United States Air and Energy Engineering

Environmental Protection Research Laboratory

Agency Research Triangle Park, NC 27711

Research and Development EPA/600/SR-94/193 December 1994

E AP

Woodstove Durability Testing

Protocol

Project Summary

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 measurement of particulate emission factors

with an in-home automated emission

sampler (AES) and by observable physical damage to the woodstove components. Most of the damage appears to

occur when the woodstove is allowed

to operate at exceptionally high temperatures. A method to test the

long-term durability of woodstove models 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 protocol. 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 permitted records of woodstove operating

temperatures, particulate emission levels, and (in some cases) physical degradation to be followed in a real world

setting. The second line of research

was the laboratory “stressing” of various woodstove models under high temperature operation. This laboratory

research has been conducted on six

stoves (five models) and, as with the

in-home research, changes in particulate emission rates were measured and

physical degradation documented. Both

catalytic and noncatalytic stove models, 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 documented in a separate report of the same

title (see Project Report ordering information at back).

Introduction

Recently, there has been much concern by regulatory agencies and stove

manufacturers about long-term physical

degradation of woodstoves and elevated

air pollutant emissions due to this degradation. In the past, such degradation could

be observed only in the field after one or

more heating seasons of use, after a particular 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 protocol by which a woodstove could be operated in the laboratory for a short period of

time (about 1 week) to simulate one heating season in the field. The short turnaround time has been deemed necessary

R. D. Bighouse, S. G. Barnett, J. E. Houck, and P. E. Tiegs
2

to evaluate a stove’s long-term performance 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 target stoves to a cyclic pattern of high

temperature exposures. To maintain consistency, a protocol was developed to

specify all parameters of woodstove burning, including fuel type, moisture, size,

and configuration; loading density; woodstove 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 parameters were held constant, while others

were varied to determine the combination

of factors that would lead to the most

extreme burning condition. The parameters 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 dimension.

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 empirically determined for each stove model

by putting fuel wood loads into operating 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 throughout 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 considered 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 protocol (Blaze King Royal Heir #1) are presented 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 degradation (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 observed to be more severe than that produced by the in-laboratory stress test

protocol. For others, little in-home degradation was observed even after two heating 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 heating season. Each of the protocol variables

has been quantified so that the protocol

can be standardized and used in a reproducible 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 during the design stage to ensure that a

durable stove with low emissions over a

long period of use is produced.
3

Table 1. Observations of Physical Damage Due to Stressing

Blaze

Duration King

of Royal Blaze King

Stressing Heir Royal Heir Country Flame

(days) #11 #2 BBF-6 Regency R3/R9 Quadrafire 3100 Earth Stove 1003C

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4 Some oxidation

and warpage

7 Continued oxidation None

and warpage

Catalyst tested;

still fully active

10 Bypass gap Baffle plate oxidized Minor warping and Some warping and

of 0.64 cm and moderately oxidation of oxidation of

warped (matches Y20, baffle and catalyst holder

Y24) secondary air

tubes

14 Bypass gap of 0.64 cm Test Catalyst holder oxidized

complete and slightly warped

(similar toY14)

20 2 Test complete Extensive baffle Major warping and Failure of bypass

warpage oxidation of mechanism

baffle and (stuck open)

secondary air Severe oxidation

tubes and warping of

catalyst holder

Warped door frame

(not airtight)

25 Catalyst holder oxidized Test complete Test complete Test complete

and warped (identical to

Y14 after two seasons)

35 Still no bypass gap

______________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

1 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.
4

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-94/193

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

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, VA 22161

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