1

Summary of Discussion and Action Items from 

10/21/2010 HPBA-EPA Wood Stove NSPS Meeting

Date of Meeting: October 21, 2010

Time: 8:30 am – 11:30 am

Purpose: The purpose of the meeting was for HPBA to present information to EPA on test 

methods and other topics for consideration in its deliberation of possible revisions to propose 

to the wood heater NSPS (40CFR Part 60, Subpart AAA). HPBA provided presentations to help 

guide the discussion. The agenda of topics was 1) Test Method Variability; 2) Method

Comparison; 3) Pellet Ash; 4) Economics; and 5) PFI (Pellet Fuels Institute). Powerpoint 

presentations and handouts provided by HPBA are attached to the summary.

Participants: 

Allan Cagnoli, HPBA

John Crouch, HPBA

Rick Curkeet, Intertek

Daniel Henry, Hearth and Home Technologies

Bob Ferguson, HPBA

David Menotti, Crowell & Moring for HPBA

Amanda Aldridge (on phone), EPA

Larry Brockman, EPA

David Cole, EPA

Chebryll Edwards, EPA

Greg Green, EPA

Larry Sorrels, EPA

Mike Toney, EPA

Gil Wood, EPA

Graham Fitzsimons, EC/R

Bill Huang, EC/R

Introduction

• Allan Cagnoli opened by saying that HPBA has spent a lot of time, money and effort to 

collect and provide information to EPA.

• Greg Green emphasized that just because EPA proposes something, it does not mean it 

will be finalized and that EPA has not made up its mind yet on final rule revisions.

• David Menotti added that HBPA’s efforts were designed to generate robust facts.
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Test Method Variability - Rick Curkeet presented a Powerpoint and HPBA provided a paper on 

Test Method Variability. The Powerpoint slides are shown in Attachment 1, and the paper is 

provided in Attachment 6. Questions and comments regarding this presentation are 

summarized below.

• HPBA described the elements of precision: repeatability, which answers whether a lab

can repeat with similar results; and reproducibility, which answers whether different 

labs can get similar results.

o The primary data set available to evaluate test result variability is that generated 

through the EPA required Accredited Laboratory Proficiency Test Program. 

o It is apparent that the repeatability and reproducibility of the test procedures are 

not very good. 

o Even without applying any statistical tools, one can simply look at the results of 

testing the same stove in the same laboratory over two or more years to see the 

range of intra-laboratory results. 

o Using the results from all the laboratories for all the stoves over all the years of 

the program, it is possible to assess the inter-laboratory precision.

o Using 2.8 times the standard deviation to estimate the potential range of results 

that could be expected with a 95% confidence level [Ref.: ASTM E177, 28.1], it is 

clear that the for any given test series the reproducibility is on the order of ± 4.9 

– 9.8 grams per hour. This means that for any emissions rate measured using 

the EPA test methods, the result could be 4.9 to 9.8 grams per hour higher or 

lower if the appliance were tested again at a different laboratory. 

 Gil Wood asked if this was relative to the mean or a percent basis.

 Rick Curkeet also stated that the translatability to real world conditions is 

also an issue here.

o Gil Wood also asked that as devices improve over time, won’t variability 

decrease? 

• A key question HBPA sought to answer in their study is: Where is the variability coming 

from?

o Is it method related or does it arise from a different source- that is, a variable 

performance of the appliance itself.

 To answer this, they started with emissions measurement methods (5G1, 5G-2, etc.) and then addressed the operation side, Method 28. They

concluded that the emission measurement methods only explained a 

small part of the overall variability shown by the precision analyses.

o Using the EPA proficiency test data, it is possible to examine several of the 

various Method 28 parameters for their impact on precision, including:
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 Impacts of burn rate variations. The high burn rate variability is 

substantial, and it is certain that this variability is a contributing factor in 

the emissions variability. However, Rick Curkeet said that fact that you 

don’t get the same burn rate at the same operating conditions is 

significant; therefore, burn rate variability does not explain much of the 

overall variability of emissions rates.

 Impacts of fuel moisture variation and fuel density variation. Rick 

Curkeet stated that by looking at the chart, it is clear that there is no 

relationship. Gil Wood stated that John Kinsey believes moisture content 

is important. He also pointed out that this wasn’t done with non-catalytic 

stoves. There is a difference between talking about moisture content 

variability allowed by the method (as opposed to the real world).

o Bob Ferguson said that although intuitively tightening method (e.g. moisture 

content) should improve results, the data is not there to support this. Tightening 

these parameters to improve test precision would simply increase costs and the 

data show that such tightening would not significantly improve precision.

o Mike Toney asked if lab temperatures were looked at.

 Rick Curkeet responded yes, and as well as barometric pressure too, but

the impacts can’t be quantified. Bob Ferguson noted that it was an “eye 

opener” how these can impact results from the same product.

o Their conclusion (as stated in their paper), is that variability in wood heater 

emission testing results for any given appliance is most likely a function of the 

random nature of burning wood, no matter how tightly you try to control the 

process. Many relatively small, uncontrollable variables that are inherent in the 

wood combustion process can combine to significantly affect the outcome of any 

given test.

 Larry Brockman emphasized the importance of educating on how to burn 

properly, and the group agreed.

• Gil Wood said that 85% of stoves sold meet the WA state standard.

o Rick Curkeet stated that the target is now 4.5 gr/hr for non-cat units.

 Maybe they improve the unit to get it or just get lucky.

• Gil Wood was interested to know how many test runs were there before certification 

run.

• David Menotti said that the WA standard took the NSPS compliance margin away.

o What the study showed is that there is no real difference between a 2 and a 4 

gr/hr. 

• Rick Curkeet said he would rather test Cat 2 burn rate 5 times and report the average 

rather than look for the lowest number.
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• Dan Henry said that nobody has worked harder to product clean stoves than Quadrafire.

o The economy has caused them to look for a different market channel. They 

found it and none of it is certified (because of loopholes and exemptions). Gil 

Wood stated that EPA is looking at closing certification loopholes.

o Quadrafire has developed two new “eco choice” pellet stoves that are EPA 

certified at 3 gr/hr, and predicts sales of 20,000 – 30,000 units/year.

Update on Test Method Comparison - Bob Ferguson provided a presentation for the group. 

His Powerpoint slides are shown in Attachment 2. Questions and comments regarding this 

presentation are summarized below.

• The issue involving the long suspected flaw in the equation used to “adjust” the 

emission values determined using EPA Methods 5G-1 and 5G-3 to EPA Method 5H 

equivalents was outlined in a report dated March 30, 2010.

o Bob Ferguson said that all points in the report were sent to Gil back in April.

• Bob Ferguson is still doing QA on data and will provide more when he has it, but, so far 

it looks like the cleaner you get, the more you are penalized under the current 

correction equation. (e.g. 7 corrects to 9, 0.7 corrects to 1.5)

o Dan Henry said this is why Quadrafire used 5H to certify, even at an extra cost.

o Allan Cagnoli pointed out that the cost to HPBA is an issue, and that this would 

double the cost of each run.

o HPBA said that paying for correction is too much, and getting data is problematic 

because of time and money.

o David Menotti asked if EPA wanted HPBA to keep submitting data (and is there 

time to submit data?)

o Gil Wood said he would have to think about it.

o Bob Ferguson said that one lab had asked not to do anymore. Bob said 5H 

requires additional technology. It’s taken months to get the data.

Impact on Pellet Ash - Bob Ferguson provided a presentation on Pellet Fuel Ash. His 

Powerpoint slides are shown in Attachment 3. Questions and comments regarding this 

presentation are summarized below.

• Dan Henry explained that every pellet stove tested has probably used low-ash douglasfir from the Pacific NW, however, pellets that are most commonly available in other 

areas of the country where pellet heaters are popular are made from hardwood have a 

higher ash content.
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• Though there is limited data (more is coming), there appears to be a trend between 

higher ash fuels and higher particulate emissions.

o HPBA state that there was almost no data directly comparing low and high ash 

wood pellet fuels in the same heater using the same test method.

o Bob Ferguson stated that there is one softwood versus hardwood pellet test 

series that has been completed, still needs to be QA’d.

• There was concern over the impacts of BDT since different pellets might produce 

different results, even when the burn settings are optimized.

o HPBA stated that if this is a BDT list, it could mean hardwood pellet 

manufacturing may not be able to stay in business.

• Dan Henry made a point that all pellets on the Test Results page were lean burners.

Economics Impacts of NSPS “Straw man” Proposals on Hearth Product Companies - David 

Menotti provided the presentation. His Powerpoint slides are shown in Attachment 4. 

Questions and comments regarding this presentation are summarized below.

• David Menotti recounted that the current NSPS had a massive and largely unanticipated 

impact on woodstove manufacturers. It has led to a decrease in the number of 

manufacturers (about 400 to 60)

o HPBA emphasized that it is in everyone’s interest to avoid repeating that 

experience this time around.

• HPBA has therefore taken steps to develop high quality economic impact data for 

consideration by EPA. 

o They hired NERA, a top-flight economic consulting firm to assist, because NERA is

allowed a broader reach. John Crouch noted that some foreign owned 

companies (e.g., Napoleon and Yodel) are players and the Canadians are critical.

• NERA developed guidance for manufacturers in preparing economic impact 

assessments.

o The NERA guidance was given to SERs in the SBREFA process for their use in 

preparing their presentations to the SBREFA panel.

o HPBA identified a group of manufacturers that are broadly representative of our 

membership.

 These companies have agreed to perform analyses of the impacts on 

their businesses of the "straw man" proposals provided to the SBREFA 

panel, using the NERA guidance.

o The SBREFA submittal will come as CBI (pushing for October 31).

o By early next week, Larry Sorrels will get with John Crouch and maybe NERA to 

discuss the process/questions.
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Status Report on PFI - John Crouch led the presentation and provided handouts (included as 

Attachment 5). Questions and comments regarding this presentation are summarized below.

• John Crouch said the letter containing the PFI fuel grade requirements was drafted in 

response to Gil’s comment.

• John Crouch said that there are many mills that will have difficulty holding to 1% ash.

• Gil Wood said he appreciated what PFI has done here.

Action Items/Next Steps

• Gil Wood and Mike Toney to get back to Bob Ferguson on 5G-5H. Bob Ferguson would 

like to get on a call with Gil Wood and Mike Toney in the future to discuss a plan if they 

could get more data points.

• By early next week, Larry Sorrels will get with John Crouch and maybe NERA to discuss 

the process/questions.

• Overall Schedule from Gil Wood

o Proposal in June

o SBREFA panel report is next (EPA is a little late on this)

 SBA/OMB/EPA will have differences that proposal will address

o “Early Guidance” Meeting with AAS this coming Tuesday (Oct. 26, 2010)

o Options selection in December

o Draft preamble in January or February

o Trade Show in 1st week in March, will be attended by Gil Wood or David Cole, 

who will give an update.

o Mike Toney is going to spring ASTM Meeting.
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Attachment 1

EPA Wood Heater Test Method Variability Study Analysis of Uncertainty, Repeatability and 

Reproducibility based on the EPA Accredited Laboratory Proficiency Test Database
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Slide 1

1

EPA Wood Heater Test Method Variability Study

Analysis of Uncertainty, Repeatability and 

Reproducibility based on the EPA Accredited 

Laboratory Proficiency Test Database

Rick Curkeet, PE

Chief Engineer – Hearth Products

Intertek Testing Services

Robert Ferguson

Ferguson, Andors & Company
3

Slide 2

2

Introduction

• The precision of any test method is an extremely 

important tool in understanding the limitations of 

the data generated from the method.

• No rigorous assessment of the precision of the 

test methods contained in the woodstove NSPS 

has ever been performed.

• A large data base of proficiency test data from 

accredited laboratories has been assembled.

• The objective of this paper is to perform that 

assessment, using the EPA proficiency test data 

base and broadly accepted tools for assessing 

repeatability and reproducibility.
4

Slide 3

3

EPA Test Methods

•EPA Method 28 – Certification and Auditing of Wood Heaters

•EPA Method 5H – Determination of Particulate Matter Emissions from 

Wood Heaters from a Stack Location

•EPA Method 5G-1 - Determination of Particulate Matter Emissions 

from Wood Heaters (Dilution Tunnel Sampling Location), Single Filter 

Train with Dual 100mm Filters (filters at near ambient temperature)

•EPA Method 5G-2 - Determination of Particulate Matter Emissions 

from Wood Heaters (Dilution Tunnel Sampling Location), Method 5H 

Filter Train (heated front filter with chilled impinger train)

•EPA Method 5G-3 - Determination of Particulate Matter Emissions 

from Wood Heaters (Dilution Tunnel Sampling Location), Dual Filter 

Trains with Dual 47 mm Filters (filters at near ambient temperature)
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Slide 4

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• All measurement processes have an inherent 

element of variability in the measurement result.

• Each measurement that is made as part of the 

test procedure, and ultimately combined 

mathematically to produce a result, contributes 

to the overall uncertainty of that result. The 

more measurements made, the greater the 

overall uncertainty. 

• This variability can be evaluated empirically by 

performing multiple measurements of a single 

artifact and evaluating the mean and standard 

deviation of the test results. 

Test Method Variability
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Slide 5

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• The relative magnitude of the standard deviation 

to the mean is a measure of the dispersion 

(variability) of the measurement process. 

• This measure of dispersion includes variability 

that originates both from the measurement 

processes and from the inherent variability of the 

phenomenon being measured. 

• When the measurement involves performance of 

a process which might be affected by 

uncontrolled variables or by the ranges allowed 

for operational parameters within the process, 

the variability associated with the process is 

usually much greater than that that arises from 

the uncertainty of the actual measurements 

made. 
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Slide 6

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The NORMAL Distribution

NORMAL DISTRIBUTION

-4 -3 -2 -1 0 1 2 3 4

STANDARD DEVIATIONS

95%

MEAN

68%
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Slide 7

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Terminology

• The closeness of agreement between independent test 

results obtained under stipulated conditions is the 

“precision” of the measurement. 

• Precision is usually broken down further into:

– Repeatability – The closeness of multiple measurements of the 

same artifact under the same conditions with the same 

equipment and operator. The symbol “r” is often used to refer to 

repeatability. Repeatability can be evaluated by replicate tests of 

the same product at the same laboratory following the defined 

procedure.

– Reproducibility – The closeness of measurements made on the 

same or presumed to be identical artifacts by different 

laboratories, equipment and operators. The symbol “R” is often 

used for reproducibility. Reproducibility can be evaluated for any 

quantitative measurement system through an Interlaboratory 

Study or round robin test program.
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Slide 8

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Quantifying Test Method Precision

• The primary data set available to evaluate 

test result variability is that generated 

through the EPA required Accredited 

Laboratory Proficiency Test Program. 

– A total of 14 laboratories have participated 

over the years (to varying degrees).

– 5 individual test heaters have been used in 

the proficiency test program.
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Slide 9

9
11

Slide 10

10

• This database can be analyzed using 

standard statistical tools.

• This database can be further analyzed 

using advanced statistical procedures 

specifically intended to assess test method 

variability (ASTM E691).
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Slide 11

11

“Macro” Analysis Using Standard Statistical Tools
13

Slide 12

12

• Since there is a wide range in the weighted 

average emissions performance for each stove 

in the database, both the standard deviation and 

the coefficient of variation (CV) were computed 

for each stove to avoid any potentially 

misleading assessments of variability that might 

result from the wide range in the calculated 

means for the individual test stoves. 

– Note: The coefficient of variation represents the ratio 

of the standard deviation to the mean, and it is a 

useful statistic for comparing the degree of variation 

from one data series to another, even if the means 

are drastically different from each other. 
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Slide 13

13

• It is apparent that the repeatability and 

reproducibility of the test procedures are 

not very good. 

• Even without applying any statistical tools, 

one can simply look at the results of 

testing the same stove in the same 

laboratory over two or more years to see 

the range of intra-laboratory results. 
15

Slide 14

14

• Using the results from all the laboratories 

for all the stoves over all the years of the 

program, it is possible to assess the interlaboratory precision.

– Using 2.8 times the standard deviation to 

estimate the potential range of results that 

could be expected with a 95% confidence 

level [Ref.: ASTM E177, 28.1], it is clear that 

the for any given test series the reproducibility 

is on the order of ± 4.9 – 9.8 grams per hour. 
16

Slide 15

15

• This means that for any emissions rate 

measured using the EPA test methods, 

the result could be 4.9 to 9.8 grams per 

hour higher or lower if the appliance were 

tested again at a different laboratory. 

• Even at one standard deviation (68% 

confidence level), the reproducibility 

interval is about 1.7 to 3.5 grams per hour, 

i.e., there is a 32% chance that a new test 

result would deviate by more than this 

amount. 
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Slide 16

16

• The CV calculations further confirm that 

variability is high (>40 % CV) for the three test 

stoves with significant data sets but it is not 

consistent for all units. 

• Since CV is calculated from one standard 

deviation, the implied variability in the actual 

data is really about 2.8 times the CV at a 95% 

confidence level. For example, a CV of 40% 

implies that the results of any one test could vary 

by +/- 112% from a population mean with a 

probability of 5% or less of being farther away.
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Slide 17

17

ASTM E177

3.1.12 repeatability limit (r), n—the value below which the 

absolute difference between two individual test results 

obtained under repeatability conditions may be expected to 

occur with a probability of approximately 0.95 (95 %).

3.1.12.1 Discussion—The repeatability limit is 2.8 (1.96 x√2 ) 

times the repeatability standard deviation. This multiplier is 

independent of the size of the interlaboratory study.

3.1.12.2 Discussion—The approximation to 0.95 is reasonably 

good (say 0.90 to 0.98) when many laboratories (30 or more) 

are involved, but is likely to be poor when fewer than eight 

laboratories are studied.
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Slide 18

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Precision Analysis Using ASTM E691

• Under the presumption of using 

consensus standards, we determined that 

ASTM E691 – Standard Practice for 

Conducting an Interlaboratory Study to 

Determine the Precision of a Test Method

was appropriate for use here. 
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Slide 19

19

• ASTM E691 provides procedures for planning 

and conducting studies of the precision of test 

methods, and also provides statistical 

techniques for performing precision analyses. 

• Since the EPA proficiency test program has 

been on-going for more than 20 years, the test 

program design components of ASTM E691 are 

not germane here. 

• However, the analytical procedures can be 

applied to the EPA proficiency test data for the 

purposes of determining precision (both r & R). 
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Slide 20

20

• Separate tables were created for each of 

the different stoves that were tested over 

the years the proficiency test program was 

conducted where there is sufficient data to 

apply the procedures specified in ASTM 

E691. 
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Slide 21

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23

Slide 22

22
24

Slide 23

23
25

Slide 24

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Conclusions from ASTM E691 Analyses

• The ASTM E691 analyses shows that the 

repeatability (within lab), r, of the weighted 

average emissions rate determined by the 

EPA test methods at the 95% confidence 

level is at best ±2.9 grams per hour and 

typically about ±3.5 to ±5.4 grams per 

hour. The reproducibility (between labs), 

R, at the 95% confidence level is ±4.5 to 

±6.4 grams per hour. 
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Slide 25

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Sources of Variability in EPA Wood 

Heater Testing

• Given that 12 labs (five are still accredited) 

and all four particulate measurement 

methods are represented, it is important to 

try to understand if the repeatability and 

reproducibility issues are laboratory and 

method related or arise from a different 

source – that is, variable performance of 

the appliance itself. 
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Slide 26

26

• To evaluate that question, we next 

investigated the potential sources of 

variability in the test methods. 

– We started with the emissions measurement 

methods (5G-1, 5G-2, 5G-3 and 5H), and 

then addressed Method 28, which specifies 

how the appliance is to be operated during 

emission testing.
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Slide 27

27

Emission Measurement Methods

Method 5G-1

• Potential sources of variability in Method 5G-1 include 

the following:

– Accuracy of dilution tunnel gas flow and sample flow 

measurement and the resulting consistency of proportionality.

– Recovery of particulates from the probe and front half of filter 

holder using a solvent cleaner.

– Weighing errors for tare and final weights of filters and 

evaporation containers used to collect and weigh the catch.

• These sources combine to produce an estimated 

measurement uncertainty of about ±2.7 to 3% of the 

emission value measured for a typical passing wood 

stove test. 
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Slide 28

28

Method 5G-2 

• Potential sources of variability in Method 5G-2 include 

the following:

– Accuracy of dilution tunnel gas flow and sample flow 

measurement and the resulting consistency of proportionality.

– Recovery of particulates from the probe and sampling line using 

a solvent cleaner.

– Recovery of particulate collected in the impingers and 

connecting glassware.

– Weighing errors for tare and final weights of filters and 

evaporation containers used to collect and weigh the catch.

• These sources combine to produce an estimated 

measurement uncertainty of about ±3 – 3.5% of the 

emission value measured for a typical passing wood 

stove test. 
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Slide 29

29

Method 5G-3

• Potential sources of variability in Method 5G-3 

include the following:

– Accuracy of dilution tunnel gas flow and sample flow 

measurement and the resulting consistency of 

proportionality. 

– Weighing errors for weights of filters, probes including 

front filter housings and filter seals.

• The measurement uncertainty of method 5G-3 

has been determined to be approximately ±

2.5% of the emission value measured for a 

typical passing wood stove test. 
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Slide 30

30

Method 5H

• Potential sources of variability in Method 5H include the 

following:

– Accuracy of flue gas flow and sample flow measurement and the 

resulting consistency of proportionality.

– Recovery of particulates from the probe and sampling line using 

a solvent cleaner.

– Recovery of particulate collected in the impingers and 

connecting glassware.

– Weighing errors for tare and final weights of filters and 

evaporation containers used to collect and weigh the catch.

• These sources combine to produce an estimated 

measurement uncertainty of about ± 20 to 30% of the 

total particulate mass determination. 

• The major contributor to MU is the difficulty in 

measurement of low and variable stack flow rates.
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Slide 31

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Conclusions Regarding the Contribution of 

Emissions Measurement Method Uncertainty to 

Overall Method Variability

• It is apparent that the emission 

measurement methods explain only a 

small part of the overall variability shown 

by the precision analyses. 

– It should be noted that Method 5G-3 showed 

lower variability in the analyses than the other 

emission measurement methods. 
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Slide 32

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Operating Protocol for the Appliance (EPA Method 28)

• Potential Sources of Variability in Method 28 include the 

following:

– Fuel density variation from approximately 30 to 40 lb/ft3 (dry 

weight basis).

– Fuel moisture content variation from 19 to 25% dry basis (varies 

in uniformity as well as average).

– Fuel load configuration details.

– Coal bed size (20-25% of fuel load weight) and pre-burn 

temperature conditions.

– Loading time and start-up procedure.

– Ambient temperature, barometric pressure and humidity.

– Variations in control settings and resulting burn rates.

– Random uncontrollable variables such as when and how the fuel 

load settles, falls and collapses.
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Slide 33

33

• Using the EPA proficiency test data, it is 

possible to examine several of the various 

Method 28 parameters for their impact on 

precision.

– Impacts of burn rate variations. 

• Emissions performance is related to burn rate to 

some degree. 

– Higher burn rates generally produce more complete 

combustion. 
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Slide 34

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• The proficiency test data does not lend 

itself well to determining the impact of burn 

rate variability over the full burn rate range 

of the heater in that each lab must adjust 

the air control(s) to a setting that will 

produce a burn rate in each of the required 

burn rate categories. 

• The exception is the high burn rate 

(Category 4) which is always run with the 

air control(s) fully open. 
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Slide 35

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37

Slide 36

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Burn Rates

• The high burn rate variability is substantial, and 

it is certain that this variability is a contributing 

factor in the emissions variability.

• There are many instances in the proficiency test 

data where two runs in one lab at very similar 

burn rates produced substantially different 

emissions rates. So burn rate variability does not 

explain much of the overall variability of 

emissions rates.
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Slide 37

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– Impacts of fuel moisture variations

– Impacts of fuel density variations

• The following charts show the relationship between 

emissions and fuel moisture content and emissions 

and load weight (assumed to relate to fuel density) 

for the 121 runs conducted on the catalytic 

proficiency test stove in 1987 and 1988. Using the 

“Corner Score” statistical test where a score of >11 

indicates potential dependency between variables 

[Ref.: Mark’s Standard Handbook for Mechanical 

Engineers, 17-22], it is clear that there is no 

relationship. 
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Slide 38

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1987 &1988 Cat Stove 1 - % M.C. v Emissions

y = -0.1496x + 7.4864

R2

 = 0.0048

0

2

4

6

8

10

12

14

16

18

20

15 17 19 21 23 25

%M.C. Dry Basis

Emssions (g/h)

Emissions Rate

Median MC

Median Emissions rate

Linear (Emissions Rate)

Corner Score +4
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Slide 39

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1987 &1988 Cat Stove 1 - Load Wt. v Emissions

y = -0.2276x + 7.368

R2

 = 0.0048

0

2

4

6

8

10

12

14

16

18

20

9 10 11 12 13 14 15 16

Load Weight (lbs)

Emissions (g/h)

Emissions Rate

Med. E

Med. Laod Wt.

Linear (Emissions

Rate)

Corner Score +2
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Slide 40

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• By practical necessity, EPA Method 28 contains 

tolerances on operational and fueling parameters. 

These include fuel density, moisture content, laboratory 

ambient temperature, coal bed size, fuel load weight and 

several others. While it might be supposed that the 

method variability could be lessened by even tighter 

specifications within the test method relating to fuel and 

operating conditions, the data does not support this 

proposition. 

• Without these tolerances or specified ranges wood 

heater emission testing would become prohibitively 

expensive with significant additional costs incurred while 

attempting to control these variables within a significantly 

narrower range than specified. As demonstrated, these 

additional costs would not significantly reduce variability.
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Slide 41

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Final Conclusions

• The repeatability and reproducibility of wood 

heater emission testing as demonstrated by the 

EPA accredited laboratory proficiency test data 

is quite poor. 

– At the 95% confidence level, repeatability for the EPA 

weighted average emission rate is at best ±2.9 g/hour 

and ranged as high as ±5.4 g/hour. 

– The reproducibility was no better than ±4.5 g/hour 

and ranged as high as ±6.4 g/hour.
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Slide 42

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Final Conclusions

Emissions r & R - Best Case

0

2

4

6

8

10

12

14

16

18

20

0.51.52.53.54.55.56.57.58.59.5

10.511.512.513.5

Mean Emissions Rate (g/h)

95% Confidence Limits

Intralab

r

Mean Emission g/hr

Interlab

R
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Slide 43

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Typical Distribution
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Slide 44

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• Further analyses of the potential sources 

of variability have shown that the emission 

measurement test methods (EPA Methods 

5G-1, 5G-2, 5G-3 and 5H) are not major 

contributors to the high overall variability 

being demonstrated by the data. 

– However, Method 5G-3 does demonstrate 

the lowest uncertainty of the four methods 

currently specified in the NSPS.
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Slide 45

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• Analyses of the variability inherent in EPA 

Method 28 also indicate that the 

operational and fuel parameter tolerance 

ranges specified in that method are not 

major contributors to the high variability. 

– Tightening these parameters to improve test 

precision would simply increase costs and the 

data show that such tightening would not 

significantly improve precision.
47

Slide 46

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• This leaves the only logical conclusion. 

– Variability in wood heater emission testing 

results for any given appliance is most likely a 

function of the random nature of burning 

wood, no matter how tightly you try to control 

the process. 

• Many relatively small, uncontrollable variables that 

are inherent in the wood combustion process can 

combine to significantly affect the outcome of any 

given test.
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Slide 47

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• These conclusions should not be taken to mean 

that the current test methodology is inadequate 

to characterize an appliance’s emissions 

performance. 

– There is no question that the currently certified low 

emissions wood stoves produce far less particulate 

emissions than their pre-regulation predecessors 

which produced emissions rates of over 50 to 100 

grams per hour. 

– Our primary conclusion is that the current testing 

process simply cannot reliably distinguish emissions 

performance differences of less than 4 to 6 grams per 

hour. The process is certainly capable of reliably 

distinguishing between good and bad performance, 

but it cannot reliably distinguish between “good, better 

and best” performance.
1

Attachment 2

Wood Heater Emission Test Method Comparison
2

Slide 1

Wood Heater Emission Test 

Method Comparison

EPA Methods 

5G-1/5G-3 versus 5G-2/5H
3

Slide 2

Background

• The issue involving the long suspected 

flaw in the equation used to “adjust” the 

emission values determined using EPA 

Methods 5G-1 and 5G-3 to EPA Method 

5H equivalents was outlined in a report 

dated March 30, 2010. This report was 

forwarded to EPA in April 2010.
4

Slide 3

• It has been widely suspected by users of the 

EPA wood heater test methods that the test 

method adjustment equation used to “correct” 

EPA Methods 5G-1 and 5G-3 to EPA Method 5H 

equivalency was flawed, especially in the critical 

lower emission range (<7.5 g/hour).

• This issue has taken on new importance with the 

evaluation of BDT using the EPA certified heater 

database.
5

Slide 4

• The subset of that database identified by HPBA 

as representing the majority of currently 

produced heaters includes nearly 50% heater 

models tested using either M5H or 5G-2.

• The importance of understanding the true 

relationship between the test methods is 

amplified if the database is to be evaluated 

using M5G-3 (ASTM E2515) as the “currency” 

for evaluating BDT. 
6

Slide 5

• Adjusting the 5H/5G-2 data to 5G-3 

equivalents using the inverse of the 

present adjustment equation could skew 

the database.

• This, in turn, impacts the BDT analysis.
7

Slide 6

Action

• HBPA worked with OAQPS and OECA to create 

a procedure that allowed a second emission 

measurement method to be run simultaneously 

with the method designated for use for 

certification testing. The second method would 

not be reported for certification purposes. 

• For example, if M5G-1 was being used for 

certification, M5G-2 was piggy-backed on to 

allow a direct comparison of the results.
8

Slide 7

• HPBA absorbed the cost of adding the 

second emission measurement method 

and has accumulated the comparison 

data.

• The data we have gathered so far is 

presented here. It should be noted that 

the M5G-1 and 5G-3 values are as 

measured (not adjusted to 5H 

equivalents).
9

Slide 8

Emission Test Method Comparison Data (through October 19, 2010
10

Slide 9

Analyses

• The data show varying relationships when 

comparing subsets of the data.

• The datasets breakdown as follow:

– M5G-3 versus M5G-2

– M5G-3 versus M5H

– M5G-1 versus M5G-2
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Slide 10
12

Slide 11

Preliminary Conclusions

• The impacts of testing at three laboratories 

with three different combinations of test 

method comparisons has resulted in a 

relatively noisy database.

• The data does indicate that the current 

adjustment equation does not reflect the 

relationship between the methods.
1

Attachment 3

The Impact of Pellet Fuel Ash Content on Particulate Emission Performance of Pellet Heaters
2

Slide 1

The Impact of Pellet Fuel Ash 

Content on Particulate Emission 

Performance of Pellet Heaters
3

Slide 2

Background

• Many of the certified pellet heaters were tested 

using pellets with very low ash content (< 0.5%). 

• These pellets are made from softwood feed 

stock and are produced in the Pacific Northwest.

• These pellets are commonly available for the lab 

that conducted much of the pellet heater 

certification testing.

• Pellets that are most commonly available in 

other areas of the country where pellet heaters 

are popular are generally hardwood or mixed 

wood and have higher ash content (>1%). 
4

Slide 3

• There was supposition that higher ash 

fuels would result in higher particulate 

emissions.

– This was based on observations made by 

pellet heater manufacturers when they tested 

other fuel types (corn, grains, hulls, etc.) that 

were known to have higher ash content than 

wood pellets.
5

Slide 4

• There was almost no data directly 

comparing low and high ash wood pellet 

fuels in the same heater using the same 

test method.

• There was concern over the impacts on 

BDT since different pellets might produce 

different results, even when the burn 

settings are optimized.
6

Slide 5

• This concern expands further when other 

fuel types are considered (corn, grain, 

hulls, pits, switch grass, etc.)
7

Slide 6

Action

• HPBA has been working to obtain data 

that will shed some light on this potential 

problem.

• Some comparison testing has been 

conducted, both in manufacturer labs and 

one EPA accredited lab.

• The results obtained to date are shown in 

the following table.
8

Slide 7

Test Results (To-date)
9

Slide 8

• There is one softwood versus hardwood 

pellet test series that has been completed 

but the data has not been QA’d. This data 

will be added will be available within a few 

days.
10

Slide 10

• An assessment of the impact on BDT 

determination must be made before pellet heater 

emission levels (passing grade(s)) can be set 

within the revised NSPS.

• The performance of pellet heaters on higher ash 

fuels can still provide a clean-burning option.

• Without considering this issue, alternative biofuel development and heater development for 

those fuels could be stifled.
11

Slide 9

Conclusions

• Based on the limited data obtained so far, it 

appears that higher ash pellets will produce 

higher levels of particulate emissions.

• Due to the fact that pellet heaters include 

combustion air blowers, it is likely that the 

additional PM collected with the higher ash fuels 

is primarily ash (inorganic) that has been 

entrained in the exhaust flow.

• The higher ash pellet fuels dominate the 

available pellet fuel supply in areas other than 

the west coast (primarily due to available 

feedstock for the pellet mills).
1

Attachment 4

Assessment of the Economic Impacts of NSPS “Strawman” Proposals on Hearth Product 

Companies
2

Slide 1

1

ASSESSMENT OF THE 

ECONOMIC IMPACTS OF NSPS 

“STRAWMAN” PROPOSALS ON 

HEARTH PRODUCT 

COMPANIES

October 21, 2010
3

Slide 2

2

• Costs and other economic impacts are an 

important input into the NSPS process.

• All stakeholders therefore have an interest 

in seeing that the record contains high 

quality data that accurately reflects the 

potential impacts of new standards on the 

hearth industry.

Background
4

Slide 3

3

• The current NSPS had a massive and 

largely unanticipated impact on woodstove 

manufacturers. It is in everyone's interest 

to avoid repeating that experience this 

time around.
5

Slide 4

4

HPBA Activities

• For these reasons, HPBA has taken steps 

to develop high quality economic impact 

data for consideration by EPA in the NSPS 

process.

– We hired NERA, a top-flight economic 

consulting firm to assist in this effort.
6

Slide 5

5

• NERA's first assignment was to prepare 

guidance for use by our manufacturers in 

preparing economic impact assessments.

– That guidance reflects and implements the 

latest EPA and OMB guidance on how to 

perform these assessments. 

– A copy of that guidance has been provided to 

EPA.
7

Slide 6

6

SBREFA

• The NERA guidance was provided to the 

SERs in the SBREFA process for their use 

in preparing their presentations to the 

SBREFA panel.
8

Slide 7

7

• HPBA identified a group of manufacturers that 

are broadly representative of our membership.

– These companies have agreed to perform analyses of 

the impacts on their businesses of the "straw man" 

proposals provided to the SBREFA panel, using the 

NERA guidance.

• In addition, HBPA has made arrangements for these 

companies to seek assistance from NERA in developing 

these analyses.

• The final products of this effort will be submitted 

by the companies to EPA, hopefully in the near 

future. 

Beyond SBREFA
9

Slide 8

8

CBI

• Much of the data in these reports will be 

CBI. The companies will submit these 

data to EPA in compliance with EPA's 

procedures for CBI submissions.
1

Attachment 5

Pellet Standards Update for EPA/OAQPS, October 21, 2010
2
3
1

Attachment 6

EPA Wood Heater Test Method Variability Study
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