1



## New**Methodology for Estimating Emissions from Residential Wood Combustion**  **Paper #180**  **Roy Huntley** Emission Inventory

and Analy sis Group (EIAG) , Office of Air Quality Planning and Standards , U
. S

. Environmental Protection Agency , Research Triangle Park, NC 27711 **John Van Bruggen, Stephen Colodner ,**  **Frank Divita** E.H. Pechan & Associates, Inc. , 5528

- B Hempstead Way , Springfield, VA 22151 

### ABSTRACT The Emissions Inventory and Anal ys is Group ( EI AG ) of the U.S. Environmental Protection Agency ’s ( EPA’s ) Office o f Air Quality Planning and Standards is in the process of updat ing the methodology

it uses to estimate emissions from residential wood combustion (RWC) for the National Emissions Inventory (NEI) . The reasons for doing this are : 1) to account for applianc es not accounted for in the old methodology (e.g., outdoor hydronic heaters) , 2) to make the NEI methodology

easier for state , local, and tribal agencies ( S/L/T ) to input their own location

- specific knowledge (e.g., wood density , estimates of amount of woo d burned per appliance , appliance populations per count y, etc. ) into the estimation methodology , 3) to correct some known deficiencies in the existing NEImethodology , and 4) to make the methodology easier for some users of the NEI (e.g., emission modelers ) to extract appliance population data from the NEI. EPA worked with a group of state , local , and regional planning organization representatives to create the new methodology . This paper describes the new methodology and introduce s a Microsoft Access Too l that was developed to allow S/L/T a gencies to calculate annual emissions f rom RWC sources in the future. The Tool is designed to a llow u sers to update county - level input parameter (based on local survey or like information) and then easily recalculate c ount y level emissions by

running a query

. 

### INTRODUCTION Residential wood combustion (RWC) appliances like fireplaces, fireplace inserts, woodstoves, and hydronic heaters are significant sources of air pollution in the United States

- especiall y during winter months

. RWC emits large amounts of fine particulate matter (PM) , volatile organic compounds (VOCs) , and hazardous air pollutants that in several studies have been shown to contribute to poor human health, air quality , and visibility

. RWC PM 2.5 emissi ons make up about 7 percent of the national inventory mass according to the 2002 National Emission Inventory (NE I) on an annual basis ; however , local areas can experience much higher concentrations in the air during the heating season

. 1 In recent years, s ales and use of residential woodstoves have been increasing due to rising costs of home heating fuel. In addition and over the past 5

- ye ars , sales of outdoor hydronic heaters2

(OHH) are also strong in the Northern U.S. where they are used as the primary he ating source for some homes. These outdoor wood boilers are essentially unregulated by

Federal air pollution regulations and emit , on an average per hour basis, about four times as much fine PM as conventional woodstoves and about 12 times as much as U.S. Environmental Protection Agency ( EPA )

- certified stoves

. 2 These OHHs have not been in cluded in past inventories because , until recentl y, there were not very man y of them in operation. EPA ’s NEI includes emissions data from RWC, which in large part, are s ubmitted by state , local, and tribal (S/L/T) agencies to EPA for inclusion in the NEI. However, when a state does not submit RWC emissions data, the EPA estimates those emissions. For the 2002 NEI, approximately

one - half of the state s did not submit emis sions data from RWC even though EPA estimates that this category contributes significantly

in many areas to annual PM 2.5 and VOC emissions on an annual basis

. The Emissions Inventory and Anal ys is Group ( EI AG ) is in the process of updat ing the methodology it uses to estimate emissions from RWC for the NEI. The EIAG assembled a task force consisting of members of state and local air pollution agencies. See table for names and contact information. Members of the task force are identified in this paper in the Acknowledgements. The reasons for doing this are : 1) to account for appliances not accounted for in the old methodology (e.g., outdoor h ydronic heaters) , 2) to make the NEI methodology easier for state s, local agencies , and tribes to input their own lo cation

- specific knowledge (e.g., wood density , estimates of amount of wood burned per appliance) into the estimation methodology , 3) to correct some known deficiencies in the existing NEImethodology , and 4) to make the methodology

easier for modelers and others of like mind to pull appliance population data from the NEI. In addition, the 2002 NEImethodology used to estimate the percent of conventional wood stoves versus EPA certified wood stoves was determ ined in the late 1990’s and is in need of updating . Also, the p ercentage of certified woodstoves can vary widel y geographically

due to local regulations or local woodstove change out programs. Our approach to performing this update is to develop a MS A c cess Tool that houses count y - level activity and par ameters with queries that allows recalculation of emissions

. The Tool has been developed to :

 In clude previously

ignored appliance ty

pes , like outdoor hydronic heaters, pellet stoves, wax logs, and indoor wood furnaces.  Provide more transparency .  Allow f

l exibility

.  Allow stakeholders to substitute their own tool inputs  Allow eas y update s for future years .  Use consistent and new Source Classification Codes ( SCCs ).  M ake use of readil y available data

.  Be available from the internet

. Table 1 lists the applian ce categories and updated SCC s for RWC sources . The first column of Table 1 indicates which source categories were included in the RWC Tool developed for this project. Note that these SCCs are different from the codes used in the 2002 NEI. The SCC3

updat e was developed b y the RWC work group to add missing appliance types and to avoid double counting of emissions. **Table 1 .**  **Appliance Types and Source Category Codes for RWC Sources**  **. Included**  **SCC Fuel**  **Appliance Type Comment**  Yes 2104008100 Wood Fireplace: general 2104008110 Wood Fireplace: open Conventional fireplace with open hearth 2104008120 Wood Fireplace: enclosed (or otherwise modified) Enclosed with glass doors or other modifications to a conventional fireplace such as devices to boost efficienc y (heat exchangers) 2104008130 Wood Fireplace: qualified for EPA voluntary

program 2104008200 Wood Woodstove: fireplace inserts; general Fireplace inserts are similar to freestanding woodstove but they sit inside a fireplace. Other ty pes of inserts sh ould use SCC = 2104008120 Yes 2104008210 Wood Woodstove: fireplace inserts; non EPA

certified Yes 2104008220 Wood Woodstove: fireplace inserts; EPA

- certified; non - catal yt ic Yes 2104008230 Wood Woodstove: fireplace inserts; EPA

- certified; catal yt ic 2104008300 Wood Woodstove: freestanding, general Yes 2104008310 Wood Woodstove: freestanding, non - EPA certified Yes 2104008320 Wood Woodstove: freestanding, EPA certified, non

catal yt ic Yes 2104008330 Wood Woodstove: freestanding, EPA certified, cataly

tic4

**Included SCC**  **Fuel Appliance Type**  **Comment**

2104008340 Wood Woodstove: freestanding, masonry heater 2104008400 Wood Woodstove: pellet

- fired, general Freestanding or fireplace insert 2104008410 Wood Woodstove: pellet

- fired, non - EPA certified Freestanding or fireplace insert 2104008420 Wood Woodstove: pellet

- fired, EPA certified Freestanding or fireplace insert 2104008500 Wood Furnace: Indoor, general Yes 2104008510 Wood Furnace: Indoor, cordwood

- fired, non

EPA certified 2104008520 Wood Furnace: Indoor, cordwood

- fired, EPA certif ied 2104008530 Wood Furnace: Indoor, pellet

fired, general 2104008540 Wood Furnace: Indoor, pellet

fired, non

- EPA certified 2104008550 Wood Furnace: Indoor, pellet

fired, EPA certified 2104008600 Wood Hydronic heater: general, all ty pes Yes 2 104008610 Wood Hydronic heater: outdoor 2104008620 Wood Hydronic heater: indoor 2104008630 Wood Hydronic heater: pellet

fired 2104008640 Wood Hydronic heater: meets NESCAUM phase II standards 2104008700 Wood Outdoor wood burning device, NEC Fir e - pits and chimeas Yes 2104009000 Firelog Total: All Combustor Ty pes 2104010000 Biomass;

All Except Wood Total: All Combustor

Ty pes 

### OVERVIEW **Calculation Methodology** The e missions from RWC are calculated using the equation below

.5

E y = u × EF

y × CF

y **(Eq. 1)** where: E y = annual emissions (ton/year) for a specific appliance (or SCC) u = annual activity

( tons of fuel burned) EF y = emission factor (tons of pollutant emitted/mass of fuel used) CF y = control factor

y is a specific pollutant Note that CF y was assumed to be 1 for all appliances because emission improvements for RWC are represented by improve d appliance design s. These were accounted for by appl yi ng appropriatel y adjusted emission factors. Each of the terms in the equation and their source s are explained further below. **Activity (u)** M ethodologies for determining the activity varied by the ty pe of RWC appliance. Activity for the majority

of appliance ty

pes was derived from census data

. Fireplaces, Inserts, and Woodstoves For the first method, which applies to fireplaces , fireplace inserts, and woodstoves, activity in terms of tons of fuel burned was calculated based on several factors as shown in the equation below. u = P × AP × BR × D **(Eq. 2)** where: P = Number of occupied housing units in a count y in 2005 AP = Percentage of occupied housing units for a specific appliance category (e.g. , cataly

tic woodstoves used as main heating equipment , fireplaces without inserts used as supplemental heating equipment, etc. ) BR = Burn rate (c ords/ye ar) D = average density of the wood fuel burned Outdoor Hydronic Heaters, Indoor F urnaces, and P ellet S toves A second method , which applies to outdoor wood burning devices, indoor furnaces, and pellet stoves, estimates the number of appliances per county bas ed on s tate level proportioned to the number of woodstoves per county. A ctivity is calculated using the following formula. u = AN × BR × D **(Eq. 3)** where: AN = Number of appliances in county BR = Burn rate (c ords/year) D = average density of the wood fue l b urned6

Number o f Occupied Housing Units in 2005 Since appliance profiles were estimated in terms of the percentage of occupied housing units by appliance type , it is important that county population also be based on number of occupied housing units. H owever these had to be calculated because i ntercensal estimates of the number of occupied housing units by count y were not available for 2005 from the U.S. Census

– only annual estimates of the to tal number of units by county
. It was important to account for this difference because the occupancy rate varies greatly

throughout the country [ e.g., from 98.5 percent in Anoka County, Minnesota to 23 percent in Franklin County , Pennsylvania ]. 3 The 2005 intercensal estimate was used to determine the number of ho using units in each count y and then multiplied by the ratio of occupied housing units to total housing units from the 2000 census to find an estimate of the number of occupied housing units in 2005

. The only exception to this procedure was the county of B roomfield, Colorado, which was established in 2001 and therefore was not in the 2000 census. The percentage of occupied housing units for Boulder County was substituted for Broomfield because in 2000 it was mostly contained in Boulder County

. The number of occupied housing units by county appears in the Tool in the table named County Populations. Development of Appliance Profiles County

- level appliance profiles for RWC sources were estimated for each appliance t ype listed as included in Table 1

. In ord er to estimate county level appliance profiles , several steps were needed because count y s pecific appliance counts for the entire nation were not available

. Our goal was to use easily accessible and publicall y available data to estimate county
- level activ ity by appliance type for the entire United States , and let that be the default. T hen use state or local data as submitted to improve on the default values. Fireplace and Wood Stove The American Housing Survey (AHS) conducts national and metropolitan area survey s on the Nation ’ s housing, including household characteristics and heating equipment and fuels

. 4 Both the national and metropolitan statistical area ( MSA ) survey s are conducted during a 3

- to 7
- month period. The national survey , which gathers information on housing throughout the country , conducts interviews at about 55,000 housing units every 2 years, in odd

- numbered ye ars. The metropolitan area survey consists of 47 metropolitan areas, where householders are interviewed every

6 years . 5 Data is gathered for about 14 metropolitan areas on an even numbered ye ar until all 47 metropolitan areas are surveyed. Table 2 lists the MSA s surveyed in the AHS and the last year a survey was completed in each area. Table 3 provides the 2005 AHS appliance counts by

region. **Table 2. MSAs Gathered in the AHS .** 7

**MSA Year of AHS**  Anaheim

- Santa Ana, CA PMSA 2002 Atlanta, GA MSA 2004 Baltimore, MD MSA 1998 Birmingham, AL MSA 1998 Boston, MA

-NH CMSA 1998 Buffalo, NY CMSA 2002 Charlotte, NC

- SC MSA 2002 Chic ago, IL PMSA 2003 Cincinnati, OH

- KY
- INPMSA 1998 Cleveland, OH PMSA 2004 Columbus, OH MSA 2002 Dallas, TX PMSA 2002 Denver, CO MSA 2004 Detroit, MI PMSA 2003 Fort Worth

- Arlington, TX PMSA 2002 Hartford, CT MSA 2004 Houston, TX PMSA 1998 Indianapo lis, IN MSA 2004 Kansas City , MO

- KS MSA 2002 Los Angeles

- Long Beach, CA PMSA 2003 Memphis, TN

- AR

- MS MSA 2004 Miami

- Ft. Lauderdale, FL CMSA 2002 Milwaukee, WI PMSA 2002 Minneapolis

- St. Paul, MN

- WIMSA 1998 New Orleans, LA MSA 2004 New York

-Nassau
- Su ffolk

- Orange, NY PMSAs 2003 Norfolk

- Virginia Beach

- Newport News, VA

- NC 1998 Northern NJ PMSAs 2003 Oakland, CA PMSA 1998 Oklahoma City , OK MSA 2004 Philadelphia, PA

-NJ PMSA 2003 Phoenix, AZ MSA 2002 Pittsburgh, PA MSA 2004 Portland, OR

- WA PMSA 2002 Providence

- Pawtucket

- Warwick, RI

- MA PMSAs 1998 Riverside

- San Bernardino

- Ontario, CA PMSA 2002 Rochester, NY MSA 1998 Sacramento, CA PMSA 2004 St. Louis, MO

- IL MSA 2004 Salt L ake City, UT MSA 1998 San Antonio, TX MSA 2004 San Diego, CA MSA 2002 San Francisco, CA PMSA 1998 San Jose, CA PMSA 19988

**MSA Year of AHS**  Seattle

- Everett, WA PMSA 2004 Tampa
- St. Petersburg, FL MSA 1998 Washington, DC

- MD
- VA MSA 1998 **Table 3. Example of Regional 2005 AHS Data in Thousands and Percentage .**  **Heating Category Appliance type**  **T otal**  **Northeast Midwest**  **South West**  Main Heating Wood Stove 896 150 143 304 299 Main Heating Fireplace with Inserts 131 14 22 47 47 Main Heating Fireplace without Inserts 59 10 0 22 27 Pleasure Heating Wood Stove 985 258 181 260 286 Pleasure Heating Fir eplace with Inserts 655 74 99 220 263 Pleasure Heating Fireplace without Inserts 391 30 70 133 157 Secondary Heating Wood Stove 3,096 920 635 626 915 Secondary Heating Fireplace with Inserts 4,323 486 829 1,673 1,334 Secondary Heating Fireplace with out Inserts 4,080 371 643 1,686 1,381 **All Houses Total**  **108,871 20,337**  **24,955 39,722**  **23,858** Main Heating Wood Stove 0.82% 0.74% 0.57% 0.77% 1.25% Main Heating Fireplace with Inserts 0.12% 0.07% 0.09% 0.12% 0.20% Main Heating Fireplace without Inserts 0.05% 0.05% 0.00% 0.06% 0.11% Pleasure Heating Wood Stove 0.90% 1.27% 0.73% 0.65% 1.20% Pleasure Heating Fireplace with Inserts 0.60% 0.36% 0.40% 0.55% 1.10% Pleasure Heating Fireplace without Inserts 0.36% 0.15% 0.28% 0.33% 0.66% Secondary Heating Woo d Stove 2.84% 4.52% 2.54% 1.58% 3.84% Secondary Heating Fireplace with Inserts 3.97% 2.39% 3.32% 4.21% 5.59% Secondary Heating Fireplace without Inserts 3.75% 1.82% 2.58% 4.24% 5.79% The AHS provides RWC appliance information for three different appliance ty pes : fireplaces with inserts, wood stoves, and fireplaces without inserts. In addition, AHS data provide information on the purpose of each household heating appliance. These are separated into three categories of heating appliances use - main, se condary , or pleasure

. The following are the definitions used by the AHS to differentiate between different t ypes of equipment ownership, b y usage characteristics.

 Main heating equipment

– Only one t yp e of equipment was reported as the “Main heating equip ment,” as understood by survey respondents. More than one category of “Other heating equipment,” which includes both pleasure and secondary heating equipment, could be reported for the same household.

 Supplemental heating equipment

– This is additional h eating equipment for a heated area of the housing unit. ( AHS Appendix A. http://www.census.gov/hhes/www/housing/ahs/definitions.html

. ) For example, if a home is usually heated w ith main equipment which is oil or natural gas, and the homeowner uses a fireplace at times in winter, the fireplace is considered to be supplemental equipment.9

 Parallel heating equipment

– This is additional heating equipment for an area not heated by th e main heating equipment

. 6 For example, if the main house is heated with a wood stove, and a garage is heated b y an electric heat pump, the heat pump would be considered p arallel heating equipment. The following are the definitions used by the AHS to dif

ferentiate between different types of RWC Appliance s.

 Fireplaces without inserts

- refers to glass door fire screens or fire backs inserted in the back of the fireplace to passively reflect heat.

 Fireplaces with inserts

- have a fan

- forced air circulatio n sy stem to force the heat into the room.

 Wood s tove
- refers to any range or stove that burns solid fuel including wood burning, pot belly , and Franklin stoves. These population percentages w ere ap plied to county
- level occupied housing units as des cribe d above in order to estimate the number of appliances in each county

. The Hearth and Patio Association estimates the proportion of EPA certified wood stoves and inserts to uncertified wood stoves and inserts. 7 In 1999 the estimate was 92 percent uncertif ied, 5.7 percent certified using a non

- cataly tic design, and 2.3 percent certified using a catal yt ic design. EPA estimates an annual growth rate of 1 percent of certified stoves in operation so a case could be made for altering the mix of appliances slightly depending on the age of the latest Hearth and Patio report. 8 One estimate of the ratio in 2005 may be as much as 20 percent certified. For this study , we used a distribution of 80 percent uncertified, 15 percent certified, and 5 percent certified cat aly tic for both fireplace inserts and woodstove s . Fireplaces without inserts were assumed to burn cordwood 78.3 percent of the time, and wax/sawdust firelogs 21.7 percent of the time, and the AHS data was split between the two relevant SCCs accordingly. This was based on the proportion of estimated cordwood equivalent for firelogs to cords consumed in fireplaces without inserts in the 2002 NEI documentation

. 1 The most recent anal ys is performed b y E.H. Pechan & Associates, Inc. ( Pechan) r esulted in an imp rovement that we plan to implement in the 2008 version of this tool. The updated distribution between cordwood and wax/sawdust firelogs is assumed to be 86.5 percent cordwood and 13.5 percent wax/sawdust firelogs. This was based on survey data reflecting the number of households which use wax firelogs exclusively

. 9 These appliance profiles are in the Tool as a table called Appliance Profiles. The product of these appliance profile percentages with the number o f occupied housing units in a county was use d to find the total number of appliances in the county for the m ajority of appliance types. Outdoor Hydronic Heaters and Indoor Furnaces10

For OHHs and indoor furnaces, a different approach was used to find the number of appliances. Sales data was able to provide estimates of the number of appliances within each county

. Outdoor Hydronic Heaters For Outdoor Hydronic Heaters, the population of these appliances were obtained by using sales data compiled b y Northeast States for Coordinated Air Use Management (NESCAUM) that was provided b y Hearth, Patio, and Barbeque Association . The counties populations were estimated by multiplying the state totals by the fraction of woodstoves in the county relative to the state
. Sales data were available for all 50 state s. For outdoor h ydronic heaters, state level sales data by distributing the sales within the state to all counties not in MSAs. This distribution was in proportion to the number of occupied housing units. The counties in the MSAs were not included in th e distribution to avo id assigning high numbers of these units, which are typically found in more rural environments, to cities, based solely on population density

. Indoor Furnaces For indoor furnaces, sales data was able to provide county level estimates of the number of appliances

. 8 The number of appliances for both indoor furnaces and outdoor hydronic heaters is listed in the table Other Appliance Populations in the Tool. Sales of indoor furnaces were very strong in the 1970 ’ s and 1980 ’ s, with the strongest sales in the upper Midwest, the Great Lake state s, and N ew York and Penns yl vania

. After 1988 when the EPA’s NSPS Woodstove rule was promulgated, sales of indoor furnaces have been weak. (Roy Huntley email to Frank Divita of Pechan). S ales in the s outhern state s and in the Pacific Northwest have traditionally not been strong. Several approaches were used to estimate the county level appliance population of indoor furnaces. For the Mid

- Atlantic Northeast Visibility Union ( MANE

- VU ) state s (M aine, Ve rmont, New Hampshire, Massachusetts, Connecticut, New York, Delaware, Maryland, New Jersey , Pennsylvania, Rhode Island, and the District of Colombia), we used the MANE

- VU report to obtain the number of furnaces. 9 The MANE

- VU report provides the number of centralized heaters/furnaces b y state . This figure includes both indoor furnaces and OHH, so taking the difference between this figure and the NESCAUM data for OHH, we were able to estimate the number of indoor furnaces by state . We then allocated these units to the county level b y ratioing the state total by

the fraction of woodstoves in the county

. For Minnesota, we used information in a recent report from Minnesota D epartment of Natural Resources that provided the number of furnaces by five Minnesota regions

. 10 Furnaces were allocated to the count y level by ratioing the state total by the fraction of woodstoves in the county
.11

For the rest of the G reat L akes state s ( Wisconsin, Michigan, Il linois, Indiana, and Ohio ), we generated an average factor from the M innesota report (38 furnaces per 100 woodstoves) for the number of furnaces per woodstove and used the number of woodstoves in each county to estimate the number of furnaces. For the rest of the state s, we developed a factor from the 2000 O regon/W as hington/I daho survey provided b y the Oregon Department of Environmental Quality ( DEQ ) . The survey provided the percentages of device typ e by region for 4 of the 5 O regon regions (w e were unable to use data from the southeast region due to incomplete centr al furnace data). T he central region furnace data as assumed to be represented by indoor furnaces and we therefore used the ratio of the percent of furnaces to the percent of woodstoves by the 4 regions

. T he average of the ratios was used to determine th e number of furnaces in the remaining state not mentioned above. As a last step, we assumed no outdoor furnaces in counties that are in climate zones 4 and 5 Burn Rates Burn rate estimates with the level of detail needed for inventory purposes was diffi cult to come by

. National average burn rates were assumed based on the U.S. Department of Agriculture (USDA ) Forest Service documents from Midwest or Great Plain state survey s performed in the 19 90s (publications available from http://www.ncrs.fs.fed.us/pubs/). Burn rate was differentiated by appliance type (woodstove, fireplace, fireplace with insert, furnace/boiler, and firepit) and burn ing purpose (Main, Secondary , and Pleasure). The Access Tool includes the average number of cords of wood burned in a ye ar b y appliance type. Itwas assumed that these burn rates are based on most of the appliances not being EPA certified. To account for the greater efficiencies of EPA certified appliances, a discount fac tor of 79.4 percent was applied. This means that if an uncertified stove burns 7 cords of wood in a season, a certified stove would burn only 5.55 cords of wood. Wax/Sawdus t firelogs also heat more efficientl y than wood, and it is estimated that their us e displaces more than their volume in wood that would have been burned. Therefore, the burn rates for wax/sawdust firelogs were reduced from those of fireplaces without inserts by a factor of 4.49 , which accounts for the increased volume of wood that woul d be burnt to release the equivalent amount of heat

. 11, 12 County level climate zone were used to adjust burn rate profiles to account for the fact that less wood is burned in warmer state s . The Commercial Buildings Energy Consumption Survey ( CBECS) clim ate zones are groups of climate divisions, as defined b y the National Oceanic and Atmospheric Administration (NOAA), which are regions within a state that are as climatically homogeneous as possible. Each NOAA climate division is placed into one of five z ones based on its 30

- ye ar average heating degree

- day s (HDD) and cooling degree

- days (CDD) f or the period 1971 through 2000

. 13 Climate zone is listed in the County Population table. B urn rates for all SCCs in the national default were multiplied by the ratio of the average British thermal unit ( B tu) consumption to heat a house each climate zone to the average B tu consumption in climate zone 1. The ratios were 0.30 for climate zone 5, 0.44 for climate zone 4, and 0.77 for climate zone 3

. 812

Modifications by S/L/T agencies with more detailed information may be made by

appending a new burn profile to the Burn Rates table in the Access Tool and changing the burn profile number of the appropriate counties in the County Populations table

. Each burn rate profile should address all the RWC SCCs that are considered b y this Tool , and can distinguish between Main, Secondary , and Pleasure burn rates. In the event that appliance populations and burn rates are not distinguished b y burn ty pe (main, secondary , or pleasure ), insert the overall average burn rate in the burn type for which appliance populations are calculated. For example , in Minnesota, appliance populations were all put under the secondary burn t ype, consequently, burn rates were only populated in the secon dary burn t ype. Wood Density To compute average density of wood by

count y, we use the density of oven dried wood because emission factors developed by EPA are based on oven dried wood mass units

. D ri ed wood density data was obtained from the U

. S

. Forest S ervice for various wood species. 14 The F orest S ervice developed a d atabase ( called the timber products output) that contained survey results of sawmill operators that includes the volume of wood by species for several different categories of use - one o f the uses being fuel wood. Using the oven dried density by species multiplied by

the per

- species volume s gave a per species weight which was summed to calculate the total weight for the county . This was then divided by the total volume of wood in the co unty to get the average density by count y . This average is stored in the Density

by County table under the pounds per cubic feet (lbs/ft 3 ) column. If a county specific density

was not available, regional averages were used instead. T he calculated density by county from the Forest Service data w as then converted to tons/ cords. Officiall y a cord is defined as a stack of wood 4 feet wide, 8 feet long, and 4 feet tall or 128 ft 3

. However , to account for air spaces in the stack, we assumed 80 ft 3 per cord i nstead. For wax firelogs, density was assumed to not vary from county to county, and a density of 4.005 tons per cord was used

. This was based on the volume of a ty pical 5 pound firelog. For wax firelogs, a cord was assumed to be actuall y 128 ft 3 becaus e air s paces assumptions are applicable. The density

figure was arrived at based on a Duraflame wax/sawdust firelog, which was measured to have a volume of ~138 cubic inches or ~.0799 cubic feet. From this a density of ~62.58 lb/ft 3 was derived. Assumi ng that for this source type, the equivalent of one cord was 128 cubic feet, we arrived at a density of ~8010 lb/cord or 4.005 tons/cord. The wood density b y county is in the Tool as in the table Density by County . S/L/T agencies can update the appropriate counties with the density of cordwood consumed, filling in not only the Density (lb s /ft 3 ), but converting and filling in the Density (tons/cord) column by

multiplying by the factor: (80 ft 3 /cord)/(2000 lb s /ton). The data_source column should be update d appropriatel y as well. When updating or revising the wood density , users should be sure to use oven - dried density

numbers.13

**E mission Factors**  The emission factors used are expressed as tons of pollutant produced for every ton of wood burned. The emissi on factors were reviewed b y the task force and for the most part are the same as the ones used in past inventories. S ome minor changes were implemented. The most significant change was to the VOC emissions factor. The old factor was from AP

- 42 and it wa s 229 lb VOC /ton of wood burned. The new factor is 18.9 lb VOC/ton of wood burned and it was pulled from the Mid

- Atlantic Regional Air Management Association report. The complete list of the revised emission factors is in the tool

. 

### DESCRI **P TION**  **AND USE OF THE**  **RWC TOOL**  The RWC Tool was developed in Microsoft Access to allow S/L/T agencies to calculate annual emission s from RWC sources . The Tool is designed to allow users to update count y - level input parameter (based on local survey or like information) and then calculate county

- level emissions by running a query

named “Create Calculated Inventory” to generate a table called Calculated Inventory
. Figure 1 provides the flow of the RWC Tool calculations. The shaded boxes in Figure 1 show calculated values which the non

- shaded boxes show data inputs. As shown in Table 4 , the RWC Tool consists of several tables of parameters used to calculate emis sions associated with burning. Each are described below. **Figure 1**  **. RWC Tool Data Flow Diagram .** 

Occupied Units; P (Households) Appliance Profile; AP x (% of Occupied Units)

Num ber o f appliances; AN x (Sales Data) Number of appliances (Census Data) Burn Rate per Appliance; BR x (Cords/year)

Total Volume of Wo od (Cords) Wo od Density; D (Tons/cord)

Total Mass of W ood (Tons) Emission Factor; EF y (Tons Pollutant/ Ton W ood)

Emissions; E xy Census Data Approach (Fireplaces and W oodstoves)
Appliance Sales Approach (OHHs and Indoor Furnaces)14

**Table 4**  **. Listing and D**  **escriptions of the T**  **ables I**  **ncluded in the RWC Tool .**  **Table Name Table Description**  County Populations Entries contain the county, the number of occupied housing units in

2005, the appliance profile, the burn profile, and the climate zone. Appliance Profiles: Entries contain the appliance profile, the SCC, the burn purpose (Main, Secondary , or pleasure) and the percentage of households with an appliance of the ty pe corresponding to the SCC. Burn Rates Entries contain the burn profile, the SCC, the burn purpose, and the cords burned per ye ar per appliance. Density by Count y Entries contain the county, the density in lb/ft 3 , the density

in tons/cord, and the data source. Other Appliance Populations Entries contain the county , the SCC, the burn purpose, and the number of appliances in the county with an appliance of the type corresponding to the SCC. Emission Factor b y SCC Entries contain the SCC, the Pollutant, the emission factor with units, the emission factor conve rted to tons pollutant/tons of wood combusted, and the data source for the emission factor. **County Populations -**  This table lists the number of occupied housing units in each county in the United States . These estimates are based on the 2005 intercensal estimate of total housing units and the percentage of units occupied in 2000. If state or local agencies have performed counts of the number of occupied households per county , these numbers can be substituted into the county

populations table and the que ry will recalculate the emissions accordingl y. More accurate counts of the occupied housing units can be submitted to EPA along with a data source for reference, and they

will be used to replace the current estimates. **Appliance Profiles -**  The Appliance P rofiles table has a number of existing appliance profiles. Each profile provides the percentage of occupied households which utilize each type of wood burning appliance (SCC) and burn purpose combination. If more accurate appliance percentages for an y or all such combinations are available for a state or number of counties, a new appliance profile can be created to accommodate the data. For example, if state or local woodstove change

- out programs result in a higher concentration of certified woodstoves i n a county or counties, this can be accounted for by editing the relative proportion of certified to uncertified woodstoves. It should be noted in the appliance_profile column which appliance profile is currently assigned to the state or counties. If imp roved percentages are known only for some appliance/burn ty pe combinations, the rest should be copied from the original, otherwise all emissions from these sources will be calculated with a value of zero. After adding a new appliance profile with a new number, the appliance_profile column in the county

populations table should be updated for the affected counties. If local agencies have more accurate data, EPA should be provided with a table of both the updated and copied percentages (so as to ensure a co mplete profile.) The Federal information15

processing standard (FIPS) of the counties to which these percentages apply should also be provided, along with a reference for the source of the updated quantities. In the event that actual equipment populations are known, rather than percentages, the percentages must be back

- calculated b y dividing the number of appliances per each burn type b y the county

populations. This will result in a separate new appliance profile for each geographic area in which appliance populations are known. The same steps appl y as above for supplementing incomplete population data with the existing profile data and providing references for data sources. **Burn Rates -**  The Burn Rates table contains a number of existing burn profiles. E ach profile provides the cords burned per year per household for each type of wood burning appliance ( e.g., SCC) and burn purpose combination. If more accurate burn rates are known for an y or all SCC/burn purpose combinations, a new burn profile can be cr eated to accommodate this data. It should be noted in the County Populations table burn_profile column which profile is currently assigned to the state or counties. If improved burn rates are only known for some appliance/burn type combinations, the rest should be copied from the original burn profile, or the amount of wood burned, and consequentl y the emissions, will be calculated as zero. After the addition of a new burn profile with a new number, the affected counties should have the burn_profile column in County Populations updated. If local agencies have more accurate data than is currentl y in the tool, EPA should be provided with a table of both the updated and copied burn rates in cords/year/household. The FIPS of all the counties to which these burn rates should apply should also be provided, along with a reference for the source of the updated burn rates. If the rate at which cordwood is burned is known in terms of cubic feet rather than cords, a cord should be assumed to be 80 cubic feet of st acked dry cordwood when converting the burn rates. The same steps appl y as above for supplementing incomplete burn rate data with rates from the currentl y used existing burn profile and providing references for data sources. **Density by County -**  The Densi ty by County table contains estimates of the average density of dry cordwood that is used in residential combustion for every count y. Each County

has the density listed in both lb s /ft 3 and in tons/cord. The density can be updated for any

count y or counti es and the query

will recalculate the emissions accordingl y. If more accurate estimates of the average wood density exist for one or more counties, the improved data, along with a source reference can be sent to EPA. If this data is used, the data_source column in the Density by County table will be updated with this information. Please note that all densities must be for dry cordwood. Also, the conversion between lbs/ft 3 and tons/cord assumes 2000 lbs in one ton and 80 cu bic feet in one cord. **Other Ap pliance Populations**  **-** The Other Appliance Populations table contains data on the number of appliances for SCCs which were not covered b y the appliances in the American16

Housing Survey . These include pellet

- fire woodstoves, indoor furnaces, and outdoor hydronic heaters. Each county is listed with the number of appliances of each appliance type and burn purpose combination. To model different estimates of the appliance population in one or more counties, this data can be entered b y changing the Number of Ap pliances column for all affected counties. If the query is run, it will calculate the updated emissions accordingl y. If more accurate estimates of the appliance population in one or more counties are known, EPA should be provided a table of the changes o r additions to the table, including all the columns that appear in the table in the tool. **Emission Factor by SCC -**  The Emission Factor by SCC table contains a list of the emission factors that were used to calculate emissions. It also cites the source of each emission factor. Any changes or additions to the emission factors will change the results for every count y when the query is run. Users are not encouraged to change this table. Any errors noticed in the current emission factor table should be repo rted to EPA. 

### CON **C LUSIONS**  An updated methodology was developed as collaboration between EPA, Pechan, and a group of state , local and regional planning organization representatives. In addition, a Microsoft Access Tool was developed in a way that allows u sers to update county - level input parameter (based on local survey

or like information) and then recalculate count y - level emissions by running a query

. The T ool is transparent so that inputs can be easily identified. EPA is interested in obtaining local data that can be used to calculate RWC emissions. Improved data sources in the form at used by the Access Tool can be provided to the authors via email. For everyone’s convenience, Pechan has developed a template that will aid in uploading state specific data to the tool. The template can be obtained by contacting the authors of this paper. As of this writing, EPA is updating the tool for the 2008 calendar ye ar. 

### ACKNOWLEDGEMENTS The authors would like to thank all of the following individuals who were members of the EPA RWC Workgroup who provided data and guidance during the development of the RWC Access Tool . These include: Scott DiBiase, Pinal County , Arizona Di Tian, State of G eorgia David Fees, State of D elaware Julie McDill, Mid

- Atlantic Regio nal Air Management Association Sally Otterson, State of Washington Bart Sponsellar, State of Wisconsin Christal Thompson, State of Alabama Chris Swab, State of O regon17

David Wright, State of M aine 

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. 3. U.S. Census Bureau , American FactFinder, Data Sets, Census 2000 Summary File 3, Quick Tables , Internet address: http://factfinder.census.gov , 2000. 4. United States Census Bureau, “American Housing Survey for the United States: 2005 , Table 2

- 4: Selected Equipment and Plumbing , ” Current Housing Reports, http://www.census.gov/hhes/www/housing/ahs/ahs05/ahs05.html , U.S. Government Printing Office, Washington, DC, 2006. 5. United States Census Bureau, “ American Housing Survey Metropolitan Data,” Current Housing Reports, various years, retrieved from http://www.census.gov/hhes/www/housing/ahs/metropolitandata.html , November 23, 2007. 6. U.S. Census Bureau, “2007 Ameri can Housing Survey data” retrieved from http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html , 2007. 7. Hearth & Home , “ Hearth, Barbeque, and Patio Retailing, 2000 ,” Pages 26

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Information Administration, Table CE2

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Climate Zone, 2001, http://www.eia.doe.gov/emeu/recs/recs2001/ce_pdf/spaceheat/ce2

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- VU Region,” prepared for the Mid

- Atlantic Regional Air Management Association by OMNI Environmental Services, Inc., December 2006. 10. Minnesota Department of Natural Resourc es, “Residential Fuel Wood Assessment

– State of Minnesota, 2002

- 2003 Heating Season,” Division of Forestry , 2005. 11. Houck, J.E., “ Recommended Procedure for Compiling Emission Inventory Data for Manufactured Wax/Sawdust Fireplace Logs ,” OMNIConsulting for the U.S. Environmental Protection Agency , October 2001.18

12. Houck, J.E., “Addendum to: Recommended Procedure for Compiling Emission Inventory Data for Manufactured Wax/Sawdust Fireplace Logs , ” OMNI Consulting for the U.S. Environmental Protection Agen cy , November, 2001. 13. Energy

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### KEYWORDS R esidential w ood c ombustion , National Emissions Inventory , w oodstove e missions , f ireplace e missions , wax firelog emissions