MEMORANDUM 

DATE: October 19, 2010 

SUBJECT: Impacts of Prohibiting the Use of Conventional Spray Guns in the Wood 

Furniture Manufacturing Operations Source Category 

FROM: Kaye Whitfield, EPA/OAQPS/SPPD/NRCG 

TO: Docket No.: EPA-HQ-OAR-2010-0786 

The purpose of this memo is to document the impacts of eliminating the use of conventional 

spray guns by the Wood Furniture National Emission Standards for Hazardous Air Pollutants 

(NESHAP). 

When the rule was promulgated, conventional guns were used extensively. Since promulgation, 

the use of conventional guns in the wood furniture industry has diminished drastically, and they 

are now rarely used. Conventional spray guns have lower transfer efficiencies and higher 

emissions than other spray gun types. We believe that air assisted airless spray guns, which have 

higher transfer efficiencies, can be used in all cases where conventional air spray guns were once 

used. 

Costs

The cost of no longer using conventional air spray guns is believed to be minimal. First, the 

expected life of a conventional spray gun is estimated to be one and one-half to two years1, at the 

longest. Therefore, conventional air spray guns in use today should reach the end of their useful 

life before the compliance date for the proposed revised standard. 

Second, we anticipate no changes in coating formulation will be needed to use air assisted airless 

(AA) spray guns rather than conventional spray guns. Therefore, there will be no cost change 

related to coating usage. 

Third, the cost of an AA spray gun is estimated to be about $300 more than a conventional air 

spray gun2,3, where the cost of a conventional air spray gun is about $200.00 on average, and the 
cost of an AA gun is about $500.00 on average. This is a small cost difference, compared with 

the potential coating savings by switching to a higher efficiency spray gun. We estimate that the 

cost savings of using less coating over the lifetime of the guns will exceed the $300 difference in 

price between the two types of guns. 

Transfer efficiency is defined as the ratio of the mass of coating solids deposited on a surface to 

the total mass of coating sprayed, expressed as a percentage. Air assisted airless spray guns can 

have transfer efficiencies as high as 65% and as low as 50%.4,5 Conventional air spray guns can 

have transfer efficiencies as high as 45% and as low as 35% 4,5. 

The following equations are taken from Reference 4 but the calculations are also supported by 

References 6, 7 and 8.5,6,7,8 As shown in Equation 1, the transfer efficiency of a coating is 

proportional to the mass of coating solids that are deposited on the wood furniture part and is 

inversely proportional to the mass of coating solids that is sprayed. 

Equation 1

where: 

TE = transfer efficiency (%) 

P = mass of coating solids deposited (g solids) 

F = volume of coating sprayed (mL) 

d = density of coating (g/mL) 

S = weight percent solids of coating 

The higher transfer efficiency of AA spray guns results in lower coating use, as transfer 

efficiency is proportional to the amount of coating solids that are deposited on a wood furniture 

component. 

The amount of coating sprayed is inversely proportional to the transfer efficiency of the gun. To 

get one unit of solids on the part, a conventional spray gun (using the maximum transfer 

efficiency of 45%) needs to use 2.22 gallons of coating. To get one unit of solids on the part, an 

AA spray gun (using the minimum transfer efficiency of 50%) needs to use only 2.0 gallons of 

coating. This increased transfer efficiency represents a 9.9 percent decrease in coating 

consumption. 

For either type of gun, the annual costs are equal to the sum of the cost of the spray gun and the 

cost of coatings. The cost of coatings is equal to the product of the cost per volume of coating, 

the volume of coating used, and the number of days. 
These costs can be represented by Equations 2 and 3. 

 Equation 2

 Equation 3

where: 

CC = annual costs for conventional air spray gun 

$200 = cost of conventional air spray gun 

VC = volume of coating used by conventional air spray gun (gal) 

P = price of coatings 

CAA = annual costs for AA spray gun 

$500 = cost of AA spray gun 

VAA = volume of coating used by AA spray gun (gal) 

As shown in Equation 4, the costs of the two spray guns are equal when Equation 2 equals 

Equation 3. 

        Equation 4

As demonstrated above, there is a 9.9 percent decrease in coating usage when switching from a 

conventional air spray gun to an AA spray gun. This is demonstrated by Equation 5. 

 Equation 5

Using Equation 5, Equation 4 can be represented as Equation 6. 

 Equation 6 

With further simplification, Equation 6 becomes Equation 7 and then Equation 8. 

 Equation 7 

 Equation 8

Assuming that the typical wood furniture facility operates 4 days per week and 50 weeks per 

year, the typical year contains 200 days. If the typical cost of wood furniture coating is $25 per 

gallon, the $300 cost difference between the conventional spray gun and the AA spray gun will 

be recovered according to Equation 9. 
 Equation 9

Complete cost recovery will occur when the AA spray gun is used at a rate of 1.36 gallons of 

coating per day for a year (at a coating cost of $10 per gallon). If the cost of the coating is 

higher, the cost recovery will occur in less than a year. 

Emissions

In addition to the reduction in costs, there would also be a reduction in HAP emissions by 

switching to an AA spray gun. 

As shown in Equation 10, the volatile emissions from a coating per unit mass of coating solids 

deposited are proportional to the volume of coating sprayed and inversely proportional to the 

mass of coating solids that are deposited on the wood furniture part. 

Equation 10

where: 

E = emissions of volatile coating components (g/g solids applied) 

VC = volatile content of the coating (g/L coating) 

C = volume of coating sprayed (L) 

P = mass of coating solids deposited (g) 

The volume of coating sprayed in Equation 1 is the same as the volume of coating sprayed in 

Equation 10, except for the units. As shown in Equation 11, the volume of coating in liters in 

Equation 10 is 1,000 times smaller than the volume of coating in milliliters in Equation 1. 

 Equation 11

 where: 

 C = volume of coating sprayed (L) 

 F = volume of coating sprayed (mL) 

 1,000 = conversion factor (1,000 mL/L) 
By combining Equations 1, 10, and 11, the amount of volatiles per unit mass coating solids 

applied that are emitted when a coating is sprayed can be shown as Equation 12. 

 

 Equation 12

where: 

E = emissions (g volatiles/g solids applied) 

VC = volatile content of the coating (g volatiles/L coating) 

C = volume of coating sprayed (L coating) 

1,000 = conversion factor (mL coating/L coating) 

TE = transfer efficiency (%) 

d = density of coating (g coating/mL coating) 

S = weight percent solids of coating (%) 

With further simplification, Equation 12 becomes Equation 13. Volatile emissions per unit mass 

coating solids applied from a sprayed coating are inversely proportional to the transfer efficiency 

of the spray gun used to apply the coating. 

 

Equation 13

where: 

E = emissions (g volatiles/g solids applied) 

VC = volatile content of the coating (g volatiles/L coating) 

d = density of coating (g coating/mL) 

S = weight percent solids of coating 

TE = transfer efficiency (%) 
Equation 14

 

Equation 15

Equation 16 

The same coating is being used in both cases, so all the coating related variables cancel out, 

resulting in Equation 9.

Equation 17 

Equation 18 

where: 

Econv = emissions from the conventional gun (g volatiles/g solids applied) 

EAA = emissions from AA gun (g volatiles/g solids applied) 

VC = volatile content of the coating (g volatiles/L coating) 

d = density of coating (g coating/mL) 

S = weight percent solids of coating 

TEconv = transfer efficiency (%) 

TEAA = transfer efficiency (%) 

As shown by Equation 18, the emissions from the AA gun are 0.9 times the emissions from the 

conventional air spray gun. For every ten tons of HAP emissions from a conventional air spray 

gun, the AA gun only emits 9 tons. 

Conclusion

Prohibiting the use of conventional air spray guns will result in cost savings and HAP reductions.
References 

1. Personal Conversation. Mr. Paul Masters. Owner, Spray Gun Repair Inc.,.Thompson, 

Connecticut. November 16, 2010. 

2. Spray Gun World. 

http://www.spraygunworld.com/products/Asturo/2700/Index%202700Siphon.html. 

Accessed September 27, 2010. 

3. Spray Gun World. 

http://www.spraygunworld.com/Information2/AAA/CAT%20Gun%20Only.html. 

Accessed September 27, 2010. 

4. Spray Gun World. 

http://www.spraygunworld.com/Information2/Overspray/OversprayStart.html. Accessed 

October 24, 2010. 

5. Pacific Northwest Pollution Prevention Research Center. Transfer Efficiency and VOC 

Emissions of Spray Gun and Coating Technologies in Wood Finishing. Seattle, WA: PPRC, 

1992. http://www.p2pays.org/ref/01/00636.pdf Accessed August 10, 2010. 

6. Environmental Technology Verification Coatings and Coating Equipment Program (ETV 

CCEP): ANEST IWATA Corporation LPH 400-LV HVLP Spray Gun – Testing and 

Quality Assurance Project Plan (TQAPP), September 2003, 

http://www.epa.gov/nrmrl/std/etv/pubs/06_vr_lph400.pdf 

7. Environmental Technology Verification Coatings and Coating Equipment Program (ETV 

CCEP): HVLP Coating Equipment – Generic Testing and Quality Assurance Protocol, 

Revision 1, December 1999, http://www.epa.gov/etv/pdfs/vp/06_vp_hvlp.pdf. 

8. Environmental Technology Verification Coatings and Coating Equipment Program (ETV 

CCEP): High Transfer Efficiency Spray Equipment – Generic Verification Protocol, 

Revision 0, September 30, 2006, http://www.epa.gov/nrmrl/std/etv/pubs/600etv07016.pdf. 
Attachment 1. Price Quote for Conventional Spray Gun 

From reference: 

http://www.spraygunworld.com/products/Asturo/2700/Index%202700Siphon.html

Model 77 Siphon Feed Spray Gun 

Conventional: Compare to Binks 2001 / 2100 

Less parts - Superior Spray Pattern - Compact, light weight and balanced. 

Specially designed grip improves operator control 

and handling comfort. 

Max working pressure 90psi

SUPER SALE: Free Shipping (continenal US) No 2nd day air (call): $158.00 

Select Size s-8188^op2^2700

Amazing Features: 

Setups 

65 SS(1.5mm)

66 SS(2.0mm)

Pressure Series for Industrial Materials - Glues Indutrial Coatings. 

Stainless Steel Tips and Needles 

Siphon Pot Included 
Attachment 2. Price Quote for Air Assisted Airless Spray Guns

From reference: http://www.spraygunworld.com/Information2/AAA/CAT%20Gun%20Only.htmlAAA GUNS ONLY BELOW BOBCAT/ COUGAR / AUTOMATICSStandard Setup Waterbase Setup Solvent Base / You Can Do Water Or can be upgraded Waterbase H20 Here Water Base & Solvent Base - Yes! 

Bobcat Compact Handle Gun Your Cost: ON SPECIAL! Free Shipping $468.00Tip Set Size - Recommended shown - More below (call) 

Select Size

(All Variable fans goes down uptoapprox 3" i.e. a 10" can go from 7" to 10") 

s-8188^op2^Gun

H2O Bobcat Compact HandlYour Cost: ON SPECIAL! Free Shipping $488.00 *extra tips on special with puTip Set Size - Recommended below (call) 

Select Size

(All Variable fans goes down a 10" can go from 7" to 10") 

s-8188^
Attachment 3. Transfer Efficiencies of Conventional and Air Assisted Airless 

Spray Guns

From the following reference: 

http://www.spraygunworld.com/Information2/Overspray/OversprayStart.html