# An Evaluation of Overall Efficiency for EPA

Certified Non-catalytic Wood Heaters

Prepared for the Hearth Patio and Barbecue Associat ion (HPBA)

By: Robert Ferguson

Ferguson, Andors & Company

July 21, 2011Page 2 of 6

Introduction

In order to provide a meaningful response to EPA’s recent disclosure of their intent to add overall efficiency limits (passing grades) to the p roposal for the revised New Source Performance Standard (NSPS), the Hearth, Patio & Ba rbecue Association (HPBA) has undertaken an efficiency data gathering effort. Al though EPA has indicated that they will propose that all regulated product categories will include overall efficiency allowables, this report focuses on wood heaters.

Wood heater manufacturers were asked to provide CSA B415.1-2010 overall efficiency data for their certified wood heater models, along with corr esponding EPA emissions certification values for currently produced models that meet Washington State emission limits. In some cases, the data were provided by test laboratories after recei ving permission from several manufacturers.

The efficiency results we have received represent t he only known overall efficiency database for currently certified wood heater models. Every effo rt was made to insure that a high level of data quality was achieved. However, the database is by no means perfect or complete. Many of the efficiency values were determined by using pre-exis ting data in conjunction with the new CSA B415.1-2010 efficiency calculation spreadsheet. A few of the results that were received were determined to be close surrogates and therefore usa ble for the intended purpose. For example, one company had conducted only three test runs span ning the operating range for each model rather than the usual four. The majority of the da ta were generated by EPA accredited laboratories although some of the data came from ma nufacturers’ R & D labs. In all cases, the weighted average overall efficiency was determined using the same burn rate probability weighting scheme required in EPA Method 28 when det ermining the EPA weighted average particulate emissions rate. This allows a direct comparison of emissions and overall efficiency

for the datasets.

However, it is important to note that the precision of the CSA B415.1-2010 test method, and more specifically the stack loss efficiency determi nation portion of that method, has not been

determined. And the EPA emission test methods have been previously shown to include a high level of variability 1 . Therefore, the unknown uncertainty of the effici ency test results presented here in conjunction with the emission result variab ility must be considered when drawing

conclusions from these data.

Data

Table 1 includes data from 68 non-catalytic heater models. At the request of the manufacturers as a means of protecting confidential business info rmation (CBI), the manufacturer and model identity is masked.

1 Curkeet, R. and Ferguson, R, EPA Wood Heater Test Method Variability Study - Analysis of
Uncertainty, Repeatability and Reproducibility base d on the EPA Accredited Laboratory Proficiency Test

Database, October 6, 2010.Page 3 of 6 Table 1

Overall efficiency results for seven catalytic mode ls were received. Results were in the range of 72.1% to 82.4%. The overall efficiency values for these models were determined using the 2000 version of CSA B415.1. It is expected that these v alues as reported will be within ± 1 or 2% of the values using CSA B415.1-2010.

Data Analysis

The data for non-catalytic models were evaluated in several ways. First, a frequency distribution was created. Figure 1 is a bar chart showing the d istribution of overall weighted average efficiencies by efficiency range for the 68 non-cat alytic heater models. It should be noted that ranges shown are equal to or greater than the first number and less than the second. For example, the range 65 – 70 is actually 65.0 to 69.9

.

Figure 2 is a plot of weighted average overall effi ciency versus weighted average particulate emissions for the 68 non-cat models. The purpose o f this evaluation was to see if there was any relationship between emissions performance and effi ciency. A linear regression line was fit to

the data and a corner score 2 analysis conducted.

2 Ref.: Mark’s Standard Handbook for Mechanical Engin eers, Eighth Edition, 17-22Page 4 of 6 Figure 1Page 5 of 6 Figure 2

Discussion

Although it should be noted that some of the models in this database might postdate the

enhanced EPA certified wood heater database that wa s submitted to EPA by HPBA in February, 2010, it is estimated that this database represents more than 60% of the 96 non-catalytic models with emissions of 4.5 g/hr or under included in the enhanced EPA certified wood heater database. Of the 68 non-catalytic wood heater model s in this database, 21 models have weighted average overall efficiencies that are below the pro posed level of 70%. This represents 31% of

the heater models in the database

The average of all 68 models is 71.0% with a standa rd deviation of ±3.8%. The median efficiency is 71.8%.Page 6 of 6

The weighted average emission rates for the 21 mode ls below 70% overall efficiency range from 1.2 to 4.5 g/hr with an average of 3.6 g/hr and a s tandard deviation of ±0.8 g/hr. The weighted average emission rates for the 47 models with overa ll efficiency equal to or greater than 70% range from 0.7 to 4.5 g/hr with an average of 3.0 g /hr and a standard deviation of 1.0 g/hr.

The precision of the CSA B415.1-2010 stack loss eff iciency test method has not been

determined.

The linear regression line has a very poor R 2 value indicating no relationship between particula te emission performance and overall efficiency.

The corner score test confirms there is no correlat ion or association between particulate emission performance and overall efficiency.

Too little data (n = 7) were obtained to allow any meaningful analysis for catalytic wood heaters. However, the limited data available suggest less ri sk for this category of heaters.