From: "Bob Ferguson" <facomail@sover.net>

To: Gil Wood/RTP/USEPA/US@EPA

Cc: "David Menotti" <dmenotti@crowell.com>, "John Crouch" <crouch@hpba.org>

Date: 05/03/2012 09:14 AM

Subject: A Comparison of Particulate Emission Rates from the In-Home Use of Certified Wood Stove 

Models with U.S. EPA Certification Emission Values (by Dr. James Houck)

Hi Gil,

Attached to this email is the study by Dr. Houck that we have mentioned and discussed in general terms 

on several recent occasions. This study is sometimes referred to as “Houck2,” to distinguish it from 

another study done by Jim (Houck1) that looks at the number of uncertified woodstoves that are still in 

the inventory. You already have Houck1.

The main focus of Houck 2 is an evaluation of whether certification test scores predict field 

performance, by comparing certification test scores with field performance data for a number of stove 

models where both data are available. Field performance was evaluated using studies conducted in 

homes with the AWES sampler and the VPI sampler, and studies conducted by VPI in the laboratory, 

using methods other than Method 28 that were developed to simulate typical consumer use practices. 

Jim validated 409 data points of field performance data -- a robust database by any definition. The 

conclusions from the study are that certification test scores do not correlate with field performance, 

with rank orders changing significantly. Sometimes models with lower certification scores had higher 

emissions in the field than models that had higher certification test scores, and vice versa. Jim also 

grouped models by certification test score categories, in an attempt to “smooth” the data. That analysis 

reinforced the conclusion, with the “Low” emissions category (<3 g/hr) performing more poorly in the 

field than the “High” emissions category (>5 g/hr). 

Jim also evaluated field performance data on uncertified stoves, concluding, as expected, that certified 

stoves have substantially lower emissions in the field than uncontrolled stoves.

This study provides another compelling reason in support of not lowering the performance standards for 

woodstoves below Washington State levels -- we simply cannot be confident that standards at lower 

levels would produce comparable emission reductions in the field. As shown by the Curkeet/Ferguson 

precision study, we also can’t be confident that there is a significant difference in performance even in 

the laboratory between a model that performs, for example, at 4 g/hr, and one that performs at 2.5 

g/hr. And, as EPA has already concluded, a further lowering of the performance standards can’t be 

justified on cost effectiveness grounds. Finally, as shown in Houck1, there are still about 6 million 

uncontrolled woodstoves in the field, with at least 4 million in regular use, more than twenty years after 

the promulgation of Subpart AAA. Houck 1 also concludes that 86% of woodstove particulates (135,000 

tons per year) are from uncertified models. 

The overall conclusion from all of this is clear and obvious: the important objective from the standpoint 

of improving air quality is changing-out the uncontrolled woodstoves. It makes no sense to lower 

performance standards if that lowering can’t be measured reliably in the laboratory, produces no 

predictable real world performance improvements, would not be cost effective, and would only slow 

down the change-out rate by decreasing the number of available models and increasing the costs of 

most of the models that would be available. 
Please let me know if you have any questions about this study. HPBA would be happy to arrange a 

conference call with Dr. Houck to address them. 

Best regards.

Bob Ferguson 

(For HPBA)

Robert W. Ferguson

Ferguson, Andors & Company

P.O. Box 678

South Royalton, VT 05068

Voice: 802-763-2339

Fax: 802-419-3799

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Wood Stove In Home v. Certification Emissions 

(Houck 2).pdf