United States Air and Energy EngineeringEnvironmental Protection Research LaboratoryAgency Research Triangle Park, NC 27711

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

E AP

Woodstove Durability TestingProtocol

Project Summary

Woodstove field studies during sevenheating seasons have shown that newtechnology woodstoves designed tohave low particulate emissions havefrequently shown rapid degradation inemission control. This degradation hasbeen documented both by measure-ment of particulate emission factorswith an in-home automated emissionsampler (AES) and by observable physi-cal damage to the woodstove compo-nents. Most of the damage appears tooccur when the woodstove is allowedto operate at exceptionally high tem-peratures. A method to test thelong-term durability of woodstove mod-els in the laboratory in a 1- to 2-weektime frame has been developed andhas come to be referred to as a stresstest.

Two avenues of research have beentaken in developing the stress test pro-tocol. First, the performance ofwoodstoves while in actual in-home usehas been observed during two heatingseasons in three communities: Medfordand Klamath Falls, OR, and Glens Falls,NY. Eight models of stoves in 13 homeswere studied. The field studies permit-ted records of woodstove operatingtemperatures, particulate emission lev-els, and (in some cases) physical deg-radation to be followed in a real worldsetting. The second line of researchwas the laboratory “stressing” of vari-ous woodstove models under high tem-perature operation. This laboratoryresearch has been conducted on sixstoves (five models) and, as with thein-home research, changes in particu-

late emission rates were measured andphysical degradation documented. Bothcatalytic and noncatalytic stove mod-els, including EPA Phase 2 certifiedstoves, were represented in the tests.

This Project Summary was developedby EPA’s Air and Energy EngineeringResearch Laboratory, Research TrianglePark, NC, to announce key findings ofthe research project that is fully docu-mented in a separate report of the sametitle (see Project Report ordering infor-mation at back).

IntroductionRecently, there has been much con-

cern by regulatory agencies and stovemanufacturers about long-term physicaldegradation of woodstoves and elevatedair pollutant emissions due to this degra-dation. In the past, such degradation couldbe observed only in the field after one ormore heating seasons of use, after a par-ticular model had been widely introducedto the market. Consequently, improvementin the manufacturing and design ofwoodstoves in response to degradationhas been slow.

The development of an accelerated testto simulate in-home woodstove aging anddegradation over a short period of time inthe laboratory is reported here. Becausestoves are aged under extreme conditions,the process is termed a “stress test.” Thegoal of the project was to develop a proto-col by which a woodstove could be oper-ated in the laboratory for a short period oftime (about 1 week) to simulate one heat-ing season in the field. The short turn-around time has been deemed necessary

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

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to evaluate a stove’s long-term perfor-mance and durability so that stove designand manufacturing can be modified whilethe stove model is being developed.

Development of a Stress TestStress testing was done to subject tar-

get stoves to a cyclic pattern of hightemperature exposures. To maintain con-sistency, a protocol was developed tospecify all parameters of woodstove burn-ing, including fuel type, moisture, size,and configuration; loading density; wood-stove air settings; startup method; lengthof time doors and bypasses are open;stack height; and criteria for refueling.

Throughout the development of a stresstesting protocol, many of the above pa-rameters were held constant, while otherswere varied to determine the combinationof factors that would lead to the mostextreme burning condition. The param-eters held constant were the following:

Fuel TypeSplit lodgepole pine, as free of knotsas possible.

Fuel Moisture10 to 20% (dry basis).

Fuel LengthFive-sixths of the longest firebox di-mension.

Fuel ConfigurationFuel in center of firebox, packed tightlywith smaller fuel on bottom.

Air SettingsStove settings set to maximize burnrate and firebox temperatures.

Kindling LoadMaximum of 15 minutes in duration.

Length of Bypass OpeningFor catalytic stoves only, bypass openfor additional 7 minutes after stovedoor is closed.

Stack DraftMinimum of 17.4 Pa (0.07 in. H2O) for90% of the burn cycle.

RefuelingA temperature threshold was empiri-cally determined for each stove modelby putting fuel wood loads into oper-ating stoves. The temperature thatcorresponded to the conditions whenthere was first enough space (fromthe burndown of the previous load) toput the full wood load into the stovewas later used as a reloading promptfor each stove model.

Four parameters were varied through-out protocol development, and the effectson temperature were analyzed:

Fuel SizeTwo different fuel sizing regions wereused: (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 througha 13-cm (5-in.) diameter hole. Woodwas considered small if it fit througha 13-cm (5-in.) diameter hole but notthrough an 8-cm (3-in.) diameter hole.

Loading DensityLoading densities used were 48, 112,and 160 kg/m3 (3, 7, and 10 Ib/ft3) offirebox volume.

Length of Door OpeningsStove door was left open between 3and 45 minutes after fuel was loaded.

Stack HeightTwo stack heights were used: (1) 6.1m (20 ft) and (2) 8.2 m (27 ft).

ResultsFive 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 theeffect of protocols 2 through 5. Each stovewas emissions-tested prior to stressingand once again afterwards. Some stovesunderwent extended stress testing. Thephysical degradation is summarized inTable 1. Particulate emissions and a moredetailed description of physical degrada-tion (in both homes and the laboratory)are provided in the report by stove model.

ConclusionsConsiderable variation in woodstove

degradation has been observed in homeusage. For some, degradation was ob-served to be more severe than that pro-duced by the in-laboratory stress testprotocol. For others, little in-home degra-dation was observed even after two heat-ing seasons. Such variability is notsurprising in light of the differences ininstallation, use habits, and fuel types seenwith woodstoves. The research presentedhere shows that deterioration similar tothat caused by 10 days (240 hours) ofstressing a stove following protocol 6 is areasonable predictor of the deteriorationthat may be seen under the more extremein-home usage conditions after one heat-ing season. Each of the protocol variableshas been quantified so that the protocolcan be standardized and used in a repro-ducible manner. This protocol can be usedas a tool to estimate particulate emissionsof a population of aging stoves. It canalso be used by stove manufacturers dur-ing the design stage to ensure that adurable stove with low emissions over along period of use is produced.

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Table 1. Observations of Physical Damage Due to Stressing

BlazeDuration King

of Royal Blaze KingStressing Heir Royal Heir Country Flame

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

4 Some oxidationand warpage

7 Continued oxidation Noneand warpageCatalyst tested;still fully active

10 Bypass gap Baffle plate oxidized Minor warping and Some warping andof 0.64 cm and moderately oxidation of oxidation of

warped (matches Y20, baffle and catalyst holderY24) secondary air

tubes

14 Bypass gap of 0.64 cm Test Catalyst holder oxidizedcomplete and slightly warped

(similar toY14)

20 2 Test complete Extensive baffle Major warping and Failure of bypasswarpage oxidation of mechanism

baffle and (stuck open)secondary air Severe oxidationtubes and warping of

catalyst holderWarped door frame(not airtight)

25 Catalyst holder oxidized Test complete Test complete Test completeand warped (identical toY14 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.

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United StatesEnvironmental Protection AgencyCenter for Environmental Research InformationCincinnati, OH 45268

Official BusinessPenalty for Private Use$300

EPA/600/SR-94/193

BULK RATEPOSTAGE & FEES PAID

EPAPERMIT No. G-35

R. D. Bighouse, S. G. Barnett, J. E. Houck, and P. E. Tiegs are with OMNIEnvironmental 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 fromNational Technical Information Service5285 Port Royal RoadSpringfield, VA 22161Telephone: 703-487-4650

The EPA Project Officer can be contacted atAir and Energy Engineering Research LaboratoryU.S. Environmental Protection AgencyResearch Triangle Park, NC 27711