1

New Methodology for Estimating Emissions from 

Residential Wood Combustion

Paper #180

Roy Huntley

Emission Inventory and Analysis 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 Analysis Group (EIAG) of the U.S. Environmental Protection 

Agency’s (EPA’s) Office of Air Quality Planning and Standards is in the process of updating 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 

appliances 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 wood burned per 

appliance, appliance populations per county, etc.) into the estimation methodology, 3) to correct 

some known deficiencies in the existing NEI methodology, 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 introduces a

Microsoft Access Tool that was developed to allow S/L/T agencies to calculate annual emissions 

from RWC sources in the future. The Tool is designed to allow users to update county-level 

input parameter (based on local survey or like information) and then easily recalculate countylevel 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 - especially 

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 PM2.5 emissions 

make up about 7 percent of the national inventory mass according to the 2002 National Emission 

Inventory (NEI) on an annual basis; however, local areas can experience much higher 

concentrations in the air during the heating season.

1

In recent years, sales and use of residential woodstoves have been increasing due to rising costs 

of home heating fuel. In addition and over the past 5-years, sales of outdoor hydronic heaters 
2

(OHH) are also strong in the Northern U.S. where they are used as the primary heating 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 included in past inventories because, until 

recently, there were not very many of them in operation.

EPA’s NEI includes emissions data from RWC, which in large part, are submitted 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 states did not submit emissions data from RWC even though EPA 

estimates that this category contributes significantly in many areas to annual PM2.5 and VOC

emissions on an annual basis.

The Emissions Inventory and Analysis Group (EIAG) is in the process of updating 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 hydronic heaters), 2) to make the NEI methodology

easier for states, local agencies, and tribes to input their own location-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 NEI methodology, 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 NEI methodology used to estimate the percent of 

conventional wood stoves versus EPA certified woodstoves was determined in the late 1990’s 

and is in need of updating. Also, the percentage of certified woodstoves can vary widely 

geographically due to local regulations or local woodstove change out programs.

Our approach to performing this update is to develop a MS Access Tool that houses county-level

activity and parameters with queries that allows recalculation of emissions. The Tool has been 

developed to:

 Include previously ignored appliance types, like outdoor hydronic heaters, pellet stoves, wax 

logs, and indoor wood furnaces.

 Provide more transparency.

 Allow flexibility.

 Allow stakeholders to substitute their own tool inputs

 Allow easy updates for future years.

 Use consistent and new Source Classification Codes (SCCs).

 Make use of readily available data.

 Be available from the internet.

Table 1 lists the appliance categories and updated SCCs 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 SCC 
3

update was developed by 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 

efficiency (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 types of inserts 

should use SCC = 

2104008120

Yes 2104008210 Wood Woodstove: fireplace 

inserts; non EPAcertified

Yes 2104008220 Wood Woodstove: fireplace 

inserts; EPA-certified; 

non-catalytic

Yes 2104008230 Wood Woodstove: fireplace 

inserts; EPA-certified; 

catalytic

2104008300 Wood Woodstove: freestanding, 

general

Yes 2104008310 Wood Woodstove: freestanding, 

non-EPA certified

Yes 2104008320 Wood Woodstove: freestanding, 

EPA certified, noncatalytic

Yes 2104008330 Wood Woodstove: freestanding, 

EPA certified, catalytic
4

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, nonEPA certified

2104008520 Wood Furnace: Indoor, 

cordwood-fired, EPA 

certified

2104008530 Wood Furnace: Indoor, pelletfired, general

2104008540 Wood Furnace: Indoor, pelletfired, non-EPA certified

2104008550 Wood Furnace: Indoor, pelletfired, EPA certified

2104008600 Wood Hydronic heater: general, 

all types

Yes 2104008610 Wood Hydronic heater: outdoor

2104008620 Wood Hydronic heater: indoor

2104008630 Wood Hydronic heater: pelletfired

2104008640 Wood Hydronic heater: meets 

NESCAUM phase II 

standards

2104008700 Wood Outdoor wood burning 

device, NEC

Fire-pits and chimeas

Yes 2104009000 Firelog Total: All Combustor 

Types

2104010000 Biomass; 

All Except 

Wood

Total: All Combustor 

Types

OVERVIEW

Calculation Methodology

The emissions from RWC are calculated using the equation below.
5

Ey = u × EFy × CFy (Eq. 1)

where:

Ey = annual emissions (ton/year) for a specific appliance (or SCC)

u = annual activity (tons of fuel burned)

EFy = emission factor (tons of pollutant emitted/mass of fuel used)

CFy = control factor

y is a specific pollutant

Note that CFy was assumed to be 1 for all appliances because emission improvements for RWC 

are represented by improved appliance designs. These were accounted for by applying 

appropriately adjusted emission factors. Each of the terms in the equation and their sources are 

explained further below.

Activity (u)

Methodologies for determining the activity varied by the type of RWC appliance. Activity for 

the majority of appliance types 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 county in 2005

AP = Percentage of occupied housing units for a specific appliance category

(e.g., catalytic woodstoves used as main heating equipment, fireplaces without 

inserts used as supplemental heating equipment, etc.)

BR = Burn rate (cords/year)

D = average density of the wood fuel burned

Outdoor Hydronic Heaters, Indoor Furnaces, and Pellet Stoves

A second method, which applies to outdoor wood burning devices, indoor furnaces, and pellet 

stoves, estimates the number of appliances per county based on state level proportioned to the 

number of woodstoves per county. Activity is calculated using the following formula.

u = AN × BR × D (Eq. 3)

where:

AN = Number of appliances in county

BR = Burn rate (cords/year)

D = average density of the wood fuel burned
6

Number of 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. However these had to be calculated because intercensal estimates of the number 

of occupied housing units by county were not available for 2005 from the U.S. Census – only

annual estimates of the total 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 housing units in each county

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 Broomfield, 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 type listed 

as included in Table 1. In order to estimate county level appliance profiles, several steps were 

needed because county specific appliance counts for the entire nation were not available. Our 

goal was to use easily accessible and publically available data to estimate county-level activity

by appliance type for the entire United States, and let that be the default. Then 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 surveys on the 

Nation’s housing, including household characteristics and heating equipment and fuels.

4

 Both 

the national and metropolitan statistical area (MSA) surveys 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 

years. 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 year until all 47 metropolitan areas are surveyed. Table 2 lists the MSAs 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

Chicago, IL PMSA 2003

Cincinnati, OH-KY-IN PMSA 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

Indianapolis, 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-WI MSA 1998

New Orleans, LA MSA 2004

New York-Nassau-Suffolk-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 Lake City, UT MSA 1998

San Antonio, TX MSA 2004

San Diego, CA MSA 2002

San Francisco, CA PMSA 1998

San Jose, CA PMSA 1998
8

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 Total 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 Fireplace 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 without 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 Wood 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 types: 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, secondary, or pleasure.

The following are the definitions used by the AHS to differentiate between different types of 

equipment ownership, by usage characteristics.

 Main heating equipment – Only one type of equipment was reported as the “Main heating 

equipment,” 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 heating 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 with 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

the main heating equipment.

6

 For example, if the main house is heated with a wood stove, 

and a garage is heated by an electric heat pump, the heat pump would be considered parallel

heating equipment.

The following are the definitions used by the AHS to differentiate between different types of 

RWC Appliances.

 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 circulation system to force the heat into the 

room.

 Wood stove - refers to any range or stove that burns solid fuel including wood burning, pot 

belly, and Franklin stoves.

These population percentages were applied to county-level occupied housing units as described 

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.7In 1999 the estimate was 92 percent uncertified, 

5.7 percent certified using a non-catalytic design, and 2.3 percent certified using a catalytic 

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 catalytic for both fireplace inserts and woodstoves.

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 analysis performed by E.H. Pechan & Associates, Inc. (Pechan) resulted in an 

improvement 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 of occupied housing units in 

a county was used to find the total number of appliances in the county for the majority of

appliance types.

Outdoor Hydronic Heaters and Indoor Furnaces
10

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 by Northeast States for Coordinated Air Use Management (NESCAUM) that was 

provided by 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 states.

For outdoor hydronic 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 the distribution to avoid 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 states, and New York and Pennsylvania. 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). Sales in the southern states 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) states (Maine, Vermont, 

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 by 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 by ratioing 

the state total by the fraction of woodstoves in the county.

For Minnesota, we used information in a recent report from Minnesota Department of Natural 

Resources that provided the number of furnaces by five Minnesota regions.

10

 Furnaces were 

allocated to the county level by ratioing the state total by the fraction of woodstoves in the 

county.
11

For the rest of the Great Lakes states (Wisconsin, Michigan, Illinois, Indiana, and Ohio), we 

generated an average factor from the Minnesota 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 states, we developed a factor from the 2000 Oregon/Washington/Idaho survey

provided by the Oregon Department of Environmental Quality (DEQ). The survey provided the 

percentages of device type by region for 4 of the 5 Oregon regions (we were unable to use data 

from the southeast region due to incomplete central furnace data). The 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. The average of the ratios was 

used to determine the 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 difficult 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 Plainstate surveys performed in the 

1990s (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 

burning purpose (Main, Secondary, and Pleasure). The Access Tool includes the average 

number of cords of wood burned in a year by appliance type. It was 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 factor 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/Sawdust firelogs also heat more efficiently than wood, and it is estimated that their use 

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 would 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 states. The Commercial Buildings Energy Consumption Survey

(CBECS) climate zones are groups of climate divisions, as defined by 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 zones based 

on its 30-year average heating degree-days (HDD) and cooling degree-days (CDD) for the period 

1971 through 2000.

13

 Climate zone is listed in the County Population table. Burn rates for all 

SCCs in the national default were multiplied by the ratio of the average British thermal unit (Btu)

consumption to heat a house each climate zone to the average Btu 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.

8
12

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 by this Tool, and can distinguish between 

Main, Secondary, and Pleasure burn rates. In the event that appliance populations and burn rates 

are not distinguished by burn type (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 type, consequently, burn rates were 

only populated in the secondary burn type.

Wood Density

To compute average density of wood by county, we use the density of oven dried wood because 

emission factors developed by EPA are based on oven dried wood mass units. Dried wood 

density data was obtained from the U.S. Forest Service for various wood species.14 The Forest 

Service developed a database (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 of the uses being fuel wood.

Using the oven dried density by species multiplied by the per-species volumes 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 county to get the average density by county. This average is 

stored in the Density by County table under the pounds per cubic feet (lbs/ft3) column. If a 

county specific density was not available, regional averages were used instead.

The calculated density by county from the Forest Service data was then converted to tons/cords.

Officially a cord is defined as a stack of wood 4 feet wide, 8 feet long, and 4 feet tall or 128 ft3. 

However, to account for air spaces in the stack, we assumed 80 ft3per cord instead.

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 typical 5 pound firelog. For wax 

firelogs, a cord was assumed to be actually 128 ft3because air spaces 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/ft3 was derived. Assuming 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 by 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 (lbs/ft3), but converting and filling in the Density (tons/cord) column by multiplying by

the factor: (80 ft3/cord)/(2000 lbs/ton). The data_source column should be updated 

appropriately as well. When updating or revising the wood density, users should be sure to use 

oven-dried density numbers.
13

Emission Factors

The emission factors used are expressed as tons of pollutant produced for every ton of wood 

burned. The emission factors were reviewed by the task force and for the most part are the same 

as the ones used in past inventories. Some minor changes were implemented. The most 

significant change was to the VOC emissions factor. The old factor was from AP-42 and it was 

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.

DESCRIPTION AND USE OF THE RWC TOOL

The RWC Tool was developed in Microsoft Access to allow S/L/T agencies to calculate annual 

emissions from RWC sources. The Tool is designed to allow users to update county-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 

emissions 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)

Number of

appliances; AN x

(Sales Data)

Number of

appliances

(Census Data)

Burn Rate per

Appliance; BR x

(Cords/year)

Total Volume of

Wood

(Cords)

Wood

Density; D

(Tons/cord)

Total Mass

of Wood

(Tons)

Emission Factor;

EFy

(Tons Pollutant/

Ton Wood)

Emissions; E xy

Census Data Approach

(Fireplaces and Woodstoves)

Appliance Sales Approach

(OHHs and Indoor Furnaces)
14

Table 4. Listing and Descriptions of the Tables Included 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 type corresponding to the SCC.

Burn Rates Entries contain the burn profile, the SCC, the burn purpose, and the 

cords burned per year per appliance.

Density by County Entries contain the county, the density in lb/ft3, 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 by SCC Entries contain the SCC, the Pollutant, the emission factor with 

units, the emission factor converted 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 query will recalculate the emissions accordingly. 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 Profiles 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 any 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 in 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 improved 

percentages are known only for some appliance/burn type 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 complete profile.) The Federal information 
15

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 by dividing the number of appliances per each burn type by 

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 apply 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. Each 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 any or all SCC/burn purpose combinations, a new burn 

profile can be created 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 consequently 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 currently 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 stacked dry cordwood when converting the burn rates. 

The same steps apply as above for supplementing incomplete burn rate data with rates from the 

currently used existing burn profile and providing references for data sources.

Density by County - The Density by County table contains estimates of the average density of 

dry cordwood that is used in residential combustion for every county. Each County has the 

density listed in both lbs/ft3and in tons/cord. The density can be updated for any county or 

counties and the query will recalculate the emissions accordingly.

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/ft3and 

tons/cord assumes 2000 lbs in one ton and 80 cubic feet in one cord.

Other Appliance Populations - The Other Appliance Populations table contains data on the 

number of appliances for SCCs which were not covered by the appliances in the American 
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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 by changing the Number of Appliances column for all affected counties. If the query

is run, it will calculate the updated emissions accordingly.

If more accurate estimates of the appliance population in one or more counties are known, EPA 

should be provided a table of the changes or 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 county when 

the query is run. Users are not encouraged to change this table. Any errors noticed in the current 

emission factor table should be reported to EPA.

CONCLUSIONS

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 users to update county-level input parameter (based on 

local survey or like information) and then recalculate county-level emissions by running a query. 

The Tool 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 format 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 year.

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 Georgia

David Fees, State of Delaware

Julie McDill, Mid-Atlantic Regional Air Management Association

Sally Otterson, State of Washington

Bart Sponsellar, State of Wisconsin

Christal Thompson, State of Alabama

Chris Swab, State of Oregon
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David Wright, State of Maine

REFERENCES

1. U.S. Environmental Protection Agency, “Documentation for the Final 2002 Nonpoint 

Sector (Feb 06 Version) National Emission Inventory for Criteria and Hazardous Air 

Pollutants,” Office of Air Quality Planning and Standards, Air Quality Assessment 

Division, Research Triangle Park, NC, July 2006.

2. Office of the Attorney General Environmental Protection Bureau, “Smoke Gets in Your 

Lungs: Outdoor Wood Boilers in New York State,” March 2008.

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 American 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 26-34, April 

2000.

8. Energy Information Administration, Table CE2-1c, Space-Heating Energy Consumption 

in US Households by Climate Zone, 2001, 

http://www.eia.doe.gov/emeu/recs/recs2001/ce_pdf/spaceheat/ce2-1c_climate2001.pdf

9. Houck, J.E.; Eagle, B.N., “Control Analysis and Documentation for Residential Wood 

Combustion in the MANE-VU Region,” prepared for the Mid-Atlantic Regional Air 

Management Association by OMNI Environmental Services, Inc., December 2006.

10. Minnesota Department of Natural Resources, “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,” OMNI Consulting 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 Agency, November, 2001.

13. Energy Information Administration, “U.S. Climate Zones for Commercial Buildings,” 

retrieved from http://www.eia.doe.gov/emeu/cbecs/climate_zones.html, 2007.

14. U.S. Department of Agriculture, “Timber Products Output Survey,” Forestry Service, 

retrieved via query from http://ncrs2.fs.fed.us/4801/fiadb/rpa_tpo/wc_rpa_tpo.ASP, 

November 19, 2007.

KEYWORDS

Residential wood combustion, National Emissions Inventory, woodstove emissions, fireplace

emissions, wax firelog emissions