Document ID: EPA-HQ-OAR-2009-0734-0011
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2014-02-03T05:00Z

April 7, 2010

Gil Wood

4930 Old Page Road

Room E140, MC-143-02

Durham, NC 27709

Dear Gil,

I have been ask by the Catalytic Hearth Coalition (CHC) to provide you
with information regarding the efficiency of catalytic cordwood stoves
in respect to efficiency related programs such as the Energy Star Label
and the Home Star Program, as well as, efficiency considerations that
may be part of a new NSPS.  Simply put, as a group, catalytic cordwood
stoves (and inserts) are more efficient than their non-catalytic
counterparts.  As you know, this has been recognized for some time as
manifested in the default efficiency values of 72% for catalytic
woodstoves as compared to 63% for non-catalytic woodstoves in the
current NSPS [40 CFR §60.536 (i)(3)].

I would like to call your attention to three new bodies of research that
have further documented the benefit of catalyst technology, both in the
terms of efficiency and particulate emissions.  These are:  1. A
catalyst longevity study conducted by OMNI for the CHC.  2. A
survey/review of burn rates and particulate emissions rates of certified
wood heaters conducted by Ferguson, Andors & Company for the Hearth,
Patio and Barbecue Association (HPBA) with additional data reduction
done by OMNI.  3. A review of U.S. socio-demographic and climate data
conducted by OMNI that illustrates the prevalence of burning conditions
under which catalyst heaters are expected to outperform non-catalytic
models.  A brief summary of the findings of each study is provided here.
 More detailed information can be provided at your request.

Catalyst Longevity

Catalyst longevity in the earliest woodstove models was believed to be
short (on the order of five years) and was the basis for promulgating a
lower particulate standard (4.1 g/h) for catalytic stoves as compare to
that for non-catalytic stoves (7.5 g/h).  The rationale for the lower
catalytic stove standard was that as the catalyst degraded with time the
emissions would increase and, on the average, over the lifetime of the
appliance, the emissions would be similar between catalytic and
non-catalytic woodstoves.  It is the contention of the CHC that well
designed modern catalytic woodstoves “protect” the catalyst from
thermal stress and direct flame impingement and that catalyst longevity
is not an issue.  OMNI measured emissions from two woodstove models with
used catalysts removed from residences.  Only a very modest
deterioration in particulate emissions was seen in the older catalysts
(eight and nine years old for the two stove models, respectively) as
compared to new catalysts.  While limited in number, OMNI’s tests
suggest that catalyst degradation in a well designed stove, within
reason, is not an issue.

Low Burn Rate Performance

Ferguson, Andors & Company working with the HPBA attempted to obtain
individual burn rate and corresponding emission rate data for all
currently manufactured certified wood heaters.  Data for many stove
models were successfully obtained.  OMNI calculated emission factors
(g/kg) from these data as 

emission factors are a better indicator of the completeness of
combustion than emission rates.  While not a definitive indicator, lower
emission factors would tend to correlate with higher combustion
efficiencies.  Overall thermal efficiency is the product of combustion
efficiency multiplied by thermal efficiency.  Consequently, if all else
were equal, stoves with lower emission factors would tend to have higher
efficiencies.  As expected, the mean emission factors for catalytic
stoves were lower than for non-catalytic stoves at all burn rate
categories specified by the Method 28 test procedure.  Notably, the mean
emission factors for catalytic stoves were much lower than for
non-catalytic stoves at the lower burn rate categories suggesting a
disproportionally better performance of catalytic stoves than
non-catalytic stoves at lower burn rates.

Low Burn Rate Occurrence and Cold Starts

As noted, catalytic stoves appear to operate disproportionally better at
lower burn rates than non-catalytic stoves.  Review of surveys conducted
by the Energy Information Administration (EIA), American Housing Survey
(AHS), Simmons Marketing Research, and HPBA reveals that:  (1) 22% of
housing units with occupants reporting using a woodstove are in the
lowest heating degree day category (<4000 HDD).  (2) 24% to 32%
(depending on the survey) of housing units with occupants reporting
owning or using a woodstove are in the South census region.  (3) 45% of
woodstove fires are reported as occurring during non-winter months
(spring, summer, or fall).  While burn rates in the lowest category are
not the most common scenario, they are likely to occur a significant
fraction of the time, particularly in milder climates and during the
margins of the heating season.  The burn rate distribution developed for
the current NSPS does not take milder climates or the margins of the
heating season into consideration.

It is believed that catalytic stoves achieve their emission reduction
potential sooner than non-catalytic stoves after the start of a fire
because only the catalyst needs to be brought up to temperature not a
large mass of metal and firebrick in the area of secondary combustion
needed for emission reduction and high efficiency with a non-catalytic
stove.  Review of EIA and HPBA surveys reveals that at a minimum 42% to
52% of woodstove fires begin with a cold start.  The current NSPS
testing procedure (Method 28) uses a hot start only.

Summary

As a group, catalytic stoves have higher efficiencies and lower
particulate emissions than non-catalytic stoves.  Their efficiencies are
disproportionately higher and their particulate emissions are
disproportionately lower than non-catalytic stoves at lower burn rates
and with fires that begin with cold starts.  Neither low burn rates nor
cold starts are adequately addressed in the current NSPS.  Catalyst
longevity does not appear to be an issue with well designed stoves.

Gil, if you have any questions or need more information please do not
hesitate to contact me.

Sincerely,

James E. Houck, Ph.D.

President

cc:  Larry Brockman

       John Ackerly 

 Services, Inc.

Consulting ( Engineering ( Testing

www.omni-environmental.com

Mailing:	Post Office Box 301367 ( 97294				Phone:	(503) 643-3788

Street:	13327 NE Airport Way   					Fax:	(503) 643-3799

	Portland, Oregon ( 97230 ( USA				Email:	houck@omni-test.com