across a 6-inch (.15 m)

calibrated orifice mounted on a short cylindrical duct 1 ft (0.3 m) long

and 1 ft in diameter, which was attached to the blower intake. Pressure

differences between the inside and outside of the home were measured with

a Hook gage to an accuracy of about 0.002 in. W.G.

3. Results

a. Infiltration Rates and Inside-Outside Temperature Differences

Measured infiltration rates and average inside-outside temperature

differences are given in Table 1. Most values were between 0.4 and 0.6

air changes per hour with a trend towards increasing infiltration rates

with increasing temperature difference. The two methods of sampling (network and supply) gave results which were essentially in agreement, indicating that tracer distribution was nearly uniform. For computational

purposes, the data have been fitted to an empirical linear regression

equation. For network sampling the relationship was:

^ = 0.367 + 0.00560 (T^ " T^) , a = 0.070 (2)

where

T^ = average indoor temperature, °C

3
T average outdoor temperature, °C

o

a standard deviation of the individual points from

the regression line

For supply sampling the relationship was:

0.356 + 0.00612 (T - T ), a 0.066 (3)

or a composite relationship for all the data was:

-5 = 0.362 + 0.00586 (T. - T ), a 0.080 (4)

The data are also shown graphically in Figures 5 and 6. The random scatter of points may be seen by inspection of the graphs as well as from the

standard deviations which are of the order of 0.06 to 0.08 air changes

per hour. This represents the combined effect of imperfect mixing and

sampling as well as instrumental errors. It is also believed that initial runs often tended to be more divergent than subsequent runs on any

given day. This suggests that some marginal reduction in scatter might

be obtained by increasing the warm-up time of the instrument and allowing more time for the tracer to distribute itself. The present procedure

has been to allow at least an hour for instrument warm-up and 10 to 20

minutes for distribution of tracer throughout the house.

b. Fan Experiments

Infiltration rates obtained with the eight fans operating are given

in Table 2 and are presented graphically in Figure 7. For purposes of

comparison an average regression line corresponding to equation 4 is drawn

in Figure 7. Most of the values with the fans operating were between

0.55 and 0.7 air changes per hour, about 0.1 to 0.3 air changes per hour

higher than the average values with no fans operating.

The average air velocity with the fans operating was about 8 mi/hr

as measured about 6 inches from the house with a hot-wire anemometer.

This was an average of a 46-point scan. It should be pointed out that

fans directed against the side of the house do not simulate all of the

effects of a natural 8 mi/hr wind. However, the experiment demonstrates

that infiltration rates were increased by this air movement.

c. Effect of Storm Windows

Four infiltration measurements were made with the storm windows installed, both with and without the outside fans operating. The results

are summarized in Table 3, and they are also included in Figure 7. The

effect of storm windows on infiltration rate was quite small.

4
d. Tracer Measurements With Doors Open

As noted in Tables 1 and 2, there were brief door openings during

some of the measurements. This raises the question of how much door

opening influences infiltration rate. The problem is also of interest

from the point of view of fuel economy. To obtain an approximate estimate of this effect, measurements were made with one or both doors left

open. It should be pointed out that a high degree of precision was not

obtained under these conditions, because at high infiltration rates the

mixing of tracer could not keep pace with the rate of infiltration. However, the assumption was made that the rate of decrease in tracer con- centration during the first 3 to 5 minutes of the measurement reflected

the true infiltration rate. The rationale for this assumption is that,

for a given infiltration rate, plots of concentration vs. time for the cases of perfect mixing and partial mixing nearly coincide in the early

stages of the air exchange process [4] . Under this assumption air ex- change rates of the order of 2 to 4 air changes per hour were obtained

with the front door open. This is roughly 4 to 8 times the normal rate.

For a 3,600 ft^ (102 m^) house this corresponds to 120 to 240 cfm (0.057

to 0.113 m^/sec) . With both doors left open and with the outside fans

operating air exchange rates as high as 2,000 cfm (2.94 m-^/sec) were estimated. Thus, with doors left open air exchange could be a major part of

the heating load.

While an open door may have a dominant effect on the infiltration

rate, the normal opening and closing of a door in entering and leaving

a building may be small. If as a first approximation it is assumed that

the observed air leakage rate is a weighted average of the rate during

the fraction of time the door is open and the fraction of time it is

closed, it may be expressed by the relationship

t + t

o c

where ^ = infiltration rate during the time, t , when the door

is open

°

= infiltration rate during the time, t , when the door

is closed

If it is further assumed that the average duration of a door opening is

about 4 seconds, this represents about 0.1% of an hour. Thus, in terms

of the weighted average assumption the effect of a single door opening

would be less than the normal statistical variation of the infiltration

measurements. While equation 5 may underestimate the effect of intermittent door openings, empirical evidence supports the view that their

effect is usually small.

5
e. Effect of Furnace Fan on Infiltration Rate

The infiltration rates presented in Figures 5, 6, and 7 were determined with the furnace fan operating continuously in order to eliminate

fan cycling as a variable and to achieve good mixing. Comparisons were

also made between continuous fan operation and no furnace fan to determine the contribution of the fan to infiltration rate. When the furnace

fan was off, mixing was achieved with floor fans placed in the various

rooms, and an axial fan with a length of flexible duct, 1 ft (0.3 m) OD, was used to bring air from the rear bedroom to the kitchen-living area. The results of the comparison are presented in Table 4. Since this was primarily a test of the effect of the fan, the furnace was off and insideoutside temperature differences were of the order of 2 or 3 C.

Comparing the average infiltration rate with the furnace fan on and

off from the data in Table 4, an estimate of the average contribution of

the furnace fan of about 0.3 air changes per hour is obtained. This may

slightly overestimate the effect of the furnace fan, because, as noted

in the footnote to the table, the measurements were made with the grille

off of the furnace compartment allowing the fan to move more air than

normally. If the fan-off condition is compared with the results in Figures 5 and 6, an estimate of the order of 0.2 air changes per hour is

obtained

.

An important path of air leakage when the furnace fan operated was

through the airspace between the ceiling and the roof. This airspace

opened to the outside through a vent at one end of the mobile home and

opened into the furnace fan closet through an annular gap around the

chimney. Thus, it provided an almost unobstructed path from outdoors to

the furnace fan intake. When SF^ was introduced into the outside vent,

measurable concentrations appeared in the house within seconds. Thus,

the infiltration values shown in Figures 5, 6, and 7 represent the additive effect of this fan- induced leakage plus normal leakage through various cracks in the structure which is partly due to the stack effect.

Another suspected source of air leakage was through the joints in

the furnace ducts under the house. During infiltration measurements,

air samples from under the house were monitored regularly for SF^. None

was found. This suggests that furnace ducts plus the sheeting under the

house which protects them from direct exposure to the outside, were not

a major source of air leakage. It also suggests that the predominant

direction of air movement through the structure was upward even at the

small inside-outside temperature difference of 2 to 3 C.

f. Tracer Estimate of Effective Indoor Volume

In addition to use of SF^ to measure air infiltration, the tracer

gas was also used to estimate the effective inside volume of the home.

The gross inside volume of 3,600 ft^ (102 m^) noted previously was based

on floor area and ceiling height. It did not consider the volume occupied by furniture, cabinets, or any poorly accessible volumes. However,

6
by introducing a measured amount of SF^ and distributing it throughout

the house, it is possible to estimate the effective internal volume of

the house from the average initial tracer concentration. Four repetitions of this procedure on different days, using both network and supply

sampling, resulted in an estimate of 3.1 x 10^ ft^ (88 m^) as the effective internal volume of the house. The standard deviation of the measurement was slightly less than 0.3 x 10-^ ft^ (9 m^) .

g. Pressurization-Depressurization Experiments

The results of pressurization and depressurization experiments are shown in Table 5 and presented in log-log plots in Figures 8 and 9. Figure 8 also shows the effect of installing stoirm windows. There is evidence of some increase in flow resistance at higher flow rates due to the

storm windows, but the effect is small and not consistent over the entire

range. This would tend to support the observation based on tracer measurements that the installation of storm windows produced little if any

reduction in air leakage. It is to be noted in Table 5 that when flow

rates were expressed in air changes per hour, these values were much higher

than those plotted in Figures 5 and 6. An air change rate of 0.5 air

changes per hour, if achieved by depressurizing the building, would cor- respond to an extrapolated inside-outside pressure difference of the order

of 0.004 in. W.G. (1 N/m^).

The effects of pressurization and depressurization are compared in

Figure 9. It may be seen that small differences exist. The pressurization experiment showed that one of the leakage paths was around the perimeter of the structure where the base trim meets the external aluminum

wall covering. When the fan was blowing into the building, air leakage

could be felt all around the lower portion of the wall,

Strieker [1] and Tamura [2] have described fan depressurization of

homes for measuring building tightness. This technique shows promise as

a possible means of quality control of factory-built homes. As a matter

of technique, it was also observed that pressurization may have some advantage over depressurization in that steady-state conditions were reached

more rapidly when air was forced into the home. On the other hand, depressurization may be more suitable to apply in an occupied home, because

it is less intrusive to the occupants.

4 . Summary

Air infiltration measurements of a mobile home were made in an environmental chamber under controlled temperature conditions. When wind

velocity was negligible, it was found that infiltration, ^ , could be

approximated by the relationship:

& = 0.362 + 0.00586 (T^ " T^) » ^ = 0-069

7
where T-j^ and Tq are inside and outside temperatures, respectively, and

o is the standard deviation.

When fans were directed against the house, the approximation was:

^ = 0.579 + 0.00298 (T^ ~ » ^ " 0.080

The foregoing estimates were made with the furnace fan in continuous operation. In separate experiments it was estimated that furnace fan

operation contributed about 0.2 air changes per hour on the average. An

important leakage path was an annular gap around the chimney which linked

the ventilated airspace above the ceiling to the furnace fan intake.

Installation of storm windows did not have an appreciable effect on

air infiltration rate as determined by tracer measurement.

Pressurization-depressurization experiments were made in which the

pressure difference between the inside and outside was measured with a Hook gage while air was forced into or out of the house with a fan. This

test also showed that the effect of storm windows was small. When air was forced into the house, noticeable leakage was observed all around the

perimeter of the structure where the base trim meets the external aluminum wall covering. Pressurization-depressurization measurements may have

value for quality control of factory-built housing.

5. Metrication

English and metric units have been used in this report. For purposes of interconversion, some appropriate factors are given:

feet (ft) x 0.3048 = meters (m)

2 2 square feet (ft ) x 0.0929A = square meters (m )

3 3 cubic feet (ft ) x 0.02832 = cubic meters (m )

miles per hour (mi/hr) x 26.82 = meters per minute (m/min)

3 inches of water (in. W.G.) x 249.1 = Newtons per square meter (N/m )

6. Acknowledgment

This work is part of a work effort sponsored by FEA to provide base

data for developing energy conservation requirements for mobile homes.

The authors are indebted to Mr. DeWitt R. Showalter for his valuable

assistance in setting up some of the apparatus used in the measurements.

8
7. References

[1] Strieker, Saul, "Measurement of Air Tightness of Houses", Preprint

No. 2336, ASHRA.E Transactions, Vol. 81, Part 1, pp. 148-167 (1975).

[2] Tamura, G. T., "Measurement of Air Leakage Characteristics of House

Enclosures", Preprint No. 2339, ASHRAE Transactions, Vol. 81, Part

1, pp. 202-211 (1975).

[3] Hunt, C. M. , and Treado, S. J., "A Prototype Semi-Automated System

for Measuring Air Infiltration in Buildings Using Sulfur Hexafluoride as a Tracer", National Bureau of Standards Tech. Note 898,

(March 1976).

[4] Hunt, C. M. , and Burch, D. M. , "Air Infiltration Measurements in a Four-Bedroom Townhouse Using Sulfur Hexafluoride as a Tracer Gas",

Preprint No. 2338, ASHRAE Transactions, Vol. 81, Part 1, pp. 186-

201, (1975).

9
Table 1 Infiltration Rate of Mobile Home Under Conditions

of Negligible Wind Velocity

Average

T - T

1 o °C

A.l October 16

4.5 October 4

5.5 October 16

5.6 October 4

19.7 September 20

21.8 October 10

22.5 October 10

30.0 September 24

30.0 September 24

34.4 September 25

39.0 September 27

39.5 September 24

Brief door openings during

Infiltration Rate

Air Changes Per Hour

Network Supply

Run Sampling Sampling

1 0.40 0.40

1 .52 .50

2 .38^ .38^

2 .34 .30

1 .44 .44

1 .49 .52

2 .39 .42

1 .49 .49

2 .59 .60

1 .57

1 .70 .70

4 .53 .53

e measurements.

10
Table 2 Infiltration Rate of Mobile Home With External Fans

Simulating Wind Load

Average

T - T

i o

A. 5 October 15

5.1 October 15

21.5 October 9

21.9 October 9

22.4 October 9

22.7 October 9

Brief door openings during

Infiltration Rate

Air Changes Per Hour

Network Supply

Run Sampling Sampling

1 0.65^ 0.61^

2 .56 .54

1 .82 .75

4 .56 .56

3 .58 .60

2 .65^ .65^

these measurements.

11
Table 3 Infiltration Rate of a Mobile Home With Storm Windows Installed

Average

Infiltration Rate

Air Changes Per Hour

T - T

i o Run

Network

Sampling

Supply

Sampling

22.7

23.1

38.3

38.8

October 24 1

October 24 2

September 27 2

September 27 3

0.66'

.63'

.64'

.57

0.67'

.63'

.64

.52

Outside fans on, storm windows and doors sealed.

Outside fans off, storm windows and doors not sealed.

12
Table 4 Effect of Furnace Fan Operation on Infiltration Rate

Infiltration Rate

Air Changes Per Hour

Furnace Fan On Furnace Fan Off

0.19

0.64 .19

.46 .17

.47 .24

.59 .13

.48

.40 .19

average 0.51 0.19

a = 0.09 a = 0.04

The grille over the fan compartment was removed to make wiring

changes and was off during these measurements. This allowed

the fan to move more air than normally.

13
Table 5 Flow Rate as a Function of Inside-Outside Pressure

Differences for Mobile Home

Inside-Outside

Flow Rate Pressure Difference Air Changes

(cfm) (in. W.G.) Per Hour^

Inside Pressure Negative, 380 0.054 7.4

Storm Windows In n-7c o c 445 .075 8.6

530 .091 10.3

620 .117 12.0

650^ .115 12.6

840^ .175 16.3

Inside Pressure Negative, 310 0.050 6.0

Windows Out

5 3

560 .087 10.8

622 .097 12.0

635^ .102 12.3

830^ .148 16.1

Inside Pressure Positive, 180 0.025 3.5

Storm Windows In 3gg ^3

582 .099 11.3

600^ .104 11.6

800^ .142 15.5

0-=

3

; 3,100 ft (88 m-^) is an estimate of the "effective" indoor

' volume of the mobile home based on tracer

dilution measurements,

^ These flow rates measured with 7- inch (17.8 cm) orifice plate. All others

measured with 6-inch (15.2 cm) orifice plate.

14
® THERMOCOUPLE

@ NETWORK SAMPLING POINT

® SUPPLY SAMPLING POINT

^

HOT AIR REGISTER

STORM

DOOR

KITCHEN

FRONT

DOOR

SCALE

I FT

LIVING ROOM

Figure 1 Floor Plan of Mobile Home

15



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S 1,500

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400

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STORM WINDOWS OUT

- STORM WINDOWS IN

J I I I I II 1_J \ I I I I I I .015 .02.025 .03 . 04.05 .06.07 .08.09.10 .15 .25 .3 .5 .6 .7 .8 .9 IP INSIDE-OUTSIDE PRESSURE DIFFERENCE-(in.W.G.)

Figure 8 Effect of Storm Windows on Mechanically Induced Air Leakage

Pressure in Mobile I'ome Negative

22
1

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9;000

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7,000

6,000

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- INSIDE PRESSURE NEGATIVE

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Figure 9 Comparison of Air Leakage Induced by Positive or Negative

Pressurization of Mobile Hor^e

23
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. public;ation or ri-;port no. NBSIR 76-10632. Gov't Acces.sion No.3. Rccipicnt'.s Acces.sion No.

4. TITLE AND SUBTITLE

Air Leakage Measurements In a Mobile Home

5. Publication Date July 1976

6. Performing Organization (^ode

7. AUTHOR(S)

C. M. Hunt. S. J. Treado. and B. A. Peavy

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4624140

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

The Federal Energy Administration

1200 Pennsylvania Avenue, N.W.

Washington. D.C. 20461

13. Type of Report & Period Covered

Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

Air leakage measurements were made in a mobile home using sulfur hexafluoride (SF5) as

a tracer gas. The home was located in an environmental chamber where it was possible to measure and control the temperature outside the home. The effect on infiltration rate

of a number of variables was determined. These included inside-outside temperature difference, simulated wind, installation of storm windows, opening of doors, and operation

of the furnace fan. Experiments were also performed in which a fan was sealed to an opening in the house and inside-outside pressure difference measured as the fan blew air

into or out of the structure at measured rates.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) ^^j. Infiltration measurement; air leakage measurement; mobile

home tightness; sulfur hexafluoride tracer measurement

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26

22. Price

$4.00

USCOMM-OC 29042-P74