United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-94/193 December 1994
EPA Project Summary
Woodstove Durability Testing
Protocol
R. D. Bighouse, S. G. Barnett, J. E. Houck, and P. E. Tiegs
Woodstove field studies during seven
heating seasons have shown that new
technology woodstoves designed to
have low particulate emissions have
frequently shown rapid degradation in
emission control. This degradation has
been documented both by measure-
ment of particulate emission factors
with an in-home automated emission
sampler (AES) and by observable physi-
cal damage to the woodstove compo-
nents. Most of the damage appears to
occur when the woodstove is allowed
to operate at exceptionally high tem-
peratures. A method to test the
long-term durability of woodstove mod-
els in the laboratory in a 1- to 2-week
time frame has been developed and
has come to be referred to as a stress
test.
Two avenues of research have been
taken in developing the stress test pro-
tocol. First, the performance of
woodstoves while in actual in-home use
has been observed during two heating
seasons in three communities: Medford
and Klamath Falls, OR, and Glens Falls,
NY. Eight models of stoves in 13 homes
were studied. The field studies permit-
ted records of woodstove operating
temperatures, particulate emission lev-
els, and (in some cases) physical deg-
radation to be followed in a real world
setting. The second line of research
was the laboratory "stressing" of vari-
ous woodstove models under high tem-
perature operation. This laboratory
research has been conducted on six
stoves (five models) and, as with the
in-home research, changes in particu-
late emission rates were measured and
physical degradation documented. Both
catalytic and noncatalytic stove mod-
els, including EPA Phase 2 certified
stoves, were represented in the tests.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Recently, there has been much con-
cern by regulatory agencies and stove
manufacturers about long-term physical
degradation of woodstoves and elevated
air pollutant emissions due to this degra-
dation. In the past, such degradation could
be observed only in the field after one or
more heating seasons of use, after a par-
ticular model had been widely introduced
to the market. Consequently, improvement
in the manufacturing and design of
woodstoves in response to degradation
has been slow.
The development of an accelerated test
to simulate in-home woodstove aging and
degradation over a short period of time in
the laboratory is reported here. Because
stoves are aged under extreme conditions,
the process is termed a "stress test." The
goal of the project was to develop a proto-
col by which a woodstove could be oper-
ated in the laboratory for a short period of
time (about 1 week) to simulate one heat-
ing season in the field. The short turn-
around time has been deemed necessary
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to evaluate a stove's long-term perfor-
mance and durability so that stove design
and manufacturing can be modified while
the stove model is being developed.
Development of a Stress Test
Stress testing was done to subject tar-
get stoves to a cyclic pattern of high
temperature exposures. To maintain con-
sistency, a protocol was developed to
specify all parameters of woodstove burn-
ing, including fuel type, moisture, size,
and configuration; loading density; wood-
stove air settings; startup method; length
of time doors and bypasses are open;
stack height; and criteria for refueling.
Throughout the development of a stress
testing protocol, many of the above pa-
rameters were held constant, while others
were varied to determine the combination
of factors that would lead to the most
extreme burning condition. The param-
eters held constant were the following:
Fuel Type
Split lodgepole pine, as free of knots
as possible.
Fuel Moisture
10 to 20% (dry basis).
Fuel Length
Five-sixths of the longest firebox di-
mension.
Fuel Configuration
Fuel in center of firebox, packed tightly
with smaller fuel on bottom.
Air Settings
Stove settings set to maximize burn
rate and firebox temperatures.
Kindling Load
Maximum of 15 minutes in duration.
Length of Bypass Opening
For catalytic stoves only, bypass open
for additional 7 minutes after stove
door is closed.
Stack Draft
Minimum of 17.4 Pa (0.07 in. H2O) for
90% of the burn cycle.
Refueling
A temperature threshold was empiri-
cally determined for each stove model
by putting fuel wood loads into oper-
ating stoves. The temperature that
corresponded to the conditions when
there was first enough space (from
the burndown of the previous load) to
put the full wood load into the stove
was later used as a reloading prompt
for each stove model.
Four parameters were varied through-
out protocol development, and the effects
on temperature were analyzed:
Fuel Size
Two different fuel sizing regions were
used: (1) 70% "large," 30% "small,"
and (2) 100% "small." Wood was con-
sidered large if it fit through a 20-cm
(8-in.) diameter hole but not through
a 13-cm (5-in.) diameter hole. Wood
was considered small if it fit through
a 13-cm (5-in.) diameter hole but not
through an 8-cm (3-in.) diameter hole.
Loading Density
Loading densities used were 48, 112,
and 160 kg/m3 (3, 7, and 10 Ib/ft3) of
firebox volume.
Length of Door Openings
Stove door was left open between 3
and 45 minutes after fuel was loaded.
Stack Height
Two stack heights were used: (1) 6.1
m (20 ft) and (2) 8.2 m (27 ft).
Results
Five stoves were stress-tested using
protocol 6. Data for one stove used in the
development of the final stress test proto-
col (Blaze King Royal Heir #1) are pre-
sented in the report and represent the
effect of protocols 2 through 5. Each stove
was emissions-tested prior to stressing
and once again afterwards. Some stoves
underwent extended stress testing. The
physical degradation is summarized in
Table 1. Particulate emissions and a more
detailed description of physical degrada-
tion (in both homes and the laboratory)
are provided in the report by stove model.
Conclusions
Considerable variation in woodstove
degradation has been observed in home
usage. For some, degradation was ob-
served to be more severe than that pro-
duced by the in-laboratory stress test
protocol. For others, little in-home degra-
dation was observed even after two heat-
ing seasons. Such variability is not
surprising in light of the differences in
installation, use habits, and fuel types seen
with woodstoves. The research presented
here shows that deterioration similar to
that caused by 10 days (240 hours) of
stressing a stove following protocol 6 is a
reasonable predictor of the deterioration
that may be seen under the more extreme
in-home usage conditions after one heat-
ing season. Each of the protocol variables
has been quantified so that the protocol
can be standardized and used in a repro-
ducible manner. This protocol can be used
as a tool to estimate particulate emissions
of a population of aging stoves. It can
also be used by stove manufacturers dur-
ing the design stage to ensure that a
durable stove with low emissions over a
long period of use is produced.
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Table 1. Observations of Physical Damage Due to Stressing
Blaze
Duration King
of Royal
Stressing Heir
(days) #11
4 Some oxidation
and warpage
Blaze King
Royal Heir
#2
Country Flame
BBF-6
Regency R3/R9 Quadrafire 31 00 Earth Stove 1003C
7 Continued oxidation
and warpage
Catalyst tested;
still fully active
None
10
Bypass gap
of 0.64 cm
Baffle plate oxidized
and moderately
warped (matches Y20,
Y24)
Minor warping and
oxidation of
baffle and
secondary air
tubes
Some warping and
oxidation of
catalyst holder
14 Bypass gap of 0.64 cm
20 2 Test complete
Test Catalyst holder oxidized
complete and slightly warped
(similar toY14)
25
35
Extensive baffle
warpage
Major warping and Failure of bypass
Catalyst holder oxidized
and warped (identical to
Y14 after two seasons)
Still no bypass gap
Test complete
oxidation of
baffle and
secondary air
tubes
Test complete
mechanism
(stuck open)
Severe oxidation
and warping of
catalyst holder
Warped door frame
(not airtight)
Test complete
' Protocols 2 through 5 were used with the Blaze King Royal Heir #1; all others used protocol 6.
2 Observation after 18 days of stressing for the Regency R3/R9 stove.
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R. D. Bighouse, S. G. Barnett, J. E. Houck, and P. E. Tiegs are with OMNI
Environmental Services, Inc., Beaverton, OR 97005.
Robert C. McCrillis is the EPA Project Officer (see below).
The complete report, entitled "Woodstove Durability Testing Protocol," (Order No.
PB95-136164; Cost: $19.50, subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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