Guidance for Quantifying and 

Using Emission Reductions from 

Voluntary Woodstove Changeout 

Programs in State 

Implementation Plans
 

 United States Office of Air and Radiation EPA-456/B-06-001 

Environmental Office of Air Quality Planning January 2006 

Protection Agency & Standards (C304-03) 

________________________________________________________________________ 

Guidance for Quantifying and 

Using Emission Reductions from Voluntary Woodstove 

Changeout Programs in State 

Implementation Plans

Prepared by: 

Information Transfer and Program Implementation Division 

Office of Air Quality Planning and Standards 

U.S. Environmental Protection Agency 

Research Triangle Park, NC 27711 

I
 

TABLE OF CONTENTS 

TABLE OF CONTENTS.............................................................................................................II

LIST OF ABBREVIATIONS.....................................................................................................III

SECTION A: BACKGROUND INFORMATION ........................................................................1

1. What is the purpose of this guidance? ................................................................................ 1 

2. How does this guidance relate to existing Clean Air Act requirements? ........................... 1 

3. For the purposes of this guidance, what is considered a woodstove?................................. 1 

4. What pollutants are emitted by woodstoves in normal intended use? ................................ 2 

5. What is a woodstove changeout progam?........................................................................... 2 

6. What are the benefits of a woodstove changeout program? ............................................... 3 

SECTION B: BASIC CRITERIA FOR USING RWC EMISSIONS REDUCTIONS.......................3

7. What are the basic criteria for using emission reductions in SIPs? .................................... 3 

8. What additional considerations should you be aware of ?.................................................. 4 

9. Are RWC emissions part of the State's or locality’s emission inventory? ......................... 5 

SECTION C: QUANTIFYING WOODSTOVE CHANGEOUT EMISSIONS REDUCTIONS ...........5

10. How do you quantify emission reductions from a woodstove changeout? .................... 5 

SECTION D: MONITORING AND RECORDKEEPING.............................................................5

11. What monitoring and record keeping should occur to document woodstove changeout 

 emissions reductions? ..................................................................................................... 5 

12. What kind of validation and reconciliation should occur for emission reductions in 

SIPs approved as a voluntary measure?.......................................................................... 6 

13. What types of penalties can be assessed for not complying with CAA requirements?.. 6 

SECTION E: INCLUDING WOODSTOVE CHANGEOUT PROGRAMS IN SIPS.........................7

14. What must a State submit to EPA on the woodstove changeout program to meet the 

statutory and regulatory requirements for incorporating a source specific control 

measure in a SIP?............................................................................................................ 7 

15. How can the estimated emission reductions be used for SIP purposes?......................... 7 

SECTION F: CONTACT INFORMATION ................................................................................8

16. Whom should you contact for additional information? .................................................. 8 

APPENDIX A: PM EMISSIONS FACTORS FOR A SELECTION OF WOODSTOVES ..............A1

TABLE A-1 : ADJUSTED PM10 EMISSIONS FACTORS FOR RWC (LB/TON)

A

....................A3

APPENDIX B: GENERAL APPROACH FOR DETERMINING EMISSIONS REDUCTIONS ......B1

TABLE B-1 SUMMARY OF WOODSTOVE NET EFFICIENCIES A ........................................B3

EXAMPLE CALCULATION : ANNUAL PM2.5 REDUCTION FROM A HYPOTHETICAL 1500-STOVE

CHANGEOUT IN THE MID-ATLANTIC REGION ................................................................B3

REFERENCES .......................................................................................................................9

II
 

LIST OF ABBREVIATIONS 

B(a)P Benzo(a)Pyrene

CAA Clean Air Act 

CO Carbon Monoxide

CO2 Carbon Dioxide 

g/kg grams per kilogram

HCl Hydrogen Chloride

NAAQS National Ambient Air Quality 

Standards 

NEI National Emissions Inventory

NOx Nitrogen Oxides

PAH Polycyclic Aromatic Hydrocarbon

PM Particulate Matter (PM10 and PM2.5) 

PM10 PM 10 micrometers or less in 

aerodynamic diameter 

PM2.5 PM 2.5 micrometers or less in 

aerodynamic diameter 

POM Polycyclic Organic Matter

RWC Residential Wood Combustion

SIP State Implementation Plan

SOx Sulfur Oxides

III
Guidance for Quantifying and Using Emission Reductions from Voluntary Woodstove 

Changeout Programs in State Implementation Plans 

(Note: As used in this document, the terms "we", "us" and "our" refer to EPA. The terms "you" 

and "your" refer to a State/local or tribal air pollution control agency.) 

Section A: Background Information 

1. What is the purpose of this guidance?

The purpose of this document is to provide you with guidance on quantifying Residential 

Wood Combustion (RWC) emission reductions from woodstove changeout programs. You may 

wish to use the emission reductions resulting from implementing a woodstove changeout to help 

meet the goal of attaining the PM NAAQS. 

2. How does this guidance relate to existing Clean Air Act requirements?

This document provides guidance to State/local or tribal air pollution control agencies 

and the general public on how woodstove changeout programs to reduce RWC emissions may be 

used to meet SIP requirements. SIP requirements can be found in Sections 110(a)(2) and 172(c) 

of the CAA. This document does not substitute for those provisions, nor is it a regulation itself. It 

does not impose binding, enforceable requirements on any party. Further, it does not assure that 

EPA will approve all instances of its application, and thus the guidance may not apply to a 

particular situation based upon the circumstances. The EPA and State and local decision makers 

retain the discretion to adopt approaches on a case-by-case basis that differ from this guidance 

where appropriate. Any decisions by EPA regarding a particular SIP demonstration will be

made based on the statute and applicable regulations, and only following notice and opportunity 

for public review and comment. Therefore, interested parties are free to raise questions and 

objections about the appropriateness of the application of this guidance to a particular situation; 

EPA will, and States and localities should, consider whether or not the recommendations in this 

guidance are appropriate in that situation. This guidance is a living document and may be revised 

periodically without public notice. The EPA welcomes public comments on this document at any 

time and will consider those comments in any future revisions of this guidance document. 

Readers of this document are cautioned not to regard statements recommending the use 

of certain procedures as either precluding other procedures or information, or providing 

guarantees that using these procedures will result in actions that are fully approvable. As noted 

above, EPA cannot assure that actions based upon this guidance will be fully approvable in all 

instances, and all final actions may only be taken following notice and opportunity for public 

comment. 

3. For the purposes of this guidance, what is considered a woodstove?

Woodstoves are freestanding devices designed to burn cordwood to heat a specific room 

or zone of a house. For the purposes of this guidance document, the term woodstove also 

1
includes fireplace inserts. A fireplace insert is essentially a woodstove that is installed in an 

existing fireplace. 

4. What pollutants are emitted by woodstoves in normal intended use?

RWC emissions are highly variable and are a function of many wood characteristics and 

operating practices. RWC emissions generally contain some combination of gases (principally 

CO and CO2, and some quantity of toxic compounds including, B(a)P, POM, PAH, and others), 

and fine particles (PM2.5) which are composed of tiny unburned particles of ash and toxic 

elements. There are also minor amounts of components such as HCl, SOx, and NOx. In general, 

conditions that promote a fast burn rate and a higher flame intensity enhance secondary 

combustion and thereby lower emissions. Secondary combustion is especially important in 

wood burning because of the high volatile matter content of wood, typically 80 percent by dry 

weight. Conversely, higher emissions will result from a slow burn rate and a lower flame 

intensity. Such generalizations apply particularly to the earlier stages of the burning cycle, when 

significant quantities of combustible volatile matter are being driven out of the wood. Later in 

the burning cycle, when all volatile matter has been driven out of the wood, the charcoal that 

remains burns with relatively few emissions1

. 

5. What is a woodstove changeout progam?

A woodstove changeout is typically a voluntary program initiated by a State or local 

government entity (often a public health agency) to promote the use of cleaner burning heating 

appliances. A variety of incentives are used – such as cash rebates or other financial incentives, 

combined with public outreach and education, to encourage consumers to replace their old, 

inefficient and high polluting woodstoves with new clean burning EPA-certifieda

 woodstoves, or 

other heating appliances such as pellet stoves,b

or gas/electric stoves or fireplaces, or masonry 

heaters. Sometimes, the State or local government may decide to use statutory or regulatory 

means to prevent or limit the use of uncertified woodstoves, such as episodic bans on burning of 

uncertified woodstoves or graduated permit fees. In such circumstances, a woodstove changeout 

program may be instituted as a means to ease the burden on consumers but this does not make 

the changeout program itself mandatory. 

The most effective changeout campaigns include an education component to ensure that 

EPA-certified woodstoves are properly installed, operated and maintained to achieve the lowest 

possible emission rates. Often, the agency sponsoring the changeout makes arrangements with 

metal scrap recycling dealers to recycle the uncertified woodstoves surrendered during the 

changeout, or they are destroyed in accordance with any Federal, State, or local laws governing 

disposal of hazardous or potentially hazardous substances (i.e., creosote). For the purposes of 

taking emissions reduction credit under this guidance, the State or locality should insure that the 

uncertified stoves surrendered in the changeout are accounted for (recycled for scrap metal or 

 

a

 Meets the 40 C.F.R. Part 60 Subpart AAA New Source Performance Standards (“NSPS”) for woodstoves. b

 Pellet woodstoves are fueled with sawdust, wood products, and other biomass materials compressed into pellets. 

Some pellet stove models are subject to the 1988 New Source Performance Standards (NSPS), while others are

exempt due to a high air-to-fuel ratio (i.e., greater than 35-to-1). 

2
destroyed), as they have value on the resale market and could be put back in service. This is a 

crucial step in the process of conducting a changeout if the State or locality wishes to remove the 

uncertified stove’s emissions from the State or locality’s emission inventory and use the 

emissions reductions in their SIP. 

3

 For more information about the practical considerations and the partnership possibilities 

for conducting a changeout in your State, EPA has developed a website: 

http://www.epa.gov/woodstoves/index.html. 

6. What are the benefits of a woodstove changeout program?

 The primary purpose of this guidance is to provide information to help you quantify 

emission reductions resulting from woodstove changeouts. This guidance specifically addresses 

emission reductions of PM2.5, however PM10 emission reductions can also be calculated using the 

same methods and credit can be granted. In addition, there are other important benefits 

associated with reductions in RWC emissions including: 

• Reductions in the emissions of toxic air pollutants resulting in improved indoor and 

outdoor air quality and public health. 

• Reductions in emissions of carbon monoxide and carbon dioxide. 

• Reductions in haze caused by PM2.5 resulting in improved visibility. 

• Reductions in fuel consumption with greater energy efficiency and less maintenance, 

which results in cost savings to the stove owner. 

• Reductions in creosote buildup in chimneys, resulting in lower risk of fire in the home. 

Section B: Basic Criteria for Using RWC Emissions Reductions 

7. What are the basic criteria for using emission reductions in SIPs?

 To be approved as a measure that provides additional emission reductions in a SIP, a 

control measure reducing RWC emissions cannot interfere with other requirements of the CAA, 

and would need to be consistent with SIP attainment and maintenance requirements. Specifically, 

the control measure must provide emission reductions that meet the criteria described below. 

(a) Quantifiable - The emission reductions from a control measure to reduce RWC emissions are 

quantifiable if they can be reliably and replicably measured. Emission reductions must be 

calculated for the time period for which the reductions will be used. Appendix B provides you 

with a sample method for quantifying emission reductions. You can also submit your own 

quantification protocol which we will review and make a determination as to the appropriateness 

of its use on a case-by-case basis. 

(b) Surplus – The emission reductions from a control measure to reduce RWC emissions are 

generally surplus if they are not otherwise relied on to meet other applicable air quality 

attainment and maintenance requirements. In addition, to be considered surplus the emissions 
from woodstoves must be a part of all applicable SIP emissions inventories. This includes 

current and future inventories projected for attainment or maintenance of the NAAQS. 

4

(c) Federally Enforceable – Since woodstove changeout programs are voluntary, the State would 

need to make an enforceable commitment in its SIP to monitor, assess, report and make up, in a 

timely manner, any shortfall in emissions reductions should the expected reductions from the 

changeout program not materialize. Consistent with EPA’s voluntary measures policy described 

below, when the program is voluntary on the part of sources – the program is considered a 

“voluntary measure.” 

Under an existing EPA policy (“Incorporating Emerging and Voluntary Measures in a SIP”c

) the 

State is responsible for assuring that the reductions credited in the SIP occur. The State would 

need to make an enforceable SIP commitment to monitor, assess and report on the emission 

reductions resulting from the voluntary measure and to remedy any shortfalls from forecasted 

emission reductions in a timely manner. Given the uncertainty involved with voluntary and 

emerging measures, we believe it is appropriate in most cases to limit the amount of emissions 

reductions you can take credit for in your SIP. The presumptive limit is 6 percentd

 of the total 

amount of emission reductions required for attainment or maintenance demonstration purposes. 

The limit is presumptive in that EPA believes it may approve measures into a SIP in excess of 

the presumptive six percent where a clear and convincing justification is made by the State as to 

why a higher limit should apply in their case. Any request for a higher limit will be reviewed by 

EPA on a case-by-case basis. 

(d) Permanent - The emission reduction must be permanent throughout the term that the emission 

reduction is used. Documentation of stove replacement, including proof that the stove replaced 

was destroyed or recycled, is key to meeting this requirement and is your responsibility if you 

wish to take credit for woodstove changeout emissions reductions in your SIP. 

(e) Adequately Supported - The State (or responsible agency) must demonstrate that it has 

adequate funding, personnel, and other resources to implement the control measure (in this case a 

woodstove changeout program) on schedule. 

 

8. What additional considerations should you be aware of ?

(a) All uncertified woodstoves surrendered as a part of the changeout, for which you wish to take 

credit for in your SIP, should be located within the nonattainment area boundary in question. 

You may be able to get credit for replacing woodstoves outside of the nonattainment area 

boundary if you can reliably demonstrate that the emissions from these woodstoves are 

 

 c See http://www.epa.gov/ttn/oarpg/t1pgm.html

d The six percent reduction does not apply to an area’s total emission inventory, but only to the increment that is necessary to achieve 

attainment or maintenance. To determine this increment, you must subtract the level of emissions consistent with attaining the NAAQS 

from the projected attainment year inventory, reflecting the benefits of all federal/state regulations that will be adopted and implemented. 
contributing to nonattainment or are adversely affecting maintenance of the PM air quality 

standards. 

5

(b) All EPA-certified woodstoves installed as a part of the changeout should be professionally 

installed. Improper installation can render a woodstove unsafe and cause it to operate with much 

less efficiency which may result in higher rather than lower emissions. You should keep track of 

the number of new certified stoves installed during a changeout program so that you will be able 

to update your emissions inventory and be able to calculate post-changeout emissions reductions. 

9. Are RWC emissions part of the State's or locality’s emission inventory? 

 In order to take credit for these emissions reductions, you will need to insure that an 

adequate and up to date inventory of PM2.5 emissions from woodstoves exists for the area in 

question. In addition, the crediting of emission reductions must also be consistent with the 

assumptions in the emission inventory upon which the attainment or maintenance demonstration 

is based. If they are not already in the SIP inventory, no credit can be given for RWC emissions 

reductions unless the SIP inventory baseline is reassessed to include such emissions at their 

current level. 

Section C: Quantifying Woodstove Changeout Emissions Reductions 

10. How do you quantify emission reductions from a woodstove changeout?

 There are several sources of uncertainty involved with quantifying emissions reductions 

from a woodstove changeout program. Appendices A and B discuss these uncertainties and 

Appendix B provides an example calculation. Generally, the annual emission reductions from 

woodstove changeout programs are based upon the number of uncertified stoves that are 

replaced annually by EPA-certified stoves (or equivalent) minus the number of EPA-certified 

stoves presently in the stove inventory. In some cases, EPA-certified woodstoves may be 

replaced by pellet stoves or other devices such as gas or electric stoves or fireplaces that are 

lower emitting in terms of PM than the device they replaced. This situation can and should be 

accounted for in the inventory and the subsequent emission reduction calculations. If any 

uncertified woodstoves remain in the inventory after the implementation period of the changeout 

program, those emissions must also be included in the post-changeout emissions total. 

 

Section D: Monitoring and Recordkeeping 

11. What monitoring and record keeping should occur to document woodstove changeout

emissions reductions?

(A) For each changeout program generating emissions reductions, the responsible party (the 

State or local air agency in most cases) should monitor and record the following information for 

each time period for which an emissions reduction is generated (or other information capable of 

demonstrating the emissions reductions): 
6

(1) the number of uncertified woodstoves surrendered (scrapped or destroyed) during the 

changeout program, 

(2) a demonstration that either these woodstoves were located in a nonattainment or 

maintenance area for the pollutant for which emission reductions were determined, or if 

not located in the nonattainment area that their emissions contribute to nonattainment or 

adversely affect maintenance of the PM air quality standards. 

(3) the estimated emissions from the uncertified woodstoves for the pollutants of interest, 

(4) the estimated emissions from the woodstoves (or other appliances) that replaced the 

uncertified stoves. 

(B) All information to be monitored and recorded in accordance with this guidance for existing 

SIP requirements should be maintained by the responsible party for a period of no less than five 

years, and available for inspection. 

12. What kind of validation and reconciliation should occur for emission reductions in SIPs

approved as a voluntary measure?

 The SIP submission for a voluntary measure should contain a description of the 

evaluation procedures and time frame(s) in which the evaluation of SIP reductions will take 

place. Once the voluntary control measure is in place, emission reductions should be evaluated 

to validate the actual emission reductions. You should submit the results of your evaluation to 

EPA in accordance with the schedule contained in the SIP. If the review indicates that the actual 

emission reductions are not consistent with the estimated emission reductions, then the amount 

of credit should be adjusted appropriately and applicable remedial measures should be taken. 

See the EPA's “Incorporating Emerging and Voluntary Measures in a SIP” policy for further 

information regarding validation and reconciliation procedures and timing for such measures: 

http://www.epa.gov/ttn/oarpg/t1/memoranda/evm_ievm_g.pdf. 

13. What types of penalties can be assessed for not complying with CAA requirements?

 Use of this guidance does not relieve the responsible party of any obligation to comply 

with all otherwise applicable CAA requirements, including those pertaining to the crediting of 

emission reductions in your SIP for attainment or maintenance plans. To receive SIP credit for 

emissions reductions under a voluntary program such as this the State must make an enforceable 

reconciliation commitment to address any shortfall in emissions reductions which then becomes 

the provision in the SIP subject to enforcement. 

 Violations of CAA requirements are subject to administrative, civil, and/or criminal 

enforcement under Section 113 of the CAA, as well as to citizen suits under Section 304 of the 
CAA. The full range of penalty and injunctive relief options would be available to the Federal or 

State government (or citizens) bringing the enforcement action. 

7

Section E: Including Woodstove Changeout Programs in SIPs 

14. What must a State submit to EPA on the woodstove changeout program to meet the 

statutory and regulatory requirements for incorporating a source specific control measure in a 

SIP?

 The State must submit to EPA a written document that: 

(A) Identifies and describes the woodstove changeout campaign and its implementation 

schedule to reduce RWC emissions within a specific time period; 

(B) Contains a quantification methodology to estimate the emission reductions from the 

woodstove changeout campaign. You can follow the quantification methodology 

provided in Appendix B of this document or you can submit your own. If you submit 

your own quantification methodology for quantifying the emission reductions, you must 

provide all relevant technical support documentation. You must rely on the most recent 

information available at the time the SIP is developed; 

(C) Contains federally enforceable requirements for the responsible party (the State) to 

monitor and record the appropriate information; 

(D) Enforceably commits to evaluate and report the resulting emission reductions of the 

measure as applicable; 

(E) Enforceably commits to remedy any SIP emission shortfall in a timely manner if the 

measure does not achieve estimated emission reductions; and 

(F) Meets all other requirements for SIP revisions under sections 110 and 172 of the 

CAA. 

15. How can the estimated emission reductions be used for SIP purposes?

 For your SIP attainment or maintenance strategy, you should use the emission reductions 

which are expected from the implementation of a woodstove changeout program by applying the 

following criteria: 

a) Only those reductions that occur, or are expected to occur, prior to the area’s attainment 

date are creditable. 

 

b) If the changeout program takes place prior to the attainment date, for example in the 

spring of the attainment year, but the emissions reductions aren’t fully realized until the 
next heating season which ends the following year after the attainment date has past, you 

may need an extension of the attainment date if those emissions reductions are necessary 

to attain the standard. If the extension is approved, all creditable reductions resulting 

from the changeout program that occur before the new attainment date will be considered 

in this instance. 

8

c) Reductions from an ongoing changeout campaign that occur past the area’s attainment 

date, or it’s extension, can be used to support the maintenance plan for the area once it is 

redesignated to attainment, provided the old uncertified stoves surrendered during the 

changeout are scrapped or otherwise removed from service, the number of new stoves 

being installed is tracked, and the responsible agency continues a public outreach 

program to educate the public on the proper techniques for efficiently burning wood. 

Section F: Contact Information 

16. Whom should you contact for additional information?

 State agencies, local agencies, the regulated community and members of the public with 

questions concerning a case-specific application of this guidance should contact the EPA 

Regional Office with responsibility for air quality planning in the area where the woodstove 

changeout is planned. A contact list of EPA Regional Offices is available at the following web 

address: http://www.epa.gov/epahome/locate2.htm. The individuals responsible for SIP 

programs in each office can be found by going to the Regional office website and either using 

the Quick Finder function at the top of each homepage, or by searching on SIP. 

 For general questions regarding this guidance please contact Gary Blais of EPA's Office 

of Air Quality Planning and Standards at (919) 541-3223
Appendix A: PM Emissions Factors for a Selection of Woodstoves 

Emissions estimates are important for developing emissions control strategies, such as voluntary 

woodstove changeout programs. While data from source-specific emission tests or 

continuous emission monitors are usually preferred for estimating emissions, those data are not 

always available and can be expensive to obtain. In situations where area-wide emissions 

estimates for a specific source category – not individual site – are desired, the risks of using a 

poor estimate are low, and the costs of more extensive methods are unattractive, then the use of 

less expensive estimation methods such as emissions factors may be satisfactory and appropriate. 

A 1

If after assessing the risks and costs associated with using emissions factors, sources and 

regulatory authorities determine use of emissions factors to be acceptable, then we offer the 

following information. 

Emissions factors are representative values that attempt to relate the quantity of a pollutant 

released to the atmosphere with an activity associated with the release of that pollutant. These 

factors are usually expressed as the weight of a pollutant divided by a unit weight, volume, 

distance, or duration of the activity emitting the pollutant (e.g., kilograms of particulate emitted 

per megagram of coal burned). Such factors facilitate estimation of emissions from various 

sources of air pollution. In most cases, these factors are simply averages of all available data of 

acceptable quality, and are generally assumed to be representative of long-term averages for all 

facilities in the source category (i.e., a population average). In the case of RWC, our emissions 

factors are expressed in terms of pounds of pollutant per ton of wood burned. 

Currently, the most credible and most widely used source for emissions factors is the EPA’s 

Compilation of Air Pollutant Emission Factors (AP-42). Unfortunately, the AP-42 emissions 

factors for woodstoves are based on old test data. For example, no particulate data for cordwood 

or pellet stoves collected more recently than 1992 are included. As of July 1, 1992, all wood 

heaters sold are required to be "Phase II" certified. Consequently, emissions factors of only the 

earlier models of Phase II certified cordwood stoves and pellet stoves contribute to the 

particulate values compiled in AP-42e

. It is generally recognized in the hearth industry that the 

performance of both Phase II certified cordwood stoves and pellet stoves has improved 

considerably since the earliest models. Also, because most of the testing on which AP-42 

woodstoves emissions factors are based occurred around the time the NSPS was being developed 

(1988-1990), there were not many tests on very old stoves which are believed by many in the 

hearth industry to have much higher emissions. 

OAQPS is considering recommendations to improve AP-42 made by Omni Environmental 

Services (Omni) in a May 26, 2005 report entitled "PM2.5 Emission Reduction Benefits of 

Replacing Conventional Uncertified Woodstoves with Certified Woodstoves or Modern Pellet 

Stoves." Omni has been funded numerous times by EPA to help prepare emissions factors and 

emission inventory guidance for woodstoves as well as by the HPBA. EPA is currently 

 

e Some Phase II cordwood stoves were manufactured and sold before the 1992 requirement became effective and are included in the AP-42 

compilation, but approximately 1 million stoves have been sold since then.
reviewing the complete body of test data and Omni's recommended adjustments. EPA's 

preliminary conclusions are that the logic of the recommendations is sound. It is expected that 

the emissions factors for uncertified stoves will likely increase while the values for newer 

certified stoves will decrease, and thus the emissions reductions due to changing out old stoves 

for new stoves will increase, but the exact magnitudes are pending completion of the review of 

the data and possible additional emissions testing. 

A 2

Omni's recommended adjustments to the National average value take into account the 

"dampered-down" conditions and more frequent start-ups characteristic of stove use in more 

mild climates such as the mid-Atlantic states and the Southeast than the colder climates typical 

of the AP-42 data. Also, Omni recommends adjusting the AP-42 emissions factor for Phase II 

certified stoves to account for the improvement in stove emissions performance since the AP-42 

tests of the late 1980's. The third adjustment would be to increase the efficiency value for 

certified non-catalytic stoves (68% current default value) to reflect the fact that less wood is 

consumed and fewer emissions are produced even if all else is equal. Omni also recommends 

similar adjustments be made for catalytic stoves but not as great due to factoring in catalyst 

degradation. 

Although it is not an "emissions factor" adjustment per se, another significant adjustment to 

woodstove emission estimates that EPA is already planning for is to adjust the wood density 

factor based on better information on representative moisture content. That is, the conversion 

factor (1.16 tons/cord) that many States and EPA used in their inventory development (including 

the 2002 NEI) is low and in the future EPA will revise our methods to have a higher conversion 

factor, perhaps as high as 1.8. We may use state-specific conversion factors, but we know the 

1.16 current nationwide factor is based on oven-dried wood which is not representative of wood 

combusted for residential use. The example calculation in Appendix B uses 1.4 tons/cord, a 

number derived from the MANE-VU RWC survey. 

Until EPA makes a decision about the need for revising AP-42, we recommend using those 

RWC emissions factors found in Table A-1 (below)from the Emission Inventory Improvement 

Program (EIIP), Volume III, Chapter 2, revised final report of January 20012

. The EIIP 

document is considered by EPA to be the most up to date guidance for the development of 

emissions inventories for most source categories, including RWC. Residential woodstoves are 

classified as Phase I, Phase II and Pre-Phase I. Phase II stoves are those certified to meet the 

July 1, 1990, EPA standards; Phase I stoves meet only the July 1, 1988, EPA standards; and PrePhase I stoves do not meet any of the EPA standards but in most cases do necessarily meet the 

Oregon 1986 certification standards. If a stove is certified there will be a label on the back. AP42 contains PM10 emissions factors for catalytic and non-catalytic woodstoves in each of these 

classifications, but only emissions factors for Phase II are presented here. Information on how 

the AP-42 emissions factors were developed can be found in the AP-42 woodstoves section 

(http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s10.pdf). 

At the time of this writing, no factors for PM2.5 are available. If PM2.5 emissions estimates are 

required for an inventory, you may assume that all of the PM10 is PM2.5 (EPA, 1997). Emissions 
estimated using this assumption should not be perceived to be of the same level of quality as 

many of the factors found in AP-42, and if new AP-42 factors for RWC became available, they 

should supersede emissions factors that are presented here. EPA, the hearth industry trade 

association (HPBA), and other stakeholders are currently exploring the issue of revising 

emissions factors for woodstoves, including developing factors specifically for PM

A 3

Table A-1 : Adjusted PM

2.5. 

 

10 Emissions Factors for RWC (lb/ton)a 

Process Description PM10 Emissions Factors 

Residential Total Woodstoves and Fireplacesb 34.6 

Residential Fireplacesc 34.6 

Residential Woodstoves – Catalytic Phase II 16.2 

Residential Woodstoves – Noncatalytic Phase II 14.6 

Residential Woodstoves – Conventional 30.6 

Residential Woodstoves – Pellet / Certifiedd 4.2 

Residential Woodstoves – Pellet / Exempte 8.8 

Masonry Heatersf 5.6 

a State’s Workbook, Methodologies for Estimating Greenhouse Gas Emissions. U.S. Environmental Protection Agency, Office of 

 Policy, Planning and Evaluation. Washington, D.C. 

b These emission factors are for fireplaces and should be used when information separating wood burning equipment types is not 

 available. 

c Exempt from the 1988 New Source Performance Standards for woodstoves because of air: fuel ratio > 15:1 and/or minimum burn rate 

 > 5 kg/hr. 

d Certified pursuant to the 1988 New Source Performance Standards for woodstoves. 

e Exempt from the 1988 New Source Performance Standards for woodstoves because of air: fuel ratio >35:1. 

f Exempt from the 1988 New Source Performance Standards for woodstoves because of weight > 800 kg. 
Appendix B: General Approach for Determining Emissions Reductions 

The purpose of this appendix is to provide a general approach for calculating the net emissions

reductions potential from a voluntary woodstove changeout campaign. You may develop your 

own methodology if you so choose. You are also encouraged to refer to Chapters 3 and 4 of the 

EIIP document referred to in Appendix A for a detailed discussion on the available emissions 

estimation methodologies for RWC. 

B 1

The general approach is to first, determine the PM2.5 emissions from all RWC in the area in 

question for the pre-changeout condition. The first step in this process is to develop an emissions 

inventory and the preferred method of gathering emissions inventory data for RWC is the survey 

method. The alternative method is to estimate activity factors for RWC using residential wood 

data compiled by state or federal agencies, and apportioned using data from the U.S. Census 

Bureau and the U.S. Energy Information Administration3

. The preferred source of information 

on residential wood burning is the state energy office, or state forest service. Available 

information may include estimates of wood burned for residential heating at the state, regional or 

county level. If the state energy office does not have information on residential wood burning, 

other sources of information for area-wide wood use, or per household wood use should be 

identified. USDA Forest Service regional experiment stations may compile information that may 

be useful. Inventory personnel should try to collect the most detailed and area-specific 

information possible. 

The next variable to consider is the emissions factors for the woodstoves in the inventory. An 

emissions factor is a representative value that attempts to relate the quantity of a pollutant 

released to the atmosphere with an activity associated with the release of that pollutant. These 

factors are usually expressed as the weight of pollutant divided by a unit weight, volume, 

distance, or duration of the activity emitting the pollutant (e.g., pounds of pollutant per ton of 

wood burned). The emissions factors used for the preferred method are also used for the 

alternative method. 

After the changeout takes place, determine the RWC PM2.5 emissions and subtract the postchangeout emissions from the pre-changeout emissions to arrive at the net emission reduction. 

Some owners of uncertified woodstoves, and even some owners of certified woodstoves or pellet 

stoves, may decide to switch to natural gas, propane or electric space heating appliances during 

the Changeout campaign. Particulate matter emissions are assumed to be extremely small or 

nonexistent for these devices and thus are not accounted for in this calculation but you are free to 

account for them if you choose. Also, some owners of wood burning heating appliances may 

choose to stop using them entirely as a result of the Changeout campaign and rely instead on 

their primary heating source. This outcome should be reflected in the activity data in the postchangeout condition. The following general equation can be used to determine emissions of any 

source category: 

E = A x EF x (1-ER/100)
B 2

• ER =overall emission reduction efficiency, % 

For RWC, the activity rate is usually expressed in cords of wood used per day and is provided 

either as a single constant or as a range, and should be determined as you develop your emissions 

inventory. Emissions factors are reported in mass of pollutant per mass of dry wood, therefore 

cords need to be converted into mass. The mass of wood in a cord varies with wood species with 

the most significant factor being the difference in the mass of hardwood (deciduous trees) versus 

softwood (coniferous trees). The conversion values reported in the literature range from 

approximately 1.2 tons/dry cord to about 1.8 tons/dry cord. Your State forestry and energy 

offices are good sources for this information in your area. The Emission Inventory Improvement 

Program’s 2005 emission inventory conference

where: 

• E = emissions; 

• A = activity rate 

• EF = emissions factor, and 

f

 featured some informative presentations on 

developing RWC surveys and inventories which might also help you in determining wood fuel 

usage. 

The emissions factors for RWC were covered in the previous appendix. That leaves us with the 

final part of the equation, overall or net efficiency. The net efficiency of a woodstove is the 

product of combustion efficiency and heat transfer efficiency. Table B-1 contains wood stove 

efficiencies taken from AP42.1

 It is by no means a complete and comprehensive list but rather is 

a summary of woodstove net efficiencies by broad categories. 

EPA also maintains a list of EPA-certified woodstoves at: 

http://www.epa.gov/Compliance/resources/publications/monitoring/caa/woodstoves/certifiedwoo

d.pdf which includes an efficiency “rating” from each manufacturer for all the stoves in this list. 

It is not apparent whether this rating is a net efficiency, combustion efficiency, or heat transfer 

efficiency therefore use these ratings with caution if you intend to calculate emissions for 

individual stove models. Consult the manufacturer first to determine the net efficiency. 

 

f See http://www.epa.gov/ttn/chief/conference/ei14/
Table B-1 Summary of Woodstove Net Efficiencies

Source Classification Code

B 3

a

Wood Heater Type Net Efficiency (%) 

Conventional Woodstove 21-04-008-051 54 

Non-catalytic Woodstove 21-04-008-050 68 

Catalytic Woodstove 21-04-008-030 68 

Pellet Stovesb 21-04-008-053 68 

Pellet Stovesc 21-04-008-053 56 

Masonry Heaters 21-04-008-055 58 

a

 Net efficiency is a function of both combustion efficiency and heat transfer efficiency. The 

percentages shown here are based on data collected from in-home testing. 

b

 Certified pursuant to 1988 NSPS 

c

 Exempt from 1988 NSPS (i.e., air-to-fuel ratio >35:1) 

Example Calculation : Annual PM2.5 Reduction from a Hypothetical 1500-Stove 

Changeout in the Mid-Atlantic Region 

The following is presented as an example of how to calculate emissions reductions and is based 

on a hypothetical changeout in the Mid-Atlantic region of the United States involving 1500 

uncertified (“conventional”) woodstoves. It is assumed that the following mix of new certified 

appliances are used to replace the 1500 conventional woodstoves: 1000 certified non-catalytic 

woodstoves, 400 certified catalytic woodstoves, and 100 pellet woodstoves. The average 

national annual cordwood usage value of 1.75 cords/stove/year4

 is assumed and the mass 

conversion factor is assumed to be 1.4 tons/cord5

. 

For this example, the basic equation is modified since we are interested in the improvement in 

emissions based on the change in efficiency from old conventional stoves to newer more 

efficient stoves. Therefore, the equation becomes: 

E = A x EF x (NEconv/NEnew)

where: 

• E = emissions; 

• A = activity rate: (wood fuel usage X mass conversion) 

• EF = emissions factor, and 

• NEx = Net efficiency of the stove 

• Activity Rate = (Cord Use) X (Cord-to-Mass Conversion). 

Assume Cord Use= 1.75 cord/stove/year 

Cord-to-Mass Conversion= 1.4 tons/cord 
B 4

(1.75 cord/stove/year) X (1.4 tons/cord) = 2.45 tons/stove/year. 

Using the modified equation: E = A x EF x (NE

PM

Therefore, the Activity Rate for this region is: 

conv/NEnew)

The Pre-Changeout Emissions are: 

2.5 emissions from 1500 conventional woodstoves = (Activity Rate) X (Emissions Factor) X 

(54% eff. conv /54% eff. conv) X 1500 

Or, 

(2.45 tons/stove/year) X (30.6 lb PM2.5/ton) X 1500 stoves = 112,455 lb PM2.5/year. 

______________________________________________________________________________ 

The Post-Changeout Emissions are: 

PM2.5 emissions from 1000 non-catalytic certified woodstoves = (Activity Rate) X (Emissions 

Factor) X (NEconv/NEnew) X 1000. 

Or: 

(2.45 tons/stove/year) X (54 %eff. conv. / 68 %eff. noncat.) X (14.6 lb PM2.5 /ton) X 1000 stoves = 

28,406 lb PM2.5/year. 

______________________________________________________________________________ 

And: 

PM2.5 emissions from 400 catalytic certified woodstoves = (Activity Rate) X (Emissions Factor) 

X (NEconv/NEnew) X 400. 

Or: 

(2.45 tons/stove/year) X (54 %eff. conv. / 68 %eff. cat.) X (16.2 lb PM2.5 /ton) X 400 stoves = 12,607 

lb PM2.5/year. 

______________________________________________________________________________ 

And, 

PM2.5 emissions from 100 pellet woodstoves = (Activity Rate) X (Emissions Factor) X 

(NEconv/NEnew) X 100. 

Or:

(2.45 tons/stove/year) X (54 %eff. conv. / 68 % eff. pellet) X (4.2 lb PM2.5 /ton) X 100 stoves = 817 lb 

PM2.5/year 

______________________________________________________________________________ 
So, the change in emissions is expressed as Pre-Changeout Emissions - Post-Changeout 

Emissions: 

B 5

(emissions from 1500 conventional stoves) – (emissions from 1000 noncatalytic woodstoves) – 

(emissions from 400 catalytic certified woodstove) – (emissions from 100 pellet stoves). 

(112,455 lb PM

A net reduction of 70,625 lbs of PM

Keep in mind that this calculation is very much a theoretical exercise because in reality, it is 

highly unlikely that there is any community with only conventional woodstoves in the inventory. 

More likely is that there will be some certified appliances, woodstoves and/or pellet stoves, in 

every inventory and some number of gas, electric or propane stoves and you will have to account 

for those emissions both before and after the changeout. Also, it is equally unlikely that any 

changeout will result in all the conventional woodstoves being replaced so the post-changeout 

condition will also include some conventional woodstove emissions. 

Or, 

2.5/yr ) – (28,406 lb PM2.5/yr) – (12,607 lb PM2.5/yr) – (817 lb PM2.5/yr) = 

2.5/year from the pre-changeout condition. 
9 

References 

______________________________________________________________________________ 

1 Compilation of Air Pollutant Emission Factors--Volume I: Stationary Point and 

Area Sources. Fifth Edition Supplement, AP-42, Chapter 1, Section 1.10. U. S. Environmental 

Protection Agency, Office of Air Quality Planning and Standards. (GPO 055-000-00251-7). 

Research Triangle Park, North Carolina. 

http://www.epa.gov/ttn/chief/ap42/ch01/final/c01s10.pdf

2

 Residential Wood Combustion—Volume III, Chapter 2. Prepared by Eastern Research Group, 

Inc., for the Area Sources Committee, Emission Inventory Improvement Program, and U. S. 

Environmental Protection Agency, Office of Air Quality Planning and Standards, Research 

Triangle Park, North Carolina. Revised Final, January 2001. 

http://www.epa.gov/ttn/chief/eiip/techreport/volume03/iii02_apr2001.pdf

3

 See EPA’s Emission Inventory Improvement Program Document Series - Volume 9 

Particulate Emissions, Residential Combustion-Woodstoves: 

http://www.epa.gov/ttn/chief/eiip/techreport/volume09/wdstov3.pdf

4 A Recommended Procedure for Compiling Emission Inventory National, Regional and County 

Level Activity Data for the Residential Wood Combustion Source Category. Houck, J.E., 

Mangino, J.E., Brooks, G. and Huntley, R.H., in proceedings of the U.S. EPA's Emission 

Inventory Conference, Denver, CO, 2001. 

http://www.epa.gov/ttn/chief/conference/ei10/index.html#ses-2

5

 Review of Residential Wood Combustion Data for Mid-Atlantic and New England States, 

Broderick, D.R., Houck, J.E., Crouch, J. and Goldman, J., presented at U.S. EPA's 14th Annual 

Emission Inventory Conference, March 2005.

http://www.epa.gov/ttn/chief/conference/ei14/session9/broderick2.pdf
Office of Air Quality Planning and Standards 

Information Transfer and Program 

Implementation Division 

Research Triangle Park, NC 

United States 

Environmental Protection 

Agency 

Publication No. EPA 456/B-06-

001 

January 2006