Page 1 of 9 

Final Report 

EPA Wood Heater Emission Test Method 

Comparison Study 

Prepared by Robert Ferguson 

Ferguson, Andors & Company 

For the Hearth, Patio and Barbecue Association 

December 1, 2010 
Page 2 of 9 

Background

During the Regulatory Negotiation (RegNeg) that resulted in the Wood Heater New 

Source Performance Standard (NSPS) in 1988, the data that was available to determine 

Best Demonstrated Technology (BDT) and the resultant passing grades was from the 

Oregon DEQ wood heater certification program. That data had been collected using 

Oregon Method 7, a method that was based on the traditional EPA Method 5 with its 

origins in industrial stack sampling. Since the NSPS passing grades were set using these 

data, this method became the “reference method” for the NSPS. The method, re-titled as 

Method 5H in the NSPS, sampled in the heater stack and includes a heated filter and a 

series of cooled glass impingers as the way to collect the particulate matter exiting the 

wood heater. Work had been underway leading up to and during the RegNeg on a 

different method for measuring particulates. This method involved collecting the smoke 

from the wood heater chimney in a hood and mixing it with a fairly large amount of 

ambient dilution air before drawing the particulate sample. The RegNeg committee felt 

that this method had advantages over Method 5H and it was included as an alternative to 

Method 5H. This “dilution tunnel” method was designated Method 5G, and was further 

refined to include Methods 5G-1, 5G-2 and 5G-3. Method 5G-1 uses one filter train with 

two large (100 mm) filters (primary and back-up) to collect the particulate sample. 

Method 5G-3 uses two filter trains each with of two smaller (47mm) filters and requires a 

certain precision level between trains to have a valid test. Method 5G-2 uses the Method 

5H train (heated filter and cooled glass impingers) but with the sample taken from the 

dilution tunnel rather than the heater stack. 

However, since the versions of Method 5G (5G-1 and 5G-3) that prescribed collecting the 

particulate sample on unheated filters (without impingers) were typically collecting less 

total particulate than the methods (5H and 5G-2) that included both a filter and cooled 

impingers, an equation was developed to “adjust” Method 5G-1 and 5G-3 data to Method 

5H equivalents so that the data could be used to determine NSPS compliance. 

To develop the equivalency equation, data sets were considered that included test runs 

using both test methods simultaneously. The data that was available did not define a 

clear relationship between the methods. Using “engineering judgment”, EPA proposed 

that the “best fit” to this data set was a non-linear curve, which resulted in an exponential 

conversion equation. In retrospect, it has become apparent that the test method 

correlation issue and the potential impacts for the future were not given adequate 

consideration by the RegNeg Committee. 

The current equation per EPA Method 28 is: E5Hequiv = 1.82 x E5GMeas

0.83

One problem is that the data that was used to determine the correlation between the 

methods was gathered from either conventional wood heaters or wood heaters certified 

by the Oregon program. The emission rates were generally quite high, especially when 

compared with today’s wood heaters. Also, examination of the data shows significant 

differences in the test method relationships between the different laboratories that 

generated the data. Finally, there is a logic gap in the formulation of the current equation. 

The equation imposes the highest conversion penalty, as a percentage of the measured 
Page 3 of 9 

emissions, at the lowest emission range. We have to assume that as wood heaters 

achieve lower and lower PM 2.5 emission rates, the volatile materials (those that would 

be caught in the method 5H impinger train) are being combusted rather than being 

emitted to the atmosphere. So, in theory, as total particulate emissions are reduced, the 

two methods should get closer and closer to the same result, ultimately converging at 

zero. However, the Method 28 conversion equation, perversely, operates in the opposite 

direction; as wood heaters get cleaner and cleaner, the current 5G – 5H conversion 

equation yields 5H equivalent values that increase in magnitude, with the highest 

percentage-based penalty at the lowest emission rates. 

Implications for BDT determinations in revising the NSPS 

A. Wood heater Database 

Some manufacturers recognized the impact of the present adjustment equation on their 

product emission ratings and have opted to test for certification using Method 5H or 5G2, thus avoiding the adjustment issue all together. Models that have been tested using 

Methods 5G-1 and 5G-3 were certified using converted values, which because of the flaw 

in the equation, has probably overstated their actual emission rates. 

With the upcoming NSPS revisions, EPA has tentatively agreed to have only one test 

method, rather than the two plus variations currently allowed. That method is expected to 

be ASTM E2515, a reformulation of EPA Method 5G-3. Moreover, the adjustment 

equation will be eliminated; there will be no need for it since the reference method will 

be the dilution tunnel with dual filter trains (ASTM E2515). This is universally 

considered to be a good idea. 

The enhanced EPA certified heater database currently has usable data for 147 heater 

models (including certified pellet heaters). Looking only at catalytic and non-catalytic 

wood heaters, for those models that reported what test method was used, 49 heaters used 

5H or 5G-2 and 52 used 5G-1 or 5G-3. This is shown graphically in Chart 1. 

B. Impact on BDT Determinations 

EPA must do a comprehensive analysis of data from the currently certified wood heater 

models to determine BDT and ultimately any new passing grade or grades. Since 

currently certified wood heaters have been tested using either Method 5G or Method 5H, 

the data must be all evaluated for purposes of the BDT analysis as 5G data or 5G 

equivalents. 

For heaters tested with dilution tunnel/filters only methods (Method 5G-1 or 5G-3), either 

the raw emission values can be used or the adjusted data can be converted back by 

reversing the adjustment equation. 

The real issue is what to do with the 5H/5G-2 data sets. In these cases, “dilution tunnel/ 

filter only” data do not exist so using raw data is not an option. To preserve these data 

sets (representing almost half of the available data for wood heaters) the test results will 

have to be adjusted downward to 5G-3 equivalents using another methodology. Since the 
Page 4 of 9 

current adjustment equation is now widely regarded as being grossly unrepresentative of 

the relationship between the two test methods, especially in the lower emission ranges 

typical of current heater technology, its use for conversion of the 5H data is not 

appropriate or defendable. The upcoming BDT determination, and therefore future 

passing grades, could be unfairly biased low if we are not able to establish a method 

conversion equation that is more representative at low emission rates. This impact could 

be very significant based on the large percentage of 5H (or 5G-2) tested heaters in the 

database. 

Recent Data Gathering

In cooperation with EPA (both OAQPS and OECA) HPBA funded an emission test 

method comparison program. The test method comparison testing was piggy-backed 

onto EPA certification testing with OECA allowing the comparison data (data from the 

second test method) to be excluded from the heater certification application. The testing 

was conducted between May and November, 2010 with three laboratories participating. 

Seven total heater models were tested and the models included both non-catalytic and 

pellet models. No catalytic heaters were available for testing. The participating 

laboratories provided HPBA with masked data sets showing the direct comparison 

between methods for each of the test runs conducted (including other relevant 

information about the heater and test conditions). A total of 31 individual test run 

comprise the resultant database. 

Because the test program relied on testing that was being scheduled by manufacturers at 

random rather than as part of a specifically designed test program, the resultant test data 

included three permutations of data comparison. These were 5G-3 versus 5G-2, 5G-3 

versus 5H and 5G-1 versus 5G-2. This three-way dispersion of datasets has made 

analysis of the data more complicated than was anticipated when test program was 

initially conceived. 

Table 1 presents the final method comparison data. 

Data Analysis

The purpose of this data gathering effort was to try to define a more justifiable 

relationship between the 5H/5G-2 and 5G-1/5G-3 emission measurement methods as a 

way to preserve the usefulness of the 5H/5G-2 datasets in the certified heater database. 

Although the data that was gathered may be viewed as less than ideal for its intended 

purpose, at least from a statistical perspective, it does give at least a qualitative look at the 

test method relationships with all their inherent variability imbedded in the dispersion of 

the results. 

After considering the options for treatment of the data, the conclusion that was reached 

was that the best way to consider the data was in aggregate. This approach groups the 

5G-1 and 5G-3 data together and compares it to the corresponding 5H or 5G-2 data. 
Page 5 of 9 

Table 2 shows the aggregated datasets. 

The datasets are plotted in Chart 2. The data are further identified on this chart by the 

test method comparison groupings. A linear regression line with a y-intercept = 0 is 

shown on the chart using all the aggregated data points. The slope of this line is 1.116. It 

might be tempting to eliminate some of the data from the analysis. For example, the 5G3 versus 5H data show a possible systematic difference between the methods in the two 

test series that included 5H testing (see Heaters B and C in Table 1). However, as 

pointed out in the test method variability paper presented to EPA in October, Method 5H 

has significant inherent variability due primarily to stack flow measurement and 

calculation procedure disconnects and this recently collected method comparison data 

may simply reflect the predictable variability including both random and systematic 

elements. Since there is no technical justification for disregarding any of the datasets, all 

data points were used in the regression. 

The correlation coefficient (R) is 0.9 for this regression line. This value infers a 

relatively strong relationship between the data. Although the resultant R2

 (coefficient of 

determination) value at 0.82 (82%) could be viewed as being lower than might otherwise 

be desired, it does indicate that the regression formula is a fairly good predictor of the 

overall method relationship. For the purposes of conversion of the 5H/5G-2 datasets to 

their 5G-3 equivalents, and recognizing that the overall variability in the test methods 

themselves affects both the data in this database and to an even higher degree the data in 

the heater certification database, the following formula can be used with reasonable 

confidence when converting from 5H or 5G-2 emissions to 5G-3 equivalents. 

E5G3equiv = E5H/1.116 

 
Page 6 of 9 

Chart 1 – Certification Test Method Distribution 

Cat, Non-Cat & Pellet Heaters, All QC'd Data - Methods 5G1/5G3 vs. Method 5H/5G2 Data

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 65

Ranking

M28 Weighted Ave. Emission Rate - g/hr

5G1/5G3

5H/5G2

Method 5G1/5G3

Cats. = 9, NC = 43, Pellet = 14

Method 5H/5G2

Cats. = 6, NC = 43, Pellet = 3

Data 1/25/10

3/23/10

Cat Non-Cat

Non-Cat Pellet
Page 7 of 9 

Table 1 – Final Emission Test Method Comparison Data 
Page 8 of 9 

Table 2 – Aggregated Data 
Page 9 of 9 

Chart 2 – Emission Test Method Comparison Emission Test Method Comparison Data y = 1.1163x

R2 = 0.818

9.08.07.06.05.04.03.02.01.00.0

14.013.012.011.010.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0

EPA Method 5G1 or 5G3 Emission Rate (Unadjusted) - g/hr

EPA Method 5G2 or 5H Emission Rate - g/hr All 5G1/3 v. All 5G2/5H 5G3 v. 5G2 5G3 v. 5H

5G1 v. 5G2Linear (All 5G1/3 v. All 5G2/5H)

11/29/10