### Rebuttal To: “Evaluation of Method 28 Wood Heater Burn Rates ” Prepared by James E. Houck, Jeremy Clark, and Thomas Christensen OMNI Environmental Services, Inc. Dated September 21, 2009

This rebuttal prepared for : Gil Wood , Staff Lead for Re sidential Wood Heater NSPS United States Environmental Protection Agency

Prepared by
Thomas P. Morrissey Woodstock Soapstone Company, Inc., 66 Airpark Road, West Lebanon, NH  03768

‐ and

‐ Harold Garabedian Energy & Environmental Analytics, 132 Nor thfield St., Montpelier, VT  05602

November 2 , 2012

### 1 In September 2009 , a report commissioned and paid for by the Hearth, Patio, &
Barbecue Association (hereafter HPBA) and entitled “Evaluation of Method 28 Wood Heater Burn Rates” (her eafter the “Houck Paper”) was published by OMNI Environmental Services, Inc.
and subsequently presented to EPA. The Houck Paper suggests a rational e for increasing the Low Burn Rate required by Method 28, or reducing the weighting applied to the Low Burn Rate,

or both

. Rai s ing the low burn rate requirement would be advantageous to stoves that do not burn cleanly at low outputs 1

. The Houck Paper has been referenced repeatedly by some manufacturers, and by HPBA , as evidence that burn rates used i n Method 28 should be increased.  However, the conclusions
of the Houck Paper are not supported by the data it cites

. The Houck Paper focused almost exclusively on (1) the “endpoint” determinat ions for certification tests conducted under Method 28 (hereafter “Method 28 Tests”), and (2) the “endpoint” for in

‐ situ tests using the automated woodstove emission sampler (AWES)
conduc t ed in Vermont, New York , and Oregon (hereafter “In

‐ Situ Tests”) whic h were used to determine burn rates and weighting in the original NSPS.  The Houck paper makes “hypothetical” calculations based on the assumption that “AWES and METHOD 28 conditions were directly comparable,” which they are not, as explained below.

The t wo respective “endpoint” conditions are as follows:

Method 28 Test Endpoint:
Method 28 Tests for EPA Certification are conducted in a laboratory setting with the appliance on a large scale. Following the Method 28 Test protocol , a “pre

‐ burn” is conducted under prescribed conditions prior to each test , and a coal

‐ bed of a specified weight is required to be developed.  After the coal

‐ bed is developed, the scale is reset to zero (0.00 kgs) and the
test fuel is loaded.  Whe n the test fuel has been completely consumed and the scale again
reaches 0.00 kg, the Method 28 Test endpoint has been reached. Th us, the end of the test
occurs when is all the fuel has been consumed , and the burn rate is defined as the weight of fuel

c onsumed divided by the time elapsed to consume that fu e l. The weight of the coal

‐ bed is not

1 A database prepared by HPBA in 2009 showed that of 110 “non

‐ catalyt ic” stoves still in production, the average emissions was 3.88 g/hr at low burn (Category 1), vs. 3.45 g/hr at Category 2; 2.99 at Category 3; and 4.43 at Category 4 .  Any (a) increase in the low burn rate or (b) decrease in the weighting of low burns woul d boost the test results of these stoves.  The recently proposed ASTM Test M e thod would achieve both of these goals.

### 2 included in the calculation. A majority of Method 28 Tests typically last between 2 and 8 hours, though some are shorter or longer.

In

­ Situ Test “Endpoint”:
The In

‐ Situ Tests were 7

‐ day in

‐ home studies, conducted with an automated woodstove emission sampler (AWES).  Since an In

‐ Situ Test stove could not be placed on a scale, the fuel was weighed separately before it was loaded.    The Houck Paper states that

“T he endpoint of a “burn” was determined to be when the temperature dropped to below 100 degrees F in t he chimney connector at the one

‐ foot monitoring point.” 2

However this “ endpoint ” definition was not actually used in the definition of the dataset

. The 100oF marker was simply used to indicate that the stove was no longer in use, and to inform the AWES sampler to stop collecting emissions.
In

‐ Situ Tests were conducted over a one

‐ week period, and ended at the e nd of seven days.  The AWES stop ped collecting data when and if the stack temperature at 12 inches above the flue outlet dropped below 100 degrees , a s noted above. The vast maj ority of In

‐ Situ Tests
ended with temperatures well above 100 degrees, since the end of the test was determined by time (7 days) and not flue temperature.  In some of the 7

‐ day In

‐ Situ tests, the woodstove being sampled never reached the 100

‐ degree flue te mperature.  In other tests the woodstove reached
the 100

‐ degree flue temperature in the early morning or late afternoon because the stove was not capable of sustaining a fire until the resident awoke in the morning and re ‐ loaded the stove ,
o r returned from work to re

‐ load the stove before the fire went out .  In other cases, the
woodstove reached the 100

‐ degree temperature and stayed at that temperature for 8

‐ 10 hours (while the resident was away or otherwise chose not to operate the stove).
The In

‐ Situ Tests were conducted over one week periods, with sampling interruptions only when the stack temperature at 12” declined below 100 degrees.  The In

‐ Situ Testing encompassed over 18, 5 00 hours of data .  Ther e were approximately 18,588 hours of woodstove operation in the In

‐ Situ Testing, and approximately 240 occasions when the stove being tested
reached a 100 degree flue temperature.  In most cases where the stove reached 100 degrees, it was immediately refueled. The average uninterrupted test period between these 100o events was approximately 77.45 hours (18,588 total hours/240 one hundred degree occasions = 77.45

2 Houck Paper, page 1

### 3 hours average).  The period of time consumed by the cooling of the stack to 100 degrees wa s a small percentage of the total time : no more than 5

‐ 6%.

Test Duration:  In

­ Situ Tests vs

. Method 28 Tests The average test duration of the In

‐ Situ Tests was approximately 77.45 hours. The Houck Paper compares th es e In

‐ Situ Tests to forty six Method 28 Tests that lasted an average of 3.65 hours, or 4.7% of the length of an average In

‐ Situ Test. This is a critical difference in the
data sets and a difference not addressed in the Hou ck paper. The Houck Paper then posits that a) since it “hypothetically” took the In

‐ Situ Test stoves
about six hours to cool down to the 100 degree mark, then b) this six hour “cool down” time should be added to the Method 28 Tests (average length 3 .65 hours) in order to c) get a real comparison of burn rates in the In

‐ Situ Tests and the Method 28 Tests. This mathematical
contrivance ( reconciling unrelated and dissimilar “endpoints” by mathematically addin g long
cool

‐ down time s to Method 28 Tests) has the effect of 1) producing test times that are on average 3 times longer ( the average test time in his fo rty six Certification Tests is 3.65 hours 3 ; the average test time in his “adjusted” tests is 9.5 hours 4 ) and produces “Hypothetical 100 oF Burn Rates (Kg/h)” that are all approximately 0.5 kg/hr 5 (as opposed to an average of  1. 50 in the forty six Certification Tests) .  In fact , the Houck Paper concludes; “The average hypothetical burn rate (had the Method 28 endpoint been a one

‐ foot stack temperature of less than 100oF) is more than 3 times lower than the burn rate
calculated f rom the Method 28 endpoint.” 6 This would be truly entertaining if it hadn’t been repeated ly advanced as justification for raising
the burn rates in the Method 28 Tests.

The Houck Paper Argument: Here is the argument put forth by the Houck Paper : 1. Since th ere is an apparent discrepancy between the Method 28 Test endpoint and the
In

‐ Situ Test “endpoint”;
2. And since the (a) determination of Method 28 burn rates and (b) determination of weighting for these burn rates relied on the In

‐ Situ Testing ;

3 This is the average of 46 Total Test Times in Table 1, pp 6

‐ 7 of the Houck Paper
4 See Table 3 , pg 9, C olumn entitled “Time to 100oF ” in the Houck Paper)
5 See Houck Paper, Table 3, page 9, last column
6 Houck Paper, page 4

### 4 3. Then, if the two “endpoints” are directly comparable, the Method 28 Tests should “hypothetically” be extended until the stack temperature at 12 inches above the flue
reached 100 degrees ( when the coal

‐ bed would be largely consumed).
4. Further, since this would generate a burn rate well below what was targeted by the In

‐ Situ Tests and identified by the NSPS as “representative”, then the Method 28 Burn
Rates should be increased

. 5. This supports the HPBA position that Low Burn Rates and M edium B urn R ates for the Method 28 Test should be increased, and their weighting decreased.

Why the Houck Paper is Misleading : The Houck Paper is incomplete, inaccurate , and misleading for the following reasons:

a. The Method 28 and In

‐ Situ Test “endpoints” are not comparable because the test
duration of the in

‐ situ testing was one week (168 hours), and the average test time between 100 degree flue temperatures was approximately 77 hours whereas the average Method 28 tests presented in the Houck Paper was 3.65 hours;
b. The Method 28 Test and In

‐ Situ Test “endpoints” are not comparable because the time spent cooling down to the 100 degree flue temperature i n the In

‐ Situ Tests was a very small percentage of the total test time (5

‐ 6%), whereas when this time
i s “hypothetically” attached to the end of a Method 28 Test it becomes a very large percentage of the test time (over 50%);

c. The Houck Paper states that the “raw data” from the In

‐ S itu testing is unavailable, but graphs of each 7 day test showing  “Stove Te mperature, Flue Oxygen, Fueling
Practices and Heati ng System Use” are available on the EPA Web Site in a study entitled “Performance Monitoring of Advanced Technology Woodstoves:  Field Testing for Fuel Savings, Creosote Build

‐ up and Emissions”. 7 The rea son why the availability of data is important is that any person with a modicum of curiosity could go to the EPA website and confirm the data for himself/herself. To discount the accuracy, usefulness and weighting of the Method 28 protocol based on
the fac t that AWES Sampling and Method 28 Test Sampling have different “endpoints” is error. The Houck Paper misrepresents the data for the benefit of its paying client, HPBA, which seeks

7 For graphs of each 7day in

‐ situ study, see Appendix D, pp D1

‐ 115 in Volume II of “Performance Monitoring of Advanced Technology Wood Stoves:  Field Testing for Fuel Savings, Creosote Build

‐ Up and Emissions ”, prepared for New York State Energy Research and Development A uthority by Omni Environmen tal Services, November 1987, and readily available as a pdf on the EPA web site.

### 5 an increase in Burn Rates defined by Method 28 Tests.  The data simply doesn’t support the “hypothetical calculations” proposed in the Houck Paper.



### FURTHER DISCUSSION It is helpful to remember that the Houck Paper compares endpoints of forty six Method
28 Tests where the Test Time ranged from 1.17 hours to 7.83 hours, and the average was 3.65 hours, to the 113 In Situ Tests where the Test Time ranged from 84 hours to 168 hours; the average Test Time was 163.57 hours, and the average time between “endpoints” was 77.45 hours, or an average of 21.2 tim es the length of the Method 28 Tests in question.  See Table 1

. Table 1 # of Shortest Longest Average Total tests Test Time Test Time Test Time Test Hours 9/21/09 Houck Paper 46 1.17 hours 7.83 hours 3.65 hours 168.1

AWES I n - Situ Tests 113 84 hours 168 hours 163.57hours** 18,588 **Overall average for In

- Situ Tests was 163.57 hours. Average time between 100o "endpoints" for In

- Situ Tests: 77.45 hours Below is a sample of an In

‐ Situ Test with no “endpoints”:  the stove ran for seven days
and never reached 100 oF.

Other In Situ Tests reached the 100o F point several times in a one

‐ week test period. For example, the stove graphed below dropped to the 100 degree “endpoint” three times in the
first half of the one week test, each time at approximately 6:00 AM when the stove ran out of fuel and needed to be reloaded.  The last 3.5 days have no such occurrences.

### 6 The Houck Paper would have a credulous reader believe that every Method 28 Test should have a long “cool down endpoint” attached to it to be consistent with the original In

‐ Situ Testing.  To get an idea of what this would mean, imagine adding the tail on the graph below (in blue) to the Method 28 Test ( a sample Method 28 Test is superimposed below, in red).  Note the obvious difference in scale (5.5 hours for the Method 28 Test (in red) vs. 168 hours for the In

‐ Situ Test).

### 7 If the Houck Paper were correct, and the “endpoints” really were comparable, and the “endpoints” really did occur at similar frequencies, t hen each In

­ Situ Test would be an endless series of endpoints , which of course they are not. Therefore the 100 O F criterion is not a meaningful definition of an endpoint : as a practical matter it was infrequently attained, and the endpoint of these tests was defined as occurring at the end of a one week interval.



### ADDITIONAL IN

­ SITU STUDIES
A decade after the in

‐ situ testing in Vermont, New York, and Oregon, add itional in

‐ situ testing was performed in Klamath Falls and Portland, OR, using the same AWES monitoring system, with test periods running for 7 days (for a summary, see APPENDIX A, pp 9

‐ 10 ). The Klamath Falls study included 2,881 hours of data col lection with an average burn
rate of 0.98 kg/hr. The stoves installed in Portland were run for 2,509 hours at an average
burn rate of 1.19 kg/hr .  Summaries of the In

‐ Situ Tests results from Klamath Falls and Portland are printed on pages 9

‐ 10 . If an ything , these results merely confirm the accuracy of the original study of stoves in Vermont, New York, and Oregon, which was used to determine weighted burn rates for the original NSPS.
Burn rates in the 1987

‐ 88 in

‐ situ studies in Vermont, New York, and Oregon  showed
that 50 percent of measured burn rates were less than 1.2 kg/hr

. 8 The committee negotiating the original NSPS agreed that the frequency distribution developed from the in

‐ home studies reasonably represented the full range of actual consume r wood use. No subsequent study has invalidated this original finding ;  to the contrary, later tests confirmed it.
The original committee negotiating NSPS also noted that some heaters “could easily be modified by the consumer either by removing damper sto ps or through the use of a stack damper to achieve longer burn times, and thereby create high emissions.” 9 Consumer advertising is additional evidence that burn rates around 1.00 kg/hr are intended throughout the industry.   A review of stove advertising shows that most stoves with
fireboxes between 1.8 and 3.0 cubic feet advertise burn times between 10 and 22 hours.  These burn times, advertised by manufacturers and expected by consumers, cannot be reasonably attained without operating the stoves at low b urn rates, exactly as the In

‐ Situ Tests confirm.

8 Federal Register, Vol. 52, No. 32, Page 5002 , February 18, 1987 9 Federal Register, Vol. 52, No. 32, Page 5002, February 18, 1987

### 8 SUMMARY

Method 28 defines burn rate in a very straightforward way

– you build a bed of coals, you add fuel, you measure the time it takes to consume that fuel and divide the weight of fuel charged by the t ime it takes to consume that fuel. The Houck paper considers an alternative endpoint , contrived from In

‐ Situ Testing

. To compensate for the difference between the Method 28 Test endpoint and the contrived In

‐ Situ “endpoint” , the Houck Paper suggests adding a hypothetical long “cool

‐ down tail” to comparatively short Method 28 tests, and then recalibrating burn rate s and weighting .  This is error, because it ignores (1) the duration of the
In

‐ Situ Tests (168 hours); (2) the infrequency of “100 degree endpoints” in the In

‐ Situ Testing (on average once every 77.45 hours); and (3) the small percent of the overall In

‐ Sit u Test time occupied by these so

‐ called “endpoints (approximately 6%). In summary, there is nothing in the Houck Paper to suggest that burn rates determined for the original NSPS were too low, or weighted too heavily.  Subsequent In

‐ Situ Tests and indust ry advertising also confirm that the original burn rates and weighting were correctly determined.

### 9 APPENDIX A Summary of 1998

‐ 99 Klamath Falls, OR stoves using AWES Sampling Equipment 2, 881 total hours; average burn rate 0.98 Kg/hr; Avera ge Stack Temp 443 o.

### 10 Summary of 1998

‐ 99 Portland , OR stoves using AWES Sampling Equipment 2,509 total hours; average burn rate 1.19 Kg/hr; Average Stack Temp 371o.