Process for Developing Improved Cordwood Test 

Methods for Wood Heaters 

Discussion Paper

March 2016

Prepared by

U.S. EPA Office of Air Quality Planning and Standards (OAQPS)

This information is distributed solely for the purpose of discussion and collaboration.

It does not represent and should not be construed to represent any Agency determination or policy.
 

Notice

The EPA promulgated the "Standards of Performance for New Residential Wood Heaters, New 

Residential Hydronic Heaters and Forced-Air Furnaces” on February 3, 2015. The final rule was 

published on March 16, 2015 in 80 FR 13702 for subpart AAA – Standards of Performance for 

New Residential Wood Heaters and in 80 FR 13715 for subpart QQQQ – Standards of 

Performance for New Residential Hydronic Heaters and Forced-Air Furnaces. A complete copy 

of the final rule, including Preamble, can be found in the Federal Register (Volume 80, Number 

50) at https://federalregister.gov/a/2015-03733.

This Discussion Paper puts forth the history and current state-of-the-science regarding cordwood

test methods relevant to the wood heaters regulated under the Standards of Performance cited 

above. The paper also suggests a process for transitioning to test methods that are more 

representative of how cordwood fueled heaters are used in people’s homes. 

Most importantly, this Discussion Paper seeks input from any interested party – from regulators, 

manufacturers, laboratories, third-party certifiers, academia, environmental and health 

organizations and the general public. The Agency seeks a wide range of participation in order to 

further the science. Input on how to improve current cordwood test methods and balance 

representation of in-home use with precision and variability concerns will be useful to EPA as 

the Agency considers the development of a reference method.

The EPA has established a non-rulemaking docket for any input, questions or suggestions 

relevant to this Discussion Paper under Docket ID No. EPA-HQ-OAR-2016-0130. All 

documents in the docket are listed in the www.regulations.gov index. If you want your input to 

be considered in the process, please send by June 30, 2016 to Docket ID No. EPA-HQ-OAR2016-0130, by one of the following methods:

 www.regulations.gov: Follow the on-line instructions for submitting comments.

 Email: a-and-r-docket@epa.gov, Attention Docket ID No. EPA-HQ-OAR-2016-0130.

 Mail: U.S. Postal Service to EPA Docket Center, EPA West (Air Docket), Attention 

Docket ID Number EPA-HQ-OAR-2016-0130, U.S. Environmental Protection Agency, 

Mailcode: 28221T, 1200 Pennsylvania Ave., NW, Washington, DC 20004.

The EPA will post all submitted non-CBI information to this publicly available website. If you 

need to submit CBI material, please contact Amanda Aldridge, EPA, Office of Air Quality 

Planning and Standards (OAQPS) for instructions at telephone number (919) 541-5268, or 

aldridge.amanda@epa.gov.
 

i

Table of Contents

1.0 Introduction...................................................................................................................1

2.0 Why is Wood Smoke Important? ................................................................................3

2.1 Contribution to PM .............................................................................................3

2.2 Local Source of Pollution ...................................................................................4

2.3 Health Impacts....................................................................................................4

3.0 The History and Direction of Wood Heater Appliance Testing ...............................6

3.1 Regulating and Certifying Heating Devices .......................................................6

3.2 Test Methods Prescribed in Current NSPS.........................................................6

3.3 Transition from the 1988 Crib Wood based NSPS to Cordwood.....................15

3.4 What We Know About In-Home Device Use...................................................16

3.5 Capturing Fuel Species Variability including Moisture Content......................18

3.6 Capturing Variability in Burn Rates, Firebox Load and Start-up.....................19

4.0 EPA’s Process for Approving Alternative Test Methods Allowed Under the 

Current NSPS..............................................................................................................23

4.1 Case-by-Case Alternative Test Method Approval............................................23

4.2 Process for EPA to Receive Input on Alternative Test Methods......................24

4.3 Broadly Applicable Alternative Test Method Approval...................................24

5.0 EPA Reference Test Method Development ..............................................................26

5.1 What is an EPA Reference Test Method?.........................................................26

5.2 What are the EPA Reference Test Methods for Wood Heaters? ......................26

5.3 Process for Adopting a New EPA Reference Test Method ..............................27

6.0 Process for Improving Cordwood Test Methods.....................................................28

6.1 Steering Committee Process.............................................................................28

6.1.1 Timeline ...................................................................................................29

6.1.2 Steering Committee’s Charge to the Technical Workgroups..................29

6.2 Technical Workgroup Process..........................................................................31

6.2.1 PM Measurement Method Workgroup ....................................................32

6.2.2 Fueling/Operational Protocol Workgroup ...............................................32

6.3 EPA’s Approval Process for Alternative Methods...........................................34

7.0 Topics for Further Consideration .............................................................................35

8.0 Endnotes for All Sections ...........................................................................................37

9.0 Appendix......................................................................................................................42
ii

Intentionally left blank
1

1.0 Introduction

In August 2014, the Hearth Patio and Barbecue Association (HPBA), the Northeast States for 

Coordinated Air Use Management (NESCAUM) and the Western States Air Resources Council

(WESTAR) presented consensus recommendations to EPA on the subject of test methods for woodburning residential heaters. One such recommendation was: “Wood heater emission limits should be 

based on tests that correlate better with actual in-use emissions than the current test. There is a common 

interest among the parties to transition from the current crib-based wood heater certification test to a 

cordwood-based certification test by first establishing appropriate and efficient test methods, then using

those methods to build a robust database to inform EPA’s determination of BSER for wood heaters 

based on cordwood testing.” They also agreed on the following approach for developing this test 

method: “A workgroup comprised of experts from industry, state/local air quality agencies, and EPA 

will develop protocols for cordwood testing that are sufficiently accurate and reproducible to reliably 

predict emissions from wood heaters throughout the device’s burning cycle.”

1

This document discusses a process to achieve this joint stakeholder recommendation. It brings experts 

together to advance the current science of wood heater testing to better reflect in-home use. The 

dissemination of this Discussion Paper serves as an open invitation to a broad range of stakeholders to 

contribute their expertise and perspective to this endeavor – including regulators, manufacturers, 

laboratories, third-party certifiers, academia, environmental and health organizations, and the general 

public. 

Section 2 highlights the importance of advancing the science of cordwood testing by briefly reviewing 

the health and environmental impacts of wood smoke. Section 3 discusses the history, current status and 

direction of wood heater appliance testing. Included in Section 3 is an overview of the regulating and 

certifying of wood heaters; the test methods currently prescribed in the 2015 NSPS; the transition from 

crib wood to cordwood testing; what we know about in-home device use; and how to capture some of 

the most important aspects of in-home wood heater operation in improved test methods based on 

cordwood. Section 4 describes the EPA process for approving alternative test methods under the current 

NSPS. Section 5 is a brief summary of the process for adopting a new EPA reference test method. 

Section 6 outlines a suggested process for improving cordwood test methods and how EPA will continue 

to approve alternative test methods during this process, including methods based on cordwood. This 

section discusses the process as overseen by a Steering Committee and led by state multi-jurisdiction 

organizations (MJOs). It will include expert participation from a wide range of stakeholders in two 

technical workgroups. One technical workgroup will focus on improvements to the particulate matter 

(PM) measurement method and the other technical workgroup will focus on improvements to the fueling 

and operational protocol of the cordwood based method. The input from these two expert workgroups

will inform improvements in cordwood test methods for wood heaters and the possible development of

an EPA reference test method based on cordwood. The goal of cordwood methods is to reflect in-home 

use, improve the precision of wood heater testing, and be protective of human health and the 

environment as the cornerstone of the NSPS certification program.

Section 7 includes suggested topics for further consideration. Endnotes for all sections are listed in 

Section 8. Finally, Section 9 is an Appendix that includes tables describing the parameters of current 

cordwood based test methods used in the U.S. and in other countries.
2

Table 1. Explanation of Acronyms and Abbreviations

Acronym Explanation

1988 NSPS The New Source Performance Standards (rule) promulgated in 1988 

regulating residential wood stoves 

2015 NSPS The New Source Performance Standards (rule) promulgated in 2015

regulating residential wood heaters that supersedes the 1988 NSPS

AP-42 Air pollution emission factors compilation, published by EPA since 1972

ASTM American Society for Testing and Materials (now ASTM International)

Btu British Thermal Unit

CFR Code of Federal Regulations

CO Carbon Monoxide

cordwood Split logs resembling what a typical homeowner would use for wood fuel

crib wood Douglas Fir dimensional lumber used in many current certification methods

CSA Canadian Standards Association

EN European Standard

EPA U.S. Environmental Protection Agency

FR Federal Register

g/hr Grams per hour

HAP Hazardous Air Pollutants

IBR Incorporated by reference

lb/MMBtu Pounds per million British thermal unit

MJOs Multi-Jurisdiction Organizations

MTG Measurement Technology Group (USEPA)

NAAQS National Ambient Air Quality Standards

NESCAUM Northeast States for Coordinated Air Use Management 

NESHAP National Emission Standards for Hazardous Air Pollutants

NOx Nitrogen Oxides

NSPS New Source Performance Standards

NYSERDA New York State Energy and Research Development Authority

OAQPS Office of Air Quality Planning & Standards (USEPA)

OAR Office of Air and Radiation (USEPA)

PAH Polycyclic Aromatic Hydrocarbon

PM Particulate Matter

PM2.5 Particulate Matter with diameter ≤ 2.5 micrometers ("fine particles")

POM Polycyclic Organic Matter

Subpart AAA The subpart of this rule that regulates new wood stoves (including 

adjustable burn rate stoves, single burn rate stoves and pellet stoves)

Subpart QQQQ The subpart of this rule that regulates new hydronic heaters and new forcedair furnaces

VOC Volatile Organic Compounds 

WESTAR Western States Air Resources Council
3

2.0 Why is Wood Smoke Important?

This section discusses the importance of regulating wood smoke – including wood smoke’s significant 

contribution to particulate matter (PM) pollution, wood smoke’s presence within many neighborhoods 

and homes, and wood smoke’s considerable health impacts.

2.1 Contribution to PM 

Particulate pollution from wood heaters is a significant national air pollution problem and human health 

issue. For almost all of the residential wood heaters currently on the market, there are substantial 

particulate emissions which are composed largely of unburnt carbon and organic compounds. Even 

when the heaters are operated ideally, a fraction of the wood fuel is volatilized but is not completely 

combusted and so condenses to form PM, along with carbon monoxide (CO) and some air toxics.2 Also, 

many users restrict the air flow in order to achieve a longer burn which further increases emissions. 

Under these operating conditions, the combustion quality is reduced even further and emissions can be 

10 or 20 fold greater per unit of fuel compared to adequate air flow conditions.3 

Residential wood smoke contains fine particles (primarily with an aerodynamic diameter of 2.5 

micrometers or less (PM2.5)), CO, toxic air pollutants (e.g., benzene and formaldehyde), and climateforcing emissions (e.g., methane and black carbon). Each year, smoke from wood stoves and fireplaces 

contributes over 382,000 tons of fine particles throughout the country – mostly during the winter 

months.4 Nationally, residential wood combustion also accounts for 20 percent of total stationary and 

mobile polycyclic organic matter (POM) emissions.5

In addition, residential wood smoke causes many counties in the U.S. to either exceed or almost exceed 

the EPA’s health-based national ambient air quality standards (NAAQS) for PM2.5.

6

In places such as 

Keene, New Hampshire; Sacramento, California; Tacoma, Washington; and Fairbanks, Alaska; 

residential wood combustion can contribute over 50 percent of daily wintertime PM2.5 emissions.7It 

may be difficult for these and other areas to meet or continue to meet the PM2.5 standards without taking 

steps to significantly reduce residential wood smoke. Furthermore, studies have shown that PM2.5

concentrations in proximity to a typical outdoor hydronic heater (a.k.a. outdoor wood boiler) can exceed 

the 24-hour PM2.5 NAAQS.8

The National Association of Clean Air Agencies (NACAA), the Environmental Council of States 

(ECOS), NESCAUM, WESTAR, and the Lake Michigan Air Directors Consortium (LADCO) have 

advocated that more stringent standards for new wood heating devices would provide a much needed 

tool for states and local communities to use in addressing the growth of pollution from these sources.9In 

advance of the wood heater 2014 NSPS proposal and 2015 NSPS final rule, EPA received many letters, 

including from NESCAUM, WESTAR, other MJOs, health and environmental organizations, concerned 

citizens, and the HPBA urging the Agency to update and develop regulations for wood heating 

devices.10 A joint letter from NESCAUM and WESTAR cited concerns that many communities are 

measuring ambient conditions above or very close to the PM2.5 NAAQS and that, in many instances, 

emissions from wood smoke are a large contributor to those high PM2.5 levels.11 WESTAR, for example, 

asserted “Residential wood combustion is a leading cause of unhealthy levels of fine particulate and air 

toxics and the primary source of non-attainment with the 24 hour PM2.5 NAAQS in airsheds throughout 

the West.”12
4

In addition, areas currently attaining the PM2.5 NAAQS will experience health benefits from reduced 

residential wood smoke emissions. This is because there is no known threshold below which PM2.5 does 

not cause adverse health effects. Even though the health-based standards are set to provide an adequate

margin of safety, the standards are not set at a level of zero risk. Thus, the EPA recognizes that reducing 

the emissions level in those areas will have health benefits.

2.2 Local Source of Pollution

Wood heaters create significant air quality problems in localities where they are used in large numbers. 

Residential wood smoke can contribute to unhealthy levels of PM2.5 in many neighborhoods nationwide, 

including in minority and low-income neighborhoods, and impact people in their homes. The concerns 

are heightened because wood stoves, hydronic heaters, and other wood heaters are often used around the 

clock in many residential areas. As summarized in EPA’s 1987 listing of residential wood heaters for 

development of the New Source Performance Standards: residential wood combustion PM emissions are 

increasing; they include compounds which are carcinogens; and they are released at low heights in 

residential areas, resulting in relatively high levels of exposure to human populations. Emissions from 

residential wood heating devices occur near ground level in residential communities across the country.

The PM from wood heaters is primarily condensed organic materials as opposed to fly ash. (Fly ash is 

one of the residues of coal combustion.) Unlike large industrial point sources, with sophisticated 

controls such as electrostatic precipitators and with more elevated emission release heights, there are 

millions of residential chimneys emitting wood smoke immediately into their surroundings and 

ultimately into neighbors’ homes. In winter, air pollution is trapped close to the ground – in breathing 

space – because of stagnant air and temperature inversions which limit air movement.13

Furthermore, wood smoke fine particles not only remain in the breathing space air for long periods of 

time, but also readily enter homes and pollute indoor as well as outdoor air. The median amount of 

outdoor fine particle pollution that penetrated indoors was estimated to be 64 percent in one study.14

Consequently, even homes that do not burn wood have higher indoor wood smoke levels if their 

neighbors burn wood.15 For example, significant indoor PM2.5 concentrations and resulting health 

impacts were found in a study conducted by Environment and Human Health, regarding the indoor air in

homes located in the vicinity of outdoor wood heaters (e.g., hydronic heaters).

16 In response to the 2014 

NSPS proposal, the Agency received numerous comments describing the impact of fine PM and other 

wood smoke constituents resulting from wood smoke emissions, including many personal stories of 

specific harm to health from their own or a neighbor’s wood smoke emissions.

2.3 Health Impacts

There is overwhelming recognition of the health impacts of particle pollution, to which wood smoke is a 

contributing factor in many areas. Residential wood combustion in the U.S. accounts for nearly 50 

percent of all area source air toxics cancer risks and 8 percent of noncancer respiratory effects.17 Wood 

smoke contains a mixture of gases and fine particles that can cause immediate health effects, including 

burning eyes, runny nose and bronchitis. Exposure to fine particles has been associated with a range of 

more serious health effects, including aggravation of heart or respiratory problems (as indicated by 

increased hospital admissions and emergency department visits), changes in lung function and increased 

respiratory symptoms, as well as premature death. Populations that are at greater risk for experiencing 

health effects related to fine particle exposures include older adults, children and individuals with preexisting heart or lung disease.
5

Residential wood smoke can increase PM2.5 to levels that cause significant health concerns.18 More than 

80 percent of the PM emissions from wood heaters are smaller than 2.5 micrometers and almost all 

particles are less than 10 micrometers. PM of this size can penetrate to the tracheo-bronchial and 

alveolar regions of the lung. Multiple studies have shown clear associations between PM2.5 exposure and 

increased mortality. There is also growing evidence for the biological mechanisms, which include 

increased risk of ventricular arrhythmia and thrombotic processes, increased system inflammation and 

oxidative stress, increased blood pressure, decreased plaque stability, and lower lung function. Recent 

studies have suggested that risks from PM exposure may extend below the current NAAQS and may not 

have a threshold.19 Furthermore, numerous recent health studies considered in the review of the PM 

NAAQS confirm the impacts on public health. The latest information on the PM NAAQS reviews is at 

http://www.epa.gov/pm/actions.html. 

There is also concern about the health effects of other pollutants found in wood smoke. Wood heaters 

contribute significantly to PM pollution and these appliances also emit CO, volatile organic compounds 

(VOC), nitrogen oxides (NOx) and hazardous air pollutants (HAP). Health effects from CO include:

 Interference with the blood’s ability to carry oxygen to the brain, which impairs thinking and

reflexes;

 Heart pain;

 Lower birth weights and increased deaths in newborns; and

 Death.

Nitrogen oxides can irritate the eyes and respiratory system, may damage the immune system by 

impairing the body’s ability to fight respiratory infection and can affect lung function.20

Residential wood combustion emissions contain potentially carcinogenic (cancer-causing) HAP

including formaldehyde, polycyclic aromatic hydrocarbons (PAHs), benzene and dioxin.21 Health 

effects from formaldehyde and other organic gases include:

 Irritation of eyes, nose, and throat;

 Inflammation of mucous membranes, irritation of the throat and sinuses;

 Interference with lung function;

 Allergic reactions;

 Nose and throat cancer in animals; and 

 Cancer in humans.

As discussed in the preambles for the 2014 NSPS proposal and the 2015 NSPS final rule, emission 

reductions associated with the requirements of this rule will generate substantial health benefits by 

reducing emissions of PM2.5 and HAP, as well as criteria pollutants and their precursors, including CO 

and VOC. (VOCs are precursors of PM2.5 and ozone.) The quantified health benefits of the reduction in 

directly emitted PM2.5 alone is substantial – over 100 times the estimated cost to manufacturers to design 

cleaner devices.
6

3.0 The History and Direction of Wood Heater 

Appliance Testing

This section discusses the history of wood heater appliance testing, including the types of wood heaters 

that are required to undergo certification testing, the test methods used for certification testing, and the 

reason that crib wood has been the basis to-date for certification testing. This section also provides an 

overview of what we know about in-home device use and discusses several important aspects of inhome heater use including: fuel species and moisture content variability, low and high burn rates, 

firebox load, and start-up and refueling emissions.

3.1 Regulating and Certifying Heating Devices

Regulated appliances. The development of the residential wood heater regulations began in the mid1980s in response to the growing recognition that wood smoke contributes to ambient air quality-related 

health problems. The 1988 NSPS regulated catalytic and non-catalytic wood stoves. The 2015 NSPS 

updated the emission standards for catalytic and non-catalytic wood stoves and also applied emission

standards to pellet stoves and single burn rate stoves, as well as to wood-fired residential central heaters 

including hydronic heaters (a.k.a. outdoor wood boilers) and forced-air furnaces (a.k.a. warm-air 

furnaces). Generally speaking, the 2015 NSPS regulates all wood-fired residential heaters, including

cordwood, wood pellet and wood chip fueled devices. Subpart AAA of the 2015 NSPS regulates “room 

heaters” that warm the space surrounding the heater. Subpart QQQQ regulates “central heaters” that 

warm spaces other than the space where the heater is located, by the distribution of heated air through 

ducts or heated liquid through pipes.

Residential Wood Heater Certification program. Because these regulations apply to mass-produced 

residential consumer items, the residential wood heater NSPS allows compliance for model lines to be 

certified “pre-sale” by the manufacturers. To avoid unreasonable cost impacts, both the 1988 and 2015 

NSPS were designed to allow manufacturers of wood heaters to use a certification program to test 

representative wood heaters on a model line basis. Once a model line is certified, all of the individual 

units within the model line are subject to labeling, operational and other requirements. Manufacturers 

are then required to conduct a quality assurance program, which is overseen and verified by a third-party 

certifier, to ensure that appliances produced within a model line conform to the certified design and meet 

the applicable emission limits. There are also provisions in the 2015 NSPS for the third-party certifier 

and for the EPA to conduct unannounced audits to ensure compliance under the certification program.

At the heart of the current certification program are the test methods prescribed in the 2015 NSPS. These 

test methods are discussed in the next subsection. 

3.2 Test Methods Prescribed in Current NSPS

The 1988 NSPS regulated PM emissions from wood stoves and expressed the emission limit in grams 

per hour (g/hr). The test methods used to establish the PM emission value of the wood heaters 

undergoing certification testing include both fueling and operating protocols and sampling and analytical 

PM measurement methods.

Fueling and operating protocol. The EPA developed the wood heater fueling and operating protocol in 

Method 28 as part of the efforts on the 1988 NSPS. In 1987, manufacturers, laboratories, and some 

states provided input to the Agency on the protocol under development. Oregon Method 7 was the 

starting point for Method 28; thus, Method 28 has many aspects similar to Oregon Method 7. The details 
7

on the history and development of Method 28 are contained in the February 18, 1987 proposal in the 

Federal Register (52 FR 5003) and the February 26, 1988 final rule in the Federal Register (53 FR

5866).

The standardized fueling protocol specified fuel species (Douglas Fir dimensional “crib” lumber), and 

the allowable moisture content range prescribed in Method 28 serve the purpose of providing a common 

basis for comparing emission performance among wood heaters for certification testing purposes. As 

explained in the 1988 NSPS, standardized test methods are necessary to achieve objective comparison 

among heaters and comparison of emission performance of individual heaters to a specified regulatory 

limit. There are multiple parameters, some of which are routinely varied by the operator, that affect the 

burn rate and combustion quality of natural draft wood heaters. Ideally, a standardized test method 

creates reproducible test conditions that are necessary for comparing performance of one heater to 

another. Furthermore, manufacturers, laboratories, states and the EPA have more than 25 years of 

experience with Method 28, and it has been very useful for certifying hundreds of model lines of wood

heaters/stoves. In addition, EPA Method 28 WHH (for wood-fired hydronic heaters) is based on Method 

28 and has been used for qualification testing of hydronic heaters in the EPA voluntary partnership 

program and numerous state regulations.

Nonetheless, the EPA and stakeholders widely agree that improved test methods for residential wood 

heaters are needed in order to better reflect wood heater operation in homes across the country. Prior to 

the 2014 NSPS proposal, the EPA asked the manufacturers, EPA-accredited laboratories and states for 

their insights on Method 28. Many stakeholders agreed that changes needed to be made to improve the 

reproducibility and repeatability of the test procedures and to address concerns about how to best ensure 

protection across the entire U.S. when various operating scenarios are used and various wood species 

and densities are used. The test methods prescribed by the Agency in the 2015 NSPS – including a 

revised Method 28 and several other fueling and operating protocols depending on the type of wood 

heater to be certified – include some of these improvements. However, the fueling and operating test 

methods prescribed by the 2015 NSPS (listed in Table 2) represent a step in the process toward better 

test methods, rather than the end goal. There is still room for improvement, as discussed in this 

document.

Sampling and analytical PM measurement. Procedures for measuring particulate emissions from wood 

heaters involve measurement of exhaust gas flow rate and emission concentration. These measurements 

can be made either in the wood heater stack or in a dilution tunnel. A dilution tunnel is a device which 

captures wood heater stack emissions and introduces outside air for the purpose of maintaining constant 

measurable gas velocities for sampling. The 1988 NSPS required either Method 5G (using a dilution 

tunnel sampling location) or Method 5H (using a stack sampling location) to measure PM, with a 

conversion factor to better equate 5H and 5G PM results in order to establish a device’s emissions while 

undergoing certification testing. The adjustment between Methods 5G and 5H has resulted in as high as 

a 30 percent difference in certification values. Furthermore, Houck et.al. note that “[i]t is generally 

agreed that a dilution tunnel approach collects particles in a more realistic fashion and more closely 

simulates the formation of particles once emissions from chimneys mix and cool in the ambient air than 

a method such as Method 5H based on the old industrial stack sampling Method 5.”

22 This is because a 

dilution tunnel allows the flue gas to cool and the PM to condense. By the time the gas reaches the filter 

(at ≤ 90 degrees), PM has formed that much closer approximates actual residential near-flue conditions 

than sampling directly in the flue would via Method 5H. For these reasons, Method 5H is no longer 

allowed to be used for certification under the 2015 NSPS.
8

The Agency continues to recognize – as it did in the 1988 NSPS – that test methods are an integral part 

of any regulation and that the emission limit is related directly to the method. This is especially true for 

PM because PM is not an absolute quantity, but rather is defined by the measurement method (i.e., it is 

an operationally defined quantity). Different methods produce different PM emission results because 

wood combustion particles (formed by condensed organic compounds) are trapped with different 

efficiencies depending on the PM sampling method used.23 Application of more than one measurement 

test method could needlessly complicate enforcement and may even result in unequal enforcement of the 

standards. Because of these considerations, in the 2015 NSPS the Agency requires the use of one PM 

test method (ASTM E2515-11, a dilution tunnel method) for the measurement of PM across all devices,

using the prescribed fueling and operating protocols with the exception of test method EN 303-5. While 

Method 5G is not prescribed in the 2015 NSPS, it is not prohibited from being used in an alternative test 

method if prior approval is received from the EPA. For example, the EPA would consider the existing 

Method 5G for use with the draft ASTM Cordwood method, if requested. However, in that instance, the 

EPA would likely include several caveats upon approval to align it with EPA’s current approach to 

cordwood PM measurement from wood stoves (i.e., ASTM 2515 with some modifications). Section 4

describes the EPA’s process for approval of alternatives and modifications to test methods and testing 

procedures.

Efficiency and CO reporting. Stakeholders have pointed out the usefulness of reporting to consumers the 

efficiency of each wood heater on the market, based on a common metric, so that consumers have the 

information necessary to choose a heater needing less fuel. In addition, stakeholders and the EPA 

continue to recognize the importance of measuring and reporting CO emissions from all regulated wood 

heaters, due to the immediate health dangers to consumers and the negative environmental effects of 

emitted CO. The 2015 NSPS, therefore, prescribes a common test method (CSA B415.1-10) across all 

devices for measuring efficiency and CO emissions.

Test methods prescribed in the 2015 residential wood heater NSPS. Table 2 lists all the test methods 

prescribed in the 2015 NSPS – both fueling and operating protocols, as well as sampling and analytical 

measurement methods. The table includes a brief description of each method, the applicable residential 

wood heating device(s), and information regarding how each protocol or sampling method prescribed in 

the 2015 NSPS handles the following parameters:

 Fuel species and density;

 Moisture content;

 Fueling protocol;

 PM measurement;

 Efficiency measurement; and

 CO measurement.
9

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Fueling & Operating Test Methods for Adjustable & Single Burn Rate Stoves and Pellet Stoves under Subpart AAA

EPA Method 28R 

for Certification 

and Auditing of 

Wood Heaters

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for measuring 

PM emissions from wood-fired room heaters and 

fireplace inserts. Four burn rate categories (kg/hr of 

wood fuel burned) are used to calculate the weighted 

average emission rate, based on a hot-to-hot (no cold 

start) test cycle. The method incorporates the 

provisions of ASTM E2780-10 except that the 

startup, burn rate categories, low burn rate 

requirement and weightings of Method 28 must be 

used. Knowledge of EPA Methods 1, 2, 3, 4, 5, 5G, 

5H, 6, 6C and 16A is assumed. ASTM E871-82 may 

be used as an alternative to the moisture content 

determination procedures in Method 5H and Method 

28 for particulate wood fuel.

Catalytic and noncatalytic adjustable 

burn rate stoves, 

using g/hr metric 

based on a weighted 

average. (References 

ASTM E2780-10 

which contains an 

appendix for the 

fueling & operating 

protocol for single 

burn rate stoves.)

“Crib Wood” 

dimensional 

lumber, 

Douglas Fir,

untreated, 

certified C 

grade or better, 

air-dried with a 

16-20% wet

basis (19-25% 

dry basis) 

moisture 

content

PM emissions 

must be measured 

by the dilution 

tunnel method 

specified in ASTM 

E2515-11.

CSA B415.1-10 

must be used to 

measure efficiency 

(stack loss 

method), CO and 

heat output.

ASTM E2779-10 

Standard Test 

Method for 

Determining 

Particulate Matter 

Emissions from 

Pellet Heaters

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for determining 

PM emissions from pellet or other granular or 

particulate biomass burning room heaters and 

fireplace inserts. An integrated hot-to-hot (no cold 

start) test run is conducted including 3 burn rate 

segments ranging from low to maximum. A separate 

test run is required for each fuel type specified by the 

manufacturer. If more than one grade of pellets is 

listed for the heater, the lowest recommended grade 

is used as test fuel.

Incorporated by 

reference (IBR) in 

NSPS for pellet 

stoves, using a g/hr

metric based on an 

average emission 

rate (total emissions 

divided by length of 

full test run)

Pellet fuel with 

the fuel type(s) 

specified by the 

manufacturer;

Douglas Fir is 

allowed; NSPS 

requires pellets 

to be graded 

and licensed

PM emissions 

must be measured 

by the dilution 

tunnel method 

specified in ASTM 

E2515-11. CSA 

B415.1-10 must be 

used to measure 

efficiency (stack 

loss method), CO 

and heat output.
10

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Fueling & Operating Test Methods for Adjustable & Single Burn Rate Stoves and Pellet Stoves under Subpart AAA

ASTM E871-82

(Reapproved 2013) 

Standard Test 

Method for 

Moisture Analysis 

of Particulate Wood 

Fuels

Moisture Analysis Determination – This method 

covers the determination of the total mass basis 

moisture in the analysis sample of particulate wood 

fuel. IBR in NSPS as an acceptable alternative to 

EPA Methods 5H and 28 for moisture analysis of 

particulate wood fuel. It is also used in ASTM 

E2779-10 for testing of pellet heaters.

Any heater regulated 

under Subpart AAA 

if using any of fuel 

types listed under 

“Allowable Fuel 

Species”

Sanderdust, 

sawdust, pellets, 

green tree chips, 

hogged fuel, or 

other particulate 

wood fuel with 

max particle 

volume of 1 in3

This is a moisture 

analysis method

based on total 

mass

ASTM E2780-10

Standard Test 

Method for 

Determining 

Particulate Matter 

Emissions from 

Wood Heaters

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for determining 

PM emissions from wood-burning room heaters and 

fireplace inserts. The fuel load specified is a lumber 

crib of uniform dimensions, identical to that specified 

in EPA Method 28 and each test run is a hot-to-hot 

(no cold start) cycle. NSPS stipulates that Method 28 

burn rate categories must be used (instead of low, 

medium and maximum rates of method). This 

method also includes Annex A1 which provides a 

fueling procedure using cordwood. 

Catalytic and noncatalytic adjustable 

burn rate stoves, 

using a g/hr metric 

based on a weighted 

average. IBR in 

Method 28R, 

although the startup, 

burn rate categories, 

low burn rate 

requirement and 

weightings in 

Method 28 must be 

used. Appendix in 

method also contains 

protocol for single 

burn rate stoves.

“Crib Wood” 

dimensional 

lumber 

(standard grade 

or better 

Douglas Fir);

method allows 

15-25% 

moisture 

content (wet 

basis); specifies 

an average 

density of 25-36 

lb/ft3. Method 

also includes 

Annex with

cordwood

protocol.

PM emissions 

must be measured

by the dilution 

tunnel method 

specified in ASTM 

E2515-11.

CSA B415.1-10 

must be used to 

measure efficiency 

(stack loss 

method), CO and 

heat output.
11

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Fueling & Operating Test Methods for Hydronic Heaters under Subpart QQQQ

EPA Method 

28WHH for 

Measurement of 

Particulate 

Emissions & 

Heating Efficiency 

of Wood-Fired 

Hydronic Heating 

Appliances

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for measuring

PM emissions at specified heat output rates (Btu/hr)

based on the rated heating capacity. Procedures for 

determining burn rates, and particulate emissions 

rates and for reducing data are provided. Method 28, 

ASTM E2515-11 and CSA B415.1-10 are referenced. 

Heater is operated on a hot-to-hot (no cold start) test 

cycle and the four test categories / burn rates are as 

follows: Category I = heat output of ≤ 15% capacity; 

Category II = 16-24% capacity; Category III = 25-

50% capacity; Category IV = heat output capacity

Indoor and outdoor 

hydronic heaters, 

both pressurized and 

non-pressurized, 

using an annual 

average lb/MMBtu 

output metric 

“Crib Wood” 

dimensional 

lumber

composed of 

red or white 

oak, with a 19-

25% dry basis 

moisture 

content

PM emissions 

must be measured 

by the dilution 

tunnel method 

specified in ASTM 

E2515-11. 

Thermal efficiency 

(stack loss 

method) and CO 

emissions must be 

measured using 

CSA B415.1-10

EPA Method 

28WHH-PTS for 

Certification of 

Cordwood-Fired 

Hydronic Heating 

Appliances with 

Partial Thermal 

Storage

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for measuring 

PM emissions at specified heat output rates (Btu/hr) 

referenced against the rated heating capacity. 

Procedures for determining heat output rates, PM and 

CO emissions, and efficiency and for reducing data 

are provided. Methods 28, 28WHH and CSA B415.1-

10 are referenced. The four test categories are the 

same as in Method 28WHH, but the Category III and 

IV runs use a hot-to-hot test cycle, while the 

Category I and II runs use a cold start. Category I and 

II runs must be done with thermal storage; Category 

III and IV runs may be done with or without thermal 

storage. Three burn cycle phases: start-up (from the 

start of the test until 15 percent of the test fuel charge 

is consumed); steady-state (from the end of the startup phase to a point at which 80 percent of the test 

fuel charge is consumed); and end phase.

Indoor and outdoor 

hydronic heaters

equipped with 

external partial 

thermal storage, both 

pressurized & nonpressurized, using an 

annual average 

lb/MMBtu output 

metric. Note that 

method produces a

PM emission rate 

(g/hr) based on startup, steady state and 

end phases of the 

burn cycle.

Cordwood

composed of 

red or white 

oak, with a 19-

25% dry basis 

moisture 

content with 

cross section 

dimensions and 

weight limits as 

defined in CSA 

B415.1-10. 

Dimensional 

lumber is not 

allowed by this 

test method.

PM emissions 

must be measured 

by the dilution 

tunnel method 

specified in ASTM 

E2515-11.

Thermal efficiency 

(stack loss 

method) and CO 

emissions must be 

measured using 

CSA B415.1-10
12

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Fueling & Operating Test Methods for Hydronic Heaters under Subpart QQQQ

ASTM E2618-13

Standard Test 

Method for 

Measurement of 

Particulate Matter 

Emissions and 

Heating Efficiency 

of Outdoor Solid 

Fuel-Fired 

Hydronic Heating 

Appliances

Fueling & Operating Protocol - This method covers 

the fueling and operating procedures for measuring 

PM emissions at specified heat output rates based on 

the heater’s rated heating capacity. Heater is operated 

on a hot-to-hot test cycle for the same four test 

categories used in Method 28WHH (above). Method 

references ASTM E2515-11 and CSA B415.1-10. 

NSPS requires use of this method for continuously 

fed biomass hydronic heaters. Annex A1 of method 

applies to full thermal storage hydronic heaters and 

Annex A2 applies to partial thermal storage hydronic 

heaters; cold start is incorporated in method for 

heaters with thermal storage.

Indoor and outdoor 

hydronic heaters, 

both pressurized and 

non-pressurized, 

including no, partial 

and full thermal 

storage heaters,

using an annual 

average lb/MMBtu 

output metric.

Cordwood and 

automatically 

fed biomass

fuel, any wood 

species within 

specified 

density range 

allowed with a 

19-25% dry 

basis moisture 

content,

Douglas Fir 

(crib wood) also 

allowed

PM emissions 

must be measured 

by the dilution 

tunnel method 

specified in ASTM 

E2515-11.

Thermal efficiency 

(stack loss 

method) and CO 

emissions must be 

measured using 

CSA B415.1-10

EN 303-5 Heating 

boilers for solid 

fuels, manually and 

automatically 

stoked nominal heat

output of up to 500 

kW

Fueling & Operating Protocol - This European 

standard provides a fueling and operating procedure 

for measuring PM emissions that is allowed to certify 

to the 2015 hydronic heater standard for units sold 

with thermal storage only; it is not allowed to certify 

to the 2020 standard. Emissions from manually fed 

heaters using this method are based on the average 

from 2 consecutive combustion periods, with the 

mean value based on time elapsed only, without 

regard to the flue gas flow rate. In the method, mean 

values are measured in ppm which are then converted 

to mg/m3based on provided conversion factors.

Hydronic heaters up 

to 500 kW size, 

manually or 

automatically 

stoked, using a 

mg/m3output metric 

(converted to 

lb/MMBtu for the 

NSPS) based on an 

average over 2 

periods at full load

Cordwood with 

option of beech, 

birch, oak, 

spruce or 

hornbeam with 

a moisture 

content of 12-

20% (as 

received basis)

In-stack 

measurement of 

PM with the 

addition of organic 

gases. Thermal 

efficiency (stack 

loss method) and 

CO emissions 

must be measured 

using CSA 

B415.1-10
13

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Fueling & Operating Test Methods for Forced-Air Furnaces under Subpart QQQQ

CSA B415.1-10

Performance 

Testing of Solidfuel-burning 

Heating Appliances

Fueling & Operating Protocol - This Canadian 

Standard is a method covering the fueling and 

operating procedures for measuring PM emissions, 

CO emissions, heat output, appliance efficiency, and 

flue gas flow rates. (The method itself points to 

procedures in ASTM E2515 to determine PM 

emissions.) This method has provisions for both 

manually and automatically fueled room and central

wood heaters, but does not cover masonry heaters or 

fireplaces. The method applies to wood fuels and

biomass- and grain-based fuels, but not coal. Note: 

This method uses 4 different burn rate categories than 

the 4 burn rate categories used in Method 28WHH; 

but the burn rate categories in Method 28WHH must 

be used to certify to the 2020 forced-air furnace 

standard, with results reported per burn rate category.

Forced-air furnaces 

using a simple 

average lb/MMBtu 

output metric

Cordwood,

wood chips, 

sawdust, 

firelogs, wood 

and biomass 

pellets – must 

certify to fuel in 

user’s manual. 

Cordwood

specific gravity 

of 0.60 to 0.73 

(dry basis, 

various species) 

and a moisture 

content of 18 to 

28% (dry basis).

PM emissions are 

to be measured by 

the dilution tunnel 

method specified 

in ASTM E2515-

11. Thermal 

efficiency (stack 

loss method) and 

CO emissions 

(dilution tunnel 

method) are 

measured using 

CSA B415.1-10.
14

Table 2. Descriptions of Test Methods Prescribed in 2015 Residential Wood Heater NSPS

Test Method

Name Type - Description

Applicable Heating 

Devices & Metric

Allowable Fuel 

Species

Measurement 

Methods

Sampling & Analytical Test Methods used in Conjunction with Fueling & Operating Protocols under Subparts AAA & QQQQ

ASTM E2515-11 

Standard Test 

Method for 

Determination of 

Particulate Matter 

Emissions 

Collected by a 

Dilution Tunnel

Sampling & Analytical Measurement – This 

method is used for measuring PM emissions from 

wood heaters including all heaters regulated under 

this NSPS – adjustable and single burn rate wood 

stoves, pellet stoves, hydronic heaters and forced-air 

furnaces – as well as fireplaces and masonry heaters. 

The total flue-gas exhaust from the wood heater is 

collected along with ambient dilution air with a 

collection hood. Duplicate sampling trains are used to 

extract gas samples from the dilution tunnel for 

determination of PM concentrations. Each sample 

train has two glass fiber filters in series, although

Teflon membrane filters or Teflon-coated glass fiber 

filters may be used. Four-inch filters may be used. 

The NSPS also requires that the first hour of PM 

emissions for each test run be measured, using a 

separate filter in one of the two parallel trains.

PM measurement for 

all wood heaters

regulated under 

NSPS. Total PM 

emissions are 

measured in grams. 

Test results for the 

first hour must be 

reported separately 

and also included in 

the total PM 

emissions per run.

Any solid-fuel 

including all 

wood species

This is a dilution 

tunnel PM 

measurement 

method

CSA B415.1-10 

Performance 

Testing of Solidfuel-burning 

Heating Appliances

Sampling & Analytical Measurement – This 

Canadian Standard includes methods for measuring 

heat outputs, appliance efficiencies, and CO emission 

levels from wood heaters. The method references 

other methods including ASTM E2515, ASTM 

E2618, and EPA Methods 1, 2, 5G, 28, 28A. The 

NSPS requires that the burn rates specified in Method 

28WHH must be used for hydronic heaters and for 

the 2020 forced-air furnace standard. CO is measured 

every 10 minutes during the test run.

CO measurement, 

thermal efficiency & 

heat output for all 

wood heaters

regulated under 

NSPS. CO emissions

are measured in 

grams, thermal 

efficiency is a 

percentage (%); and 

heat output is 

measured in MJ 

(converted to Btu)

Any wood 

species, density 

or moisture 

content allowed 

by fueling & 

operating 

protocols (listed 

above), 

including 

Douglas fir 

“crib”

dimensional 

lumber

CO emissions are 

measured via the 

dilution tunnel 

method. Thermal 

efficiency is based 

on the stack loss 

method.
15

3.3 Transition from the 1988 Crib Wood based NSPS to Cordwood

The pros of crib wood-based testing. Fuel characteristics and loading arrangements affect PM 

emissions from wood heaters. To provide a common basis for comparing emission performance 

among wood heaters for certification testing purposes, the EPA prescribed a standardized wood 

fuel as well as a standardized wood loading procedure in Method 28 for the 1988 NSPS. “Crib 

wood” is a specified configuration and quality of Douglas Fir dimensional lumber and spacers, 

which was intended to improve the repeatability of the test method in 1988. “Cordwood” is a 

different specified configuration and quality of wood that more closely resembles what a typical 

homeowner would use. In 1988, the EPA deemed the repeatability concerns of the test method 

underlying certification to favor the use of crib wood over cordwood. It was reasoned that 

cordwood testing would have caused greater variability and, thereby, would have been 

problematic as the basis of a certification program.

The pros of cordwood-based testing and the transition to cordwood-based requirements. While 

dimensional lumber creates a standardized fuel charge, it is not reflective of the type of fuel used 

in homes. One of the critical variables of testing is the air flow and air-to-fuel surface ratio. This 

standardized crib has allowed manufacturers to adjust the air flow to minimize emissions during 

certification testing. The adjusted air flow for cribs has the potential to decrease emissions 

performance with cordwood, which has a different physical configuration, and therefore the air 

flow through the unit will be considerably different with cordwood. Based on that hypothesis, 

many believe that use of cordwood for emissions testing is a better measure of how the heaters 

will perform in homes. Finally, some data suggest the repeatability of cribs is no better than 

cordwood, as indicated by hydronic heater and forced-air furnace tests conducted by 

Environment Canada.24

The EPA’s intention at the time of the 2014 NSPS proposal was to transition to cordwood as the 

basis for certification. Public comment on this issue in 2014 ranged from complete support for 

the proposed cordwood testing requirements to complete opposition to requiring cordwood

testing. Nonetheless, as noted above, stakeholders overwhelmingly agreed that tuning heaters for 

crib wood certification tests often results in poorer performance in homes. As Dr. James E. 

Houck has stated “Wood heaters, out of practical commercial necessity, are designed for optimal 

performance with NSPS test conditions.”

25 Recognizing this, the 2014 NSPS proposal required 

testing with cordwood for compliance with the 2020 Step 2 emissions limits based on: (1) the 

existence of a viable draft cordwood test method and the expectation that the ASTM test method 

for wood stoves using cordwood would be complete soon after the NSPS proposal; and (2) that 

significant testing of wood heaters adjusted (“re-tuned”) to perform well on cordwood would 

occur before promulgation of the 2015 final rule. In that final rule, the EPA continued to

encourage manufacturers to design wood heaters that best represent in-home performance on 

cordwood that consumers use. However, the ASTM cordwood test method was not completed in 

time for the 2015 final rule and only limited testing using the draft methods occurred.

In addition, the EPA received numerous comments from noncatalytic stove manufacturers,

laboratories and some states with concerns about when the cordwood test methods would be 

ready and how quickly noncatalytic stoves could be redesigned to perform well with cordwood

certification testing (that the Agency proposed for Step 2 in 2020, i.e., 5 years after the rule’s 

effective date). As the EPA discussed in the 2014 Notice of Data Availability (NODA), by May 

2014 the Agency had test data for three catalytic or hybrid wood heaters/stoves that performed 
16

very well on cordwood. However, considering all of the above, the Agency determined that it 

was premature to set a cordwood-based emission limit because it did not have sufficient data (in 

2014-2015) to support a regulatory requirement for cordwood testing (except for forced-air 

furnaces for which CSA B415.1–10 already specifies cordwood as the test fuel). Instead, the 

EPA provided an alternative compliance option (not a requirement) based on cordwood.

In the 2015 NSPS final rule, the EPA expressed the expectation that many manufacturers would

choose the alternative cordwood compliance testing option so that consumers would have more 

opportunities to purchase stoves that are tuned for in-home use. The Agency noted that many 

public comments indicated a critical need for test methods that reflect in-home use with 

cordwood, cold starts, cycling, moisture, heat demand and shorter averaging periods. It should be 

noted that the 2015 NSPS did provide cordwood test methods for hydronic heater and forced-airfurnaces; however, while these tests do use cordwood, they do not provide emission data on 

many of the operational parameters requested by commenters. The EPA stated strong agreement 

with these needs and noted that the Agency would consider alternative cordwood test method 

requests on a case-by-case basis until convinced that improved test methods have been 

sufficiently demonstrated that they can be relied upon for regulatory purposes. 

The EPA also stated in the 2015 NSPS preamble (section V.F. Test Methods) that for the time 

being it would be receptive to alternative test method requests that use the current ASTM draft 

cordwood method for wood stoves (“Standard Test Method for Determining Particulate Matter 

Emissions from Wood Heaters using Cordwood Test Fuel”). The Agency noted that the draft 

ASTM test method was sufficient to be used, upon request, for the cordwood alternative 

compliance option until better test methods could be developed. The EPA furthermore stated that 

it would be receptive to other alternative method requests that are sufficiently demonstrated, 

ideally using the EPA Method 301 validation procedures. The Agency pointed out that there are 

some manufacturers who already achieve the cordwood emission level and many more 

manufacturers were expected to take this option and submit data that would inform development 

of a required cordwood certification test in a future rulemaking. The EPA expressed hope that 

enough cordwood test data would be submitted within the next few years to enable the Agency to

establish revised certification requirements based on cordwood testing.

Test methods based on cordwood for wood stoves and central heaters, that were developed in the 

U.S. as well as other countries, are listed in the Appendix tables. These tables compare various 

parameters of each method listed.

3.4 What We Know About In-Home Device Use

It is widely recognized by stakeholders that the current test method fueling protocols for 

certification do not reflect the range of in-home device use, not merely due to the use of crib 

wood instead of cordwood, but also related to the variability in other fuel properties and 

operational parameters. James Houck, Lyrik Pitzman, and Paul Tiegs summarized some of the 

reasons for this in 2008:26

Due to the large number of variables associated with residential wood heaters and their 

operation, all common operational scenarios could not be incorporated into the testing 

procedures. In addition, the need for reproducibility in the certification methods 

necessitated divergence from some real-world operational scenarios. Finally, due to the 

paucity of relevant data prior to the 1988 promulgation of standards, some aspects of 
17

the testing methods do not simulate the real-world usage as well as they could based on 

our current understanding. The net effect of these issues is that while the NSPS for 

wood heaters, did and continues to, provide a commercial and regulatory expediency 

for the issue of air emissions from wood heaters, the emission data generated do not 

predict actual emission factors well and the certification methods could be refined 

considerably to allow for a more realistic target around which new technology wood 

heaters could be designed.... Regional differences due to climate and sociodemographic factors which include such parameter as burn rates, hot versus cold 

starts, wood moisture content, hardwood versus softwood fuel, the age distribution of 

wood heaters, and the level of reliance on wood heaters (main heat source vs. 

secondary heat source) can all cause differences in emission factors from region to 

region.

All stakeholders, including industry, have noted that certification values do not correlate well 

with in-home performance of wood heaters. As noted earlier, HPBA, NESCAUM and WESTAR 

have jointly recommended that “wood heater emission limits should be based on tests that 

correlate better with actual in-use emissions than the current test. There is a common interest 

among the parties to transition from the current crib-based wood heater certification test to a 

cordwood-based certification test...”27 The most significant problem with the certification test 

methods not reflecting the range of in-home fueling and operation is that manufacturers design 

and adjust their wood heaters to the test method in order to pass the applicable certification test;

but emissions may be higher when placed in operation. It should be noted that this is different 

than other stationary source rules, where additional emission reductions can be obtained at a later 

date when modifications are made. This is a natural consequence of regulating with a laboratory 

certification test and underscores the far-reaching importance of the test methods. 

Improved certification test methods could not only better predict actual emissions, but also drive 

the industry to design and adjust (“tune”) their wood heaters to perform well (i.e., emit less PM 

and burn more efficiently) in homes across the country, rather than primarily in the test 

laboratory. As NESCAUM has stated, “The use of appropriate test methods that challenge a unit 

to perform its best under a variety of conditions is critical to ensuring clean burning units in field 

operations.”28 Fueling protocol test methods more reflective of in-home device use would 

thereby better protect human health and the environment and also move the state of the science 

in the direction of cleaner devices.

Thus, it is important to catalog what we know about in-home device use. The following list 

includes aspects of in-home wood heater use that improved fueling protocols should address:

 Fuel species, fuel density and fuel moisture of the cordwood (not crib wood) used in 

wood heaters vary greatly from region-to-region and consumer-to-consumer and can 

impact emissions significantly;

 Consumer operation of wood heaters at low burn rates may be more common than is 

currently represented in the fueling protocol weighting schemes. Low burn rates result in 

higher PM per mass of wood burned (emission factors), while high burn rates can result 

in higher stack rates (emission rates). This means that emissions at the lowest and highest 

burn rates tend to be the most problematic, rather than emissions at the middle burn rates;
18

 Consumers often overload fireboxes, beyond what is ideal for efficient and loweremitting burning. This overloading is not captured by most fueling protocols; and

 High-level, short-term PM emissions from wood heaters (i.e., during start-up and re-fuel) 

are not captured by the current test methods which average emissions over a full fuel 

charge.

3.5 Capturing Fuel Species Variability including Moisture Content

Fuel species and density. The type of fuel species used by consumers varies from region to 

region of the country, based on the wood species most prevalent in each region. Deciduous 

hardwoods such as oak, maple, hickory and birch dominate wood fuel in the Eastern and 

Midwestern U.S. Evergreen softwoods such as Douglas Fir and various pine species dominate 

wood fuel in the Western U.S., although hardwoods are also common fuel in the West. 

NESCAUM has claimed that for the country overall there is “a 50-50 split between softwood and 

hardwood burners”, based on formal and informal surveys.29

In general, hardwood provides longer burning fires, is denser, and contains more total heat per 

volume (cord) but less total heat per unit of mass compared to softwood; while softwood, 

although less dense, has a higher heat content per unit of mass because it contains more resin 

than hardwood.30 NESCAUM has claimed that the use of oak as the test fuel for hydronic heaters 

can significantly underestimate emissions compared to other, less dense woods.31 In one study, 

testing data indicates that emission rates from hydronic heaters are 200% to 500% greater for 

softwoods than hardwoods.32

For wood stoves, studies are conflicted regarding which wood species provides the cleaner burn. 

This may be related to differences in the moisture content and/or the density of the wood fuel 

used in the studies (that can vary for a given species). The exact difference that wood (tree) 

species makes in certification testing is unknown; therefore, regulators cannot yet have an 

informed opinion regarding whether or not the manufacturer should be allowed to choose the 

species used in certification testing. Consequently, NESCAUM has suggested that EPA adopt a 

single cordwood fuel type with specified allowable species and densities, for testing all 

residential wood heater devices, and furthermore that the fuel density be reported in all test 

reports.33

In order to better reflect in-home device use, it is important for the certification test methods to 

represent the range of fuel species and densities used across the country, while still maintaining a 

level playing field for comparing emissions across devices. How this can be accomplished –

through prescribing fuel species and densities across devices, or through merely requiring that 

the density of the test fuel be reported – needs to be analyzed further.

Moisture content of wood fuel. The moisture content of wood fuel should not be confused with 

laboratory terms such as “dry wood” and “wet wood”, which are constructs used in developing 

AP-42 emission factors. These terms refer to the use of a mathematical operation to remove the 

weight of moisture in the fuel (or not), so that all tests are on an equal basis.34 Consumers, 

however, more commonly understand the terms “dry wood” and “wet wood” in terms of 

moisture content and its effect on combustion. 
19

Moisture content refers to the percentage of moisture in the wood fuel, reported either as a dry 

basis (db) or wet basis (wb). The dry basis moisture content is determined by dividing the weight 

of the water in the wood fuel by the weight of the dry wood, while the wet basis moisture content

is the weight of the water in the wood fuel divided by the total weight of the wood including the 

water weight. When comparing the moisture content of wood fuel it is important to use a 

consistent metric. For certification methods, the basis of the moisture content is explicitly 

defined as either dry basis or wet basis.

Both wood with very low moisture content and wood with very high moisture content produce 

higher PM emissions compared to wood fuel with a moisture content near the center of the range 

(approximately 15-25 percent).35 The technical reasons for this were understood and explained 

by experts in wood heater combustion in the 1980’s:

Higher moisture contents increase the amount of heat required to dry the fuel. This in 

turn lowers the firebox temperature, increasing particulate and CO emissions. 

Conversely, very low moisture levels ... can also increase emissions because volatile 

fuel gases are generated at a faster rate than they can be efficiently combusted.36

However, for in-home wood heater fueling, increased wood moisture generally results in 

substantially increased PM emissions.37 The 2015 NSPS fueling protocol test methods require a 

moisture content range beginning from a low of between 15 and 19 percent and extending to a 

maximum of 25 percent. In addition, the 2015 NSPS prohibits consumers from using wood fuel 

with a moisture content of greater than 20 percent.

Moisture content varies not only according to variations in consumer behavior regarding the 

degree to which the wood is seasoned (dried), but also according to wood species. Seasoned 

hardwoods (such as oak) have a higher moisture content than seasoned softwoods (such as pine). 

Because of the closed cell nature of hardwoods compared to softwoods, hardwoods take longer 

to season than do softwoods – and in fact, may never dry out as much as softwoods do. 

Consequently, hardwood is often burned wetter than softwood.38

Furthermore, some states have concerns that the current methods used to measure moisture 

content are not robust enough to be accurate for especially hardwood fuels such as oak, given the 

difficulty in obtaining uniform moisture content throughout the fuel piece.39 Obtaining an 

accurate measure of moisture content is important because moisture content affects the 

variability of measured PM emissions in the test methods. How to better reflect the range of 

actual (in-home use) moisture content in the certification test methods, while at the same time 

reducing unnecessary variability, needs to be discussed further.

3.6 Capturing Variability in Burn Rates, Firebox Load and Start-up

Burn rate. Burn rate means the rate at which wood fuel is consumed in a wood stove, as 

expressed in units such as kg/hr or lb/hr. Lower burn rates cause more PM emissions for a given 

amount of fuel (a higher emission factor). It is has long been known and is widely accepted that 

increased burn rates result in lower PM emission factors (g/kg PM on probe and filter catch) and 

lower CO emissions as well.40 PM emissions measured by using the EPA Method 28 protocol are 

calculated by a prescribed weighting of the probabilities of national burn rates. Houck has noted

that “As a consequence of this weighting scheme, emissions at low burn rates represent only a 

fraction of the calculated weighted certification emission values yet they can be expected to 
20

represent a larger fraction of the wood heater use in [climates requiring relatively fewer high/hot 

burns]...”41 NESCAUM has stated that “It is vital that all residential wood heating devices be 

tested at their lowest burn setting and that they be manufactured to permanently prevent 

alteration of this low burn setting.”42 On the other hand, while emission factors (PM for a given 

amount of fuel) are lower at higher burn rates, the emission rate (PM over a given time period) 

can be higher at the high burn rate for some devices, due to the emission factor decreasing 

proportionally less than the fuel consumption increase.

Arguably, improved certification test methods need to focus more on emissions at low and high 

burn rates to better reflect the range of wood heater burning and emissions around the country, 

and to focus more on burn rates during which emissions are highest. NESCAUM points to EPA’s 

2009 Stack Testing Policy (at http://www3.epa.gov/ttnemc01/guidlnd/gd-050.pdf) and asserts 

that the policy requires a test method that captures the highest emission rate under normal (inhome use) operating conditions and allows for determination of whether compliance with the 

emission limit is continuous, not intermittent based on averaging.43 Stakeholders such as 

NESCAUM commented on the 2014 NSPS proposal that they favored certification emission 

values based on the low (Method 28 Category 1) burn rate and high (Method 28 Category 4) 

burn rate, with two more runs repeated at the burn rate with the highest PM emissions.44 This 

would capture emissions at the most polluting (worst case) burn rate and would improve 

precision at this burn rate. Whether future certified emission value(s) for wood stoves should be 

based on worst case emissions at either the low or high burn rates, or be based on a weighted 

average, requires further discussion. 

For hydronic heaters, the categories in EPA Method 28 WHH are based on a heat load demand 

(in Btu/hr) rather than a burn rate. Some stakeholders, such as NESCAUM, maintain that the 

heat load categories in Method 28 WHH do not reflect typical heat load patterns and that 

certification emission levels based on these categories in the test method lead to an 

underestimation of emission levels compared to actual (in-home use) emissions.45 For the indepth hydronic heater study prepared for NYSERDA, experts used a duty cycle or “call for heat” 

load pattern based on a simulation program for heat demand typical of homes in Syracuse, NY – 

also known as the “Syracuse load profile”.46 NESCAUM has suggested that using an emission 

profile such as the Syracuse load profile used in EPA Office of Research and Development’s

analysis of hydronic heater emissions instead of Method 28 WHH’s heat load categories would 

be more reflective of in-home device use and thereby more protective of people exposed to 

hydronic heater emissions, such as neighbors.47 In addition, research has shown that oversizing 

of hydronic heaters causes the devices to spend more time idling, with dampers closed, which 

decreases efficiency and increases PM emissions.48 (Thermal storage capability in hydronic 

heaters improves these performance problems of oversized units.) Continued discussion is 

needed regarding using load patterns more typical of in-home device use than is currently 

prescribed in Method 28 WHH’s fueling and operating protocol. 

Wood load amount in firebox. Completely filling the firebox of a wood heater is considered 

overloading it, compared to ideal operation, and causes lower combustion efficiency with higher 

PM emissions.49 It was established by the 1980s that PM emissions increase significantly with 

greater fuel loading density – that is, with greater mass of wood per unit firebox volume.50 In 

general, smaller more frequent loads emit less PM than large loads – that is, smaller loads 

generate lower emissions in the same stove at the same burn rate.51
21

Some studies suggest that the wood load amount may have a more significant effect on PM 

emission rates (not necessarily emission factors) than burn rate. This is because the higher stack 

flow rates at higher burn rates (which have lower g/kg PM emission factors) and the lower stack 

flow rates at lower burn rates (which have higher g/kg PM emission factors) tend to 

counterbalance each other with respect to (g/hr) PM emission rates.52

With respect to consumer behavior, it is known that consumers often load up their wood heaters 

with as much fuel as feasible, in order to maximize burning times between reloading and thereby 

minimize stove-tending labor. This is especially true of overnight burns, in which wood heaters 

are loaded to the max and air flow is temporarily increased to create a high burn before closing 

down dampers to create a very low, smoldering burn with a full wood load overnight and ensure 

hot embers in the morning. This low burn rate coupled with the large fuel load amount results in 

significantly increased emissions.

Improved fueling protocols need to better reflect the range of consumer behavior regarding wood 

loading amounts. The currently prescribed test fuel loading densities in the fueling protocols may 

not represent the range of wood loading amounts typical of consumers, especially with regard to 

overloading of fireboxes. 

Start-up and refueling emissions. Start-up (“cold-start”) of wood heaters result in a 

disproportionate and large amount of PM emissions from all stoves, including notably some that 

are relatively clean burning at higher temperatures, like catalytic stoves (e.g., if the catalyst is 

bypassed because it hasn’t yet heated up to operating temperature).53 Start-up emissions vary 

from region-to-region and consumer-to-consumer, but some of the highest emission rates 

typically occur during start-up. More cold starts can be expected in mild climates compared to 

colder climates because in cold climates wood stoves may be burning around the clock, with at 

least hot embers ever-present in the fire box to avoid cold starts. On the other hand, many 

consumers even in cold climates use their wood heaters as a supplemental heat source rather than 

a primary heat source – in which case cold-starts are more frequent. NESCAUM has argued that, 

based on actual monitoring of stack temperatures, there are typically two cold starts per day for 

wood stoves; therefore peak emissions rates for wood stoves are occurring 2 to 4 times per day.54

Similar to start-up emissions, emissions during refueling are problematic especially for hydronic 

heaters. NESCAUM notes that high-level, short-term PM emissions are not sufficiently captured 

by current test methods:

The current test method does not capture these spikes because it averages emissions 

over a full fuel charge. These can last from 2 to 40+ hours and include in the average 

what is referred to as the “charcoal tail” (a long period where the unit operates at very 

low emissions). As a result, the current test procedure does not adequately capture high 

emissions that can occur immediately after refueling a unit.55

This problem is also seen in wood stove testing, where it is estimated that ~30% of the testing 

time is needed to burn the last 10% of the fuel charge. Regarding the test methods, a “hot to hot”

test means that emissions are measured starting when fuel is placed on a hot coal bed and the test 

is ended while the coal bed is still hot. Incorporating start-up conditions could use two methods: 

a “cold to hot” test or a separate start up test protocol. A “cold to hot” test means that emissions 

are measured starting when no coal bed exists and ends when the second steady state fuel charge 

has been completely combusted. Alternatively, a separate emissions test could be conducted to 
22

measure emissions from the starting of the fire until the unit is ready to be reloaded for a steady 

state test.

It is important that the certification test method takes into account start-up and refueling 

emissions, in order to recognize wood heaters that perform well under these conditions from 

those that do not. By measuring emissions throughout a device’s duty cycle, EPA can ensure 

cleaner operation during in-home use and also recognize those devices that have invested in new 

technology and design. How exactly the fueling protocol and emissions calculations should be 

revised in order to better capture start-up and refueling emissions is a matter for further 

discussion.
23

4.0 EPA’s Process for Approving Alternative Test 

Methods Allowed Under the Current NSPS

This section discusses the EPA’s process for reviewing and approving case-by-case alternative 

test method requests, how the EPA receives input on alternative test method approvals, and 

EPA’s approval of broadly applicable alternative test methods.

4.1 Case-by-Case Alternative Test Method Approval

EPA’s process for approval of alternatives and modifications to test methods and testing 

procedures is outlined in Guideline Document GD-022, available on the internet at:

http://www3.epa.gov/ttnemc01/guidlnd/gd22.pdf.

The General Provisions to 40 CFR Parts 60, 61 and 63 (NSPS and NESHAP, Sections 

60.8(b)(2), 61.13 (h)(1)(ii), and 63.7(e)(2)(ii)) provide the EPA Administrator with the authority 

to approve alternatives or changes to test methods, specified in the subparts to these CFR parts, 

for determining compliance of stationary sources with these Federal emission limitations or 

standards. The authority for approval of major alternatives to methods can be delegated only 

within the Office of Air and Radiation (OAR). Within OAR, the authority for approval of major 

changes to test methods has been delegated down through the Office of Air Quality Planning and 

Analysis (OAQPS) to the Leader of the Measurement Technology Group in the Air Quality 

Analysis Division. In addition, the 2015 NSPS states in sections 60.539(a) and 60.5482 that 

EPA will not delegate the authority of the establishment or revision of test methods.

The Measurement Technology Group undertakes a rigorous review of each alternative test 

method request, with a focus on making a technical determination that the requested alternative 

test method will provide results adequate for the EPA Administrator’s determination of 

compliance and that the proposed change in the test method will not negatively affect the 

stringency of the applicable regulation.

A party wishing to comply with a rule in Part 60, 61, or 63 using an alternative test method 

approach must provide sufficient evidence demonstrating that the alternative test method is 

needed in their instance. Examples of such supporting reasons may be: 1) that there are concerns 

regarding interferences or biases to the rule-prescribed testing approach and/or 2) that allowing 

for new technology or testing approaches allows for improved accuracy and/or lower costs 

and/or 3) that allowing alternative measurement locations for hybrid processes or processes 

subject to multiple regulations might be measured more appropriately with alternate means.

Approval of an alternative test method application is based on substantive review of technical 

supporting information and/or data. Examples of such information include: 1) direct comparisons 

with existing reference or compliance test methods (e.g. Method 301 comparison data), 2) 

precision and bias determinations of the proposed approach and detailed test procedures and 3) 

data quality objectives of the proposed approach. 

An alternative test method application may be rejected, or approved with modifications, or 

approved as submitted, depending on the findings of the technical review. Rejected applications 
24

may be re-worked and re-submitted if appropriate. Tests conducted with an approved alternative 

test method must be conducted according to the procedures listed in the approval letter. 

Requests of these types are typically approved on an individual basis (in this case, for use by a 

specific wood heater), though on occasion where it is deemed appropriate by review, the request 

may be approved for use on a broader basis (e.g. source category-wide or, in this case, for more 

than just the specific heater referred to in the application), as explained further in Section 4.3.

4.2 Process for EPA to Receive Input on Alternative Test Methods

Like rulemaking, the review of an alternative test method request by the EPA Administrator’s 

delegated authority and his/her technical staff is an inherently governmental process. Once a sitespecific (heater-specific) or broadly applicable alternative test method approval is made available 

for use, members of industry or the general public may send the EPA comments at any time, 

providing information and opinion about the details and measurement appropriateness of a 

specific test approach. (See 72 FR 4257, 1/30/2007, regarding the EPA’s decision and plan to 

issue broadly applicable alternative test method approvals, available at: 

http://www3.epa.gov/ttn/emc/approalt/FRNotc.pdf.) Where substantial data driven examples 

are made available, the EPA may undertake an additional technical review of an existing 

alternative test method and modify or withdraw that test method if the technical justification to 

do so is sufficient. 

It must be noted that any time the EPA reviews an alternative test method request, the same 

principles listed above would apply. The alternative test method must continue to provide results 

adequate for the EPA Administrator’s determination of compliance and the proposed change in 

the test method must not negatively affect the stringency of the applicable regulation.

4.3 Broadly Applicable Alternative Test Method Approval

Where the EPA’s Measurement Technology Group finds that it is appropriate to allow an 

alternative test method for compliance determinations on a broader basis, a public posting of the 

Broadly Applicable Alternate is made available here: 

http://www3.epa.gov/ttn/emc/approalt.html. Additionally, an annual notice that summarizes 

all such broadly applicable alternative test methods approved during the previous calendar year 

is published in the Federal Register each spring.

Note that when an alternative test method has been found to be appropriate for use as a Broadly 

Applicable Alternative Test Method, the EPA may include modifications in the approval notice 

that must be followed each time the alternative test method is used. 

Alternative test method approvals are also subject to withdrawal. The EPA may list a “sunset 

date” in the original approval, or the Agency may withdraw an approval, for cause, at any date in 

the future. Such instances may be when rule compliance requirements change rendering the 

alternative test method obsolete for the purposes of compliance determination, or when other 

technologies appropriate for determining compliance become cost effective and continue to 

provide equal or superior data quality.
25

Device manufacturers or testing laboratories may voluntarily choose to use these broadly 

applicable alternative test methods. Use of these alternatives does not change the applicable 

emission standards.
26

5.0 EPA Reference Test Method Development

This section discusses the meaning of an EPA reference method in general, the currently 

available reference test methods for residential wood heaters specifically, and the process for 

adopting a new EPA reference test method.

5.1 What is an EPA Reference Test Method?

The term ‘‘reference method’’ is used in 40 CFR parts 60 and 61 instead of the term ‘‘test 

method’’ which is used in 40 CFR part 63. In 40 CFR part 60, reference method means “any 

method of sampling and analyzing for an air pollutant as specified in the applicable subpart.”

The definition in 40 CFR part 61 is similar. For simplicity, we use the term ‘‘test method’’ in this 

paper to refer to both ‘‘test methods’’ under 40 CFR part 63 and ‘‘reference methods’’ under 40 

CFR parts 60 and 61. Citations and definitions in all three of these parts refer to the use of 

alternatives to test (or reference) methods. The EPA maintains a list of promulgated reference 

test methods applicable to stationary source emissions that is available at: 

http://www3.epa.gov/ttnemc01/promgate.html. 

The EPA’s rules and regulations may also refer to test methods not promulgated by the EPA but 

rather established by a voluntary consensus standard, such as ASTM test methods. 

5.2 What are the EPA Reference Test Methods for Wood Heaters?

40 CFR 60, Subpart AAA lists the following test methods for particulate emissions compliance 

demonstration (for adjustable and single burn rate wood stoves and pellet stoves):

Crib wood:

Method 28R of 40 CFR 60, Appendix A-8, or

ASTM E2779-10,

Both of these fueling protocols use ASTM E2515-11 for PM determination

Cordwood:

An EPA approved alternative test method based on Draft ASTM Cordwood Test 

Method WK47329 (fueling protocol), using ASTME2515-11 for PM 

determination.

40 CFR 60, Subpart QQQQ lists the following test methods for particulate emissions compliance 

demonstration (for hydronic heaters and forced-air furnaces):

Crib wood:

Method 28WHH of 40 CFR 60, Appendix A-8 (for hydronic heaters), or

ASTM E2618-13 (for hydronic heaters) 

Both of these fueling protocols use ASTM E2515-11 for PM determination

Cordwood:

Method 28WHH-PTS of 40 CFR 60, Appendix A-8 (for hydronic heaters), or

CSA B415.1-10 (for forced-air furnaces),

Both of these fueling protocols use ASTM E2515-11 for PM determination, or

EN 303-5 (for hydronic heaters at 2015 Step 1 only), or 

An EPA approved alternative test method using ASTM E2515-11 for PM 

determination.
27

5.3 Process for Adopting a New EPA Reference Test Method

The EPA’s process for development of new test methodology involves several steps. Initially a 

review of existing test methodology is conducted and target criteria are identified to provide Data 

Quality Objectives for the test method once completed. The EPA then engages stakeholders in 

open discussion regarding potential testing approaches, including a request for outside 

information and data, and feedback on draft methods prior to proposal (likely two or three 

iterations). 

The EPA then assembles the method for proposal based on feedback from the most recent draft 

and any recently collected data. This begins the formal “Notice and Comment” review of the test 

method where the EPA publishes the proposed method in the Federal Register and opens a 

public docket to collect public information, comment, and additional data if made available. At 

the end of the comment period, the EPA reviews all comments submitted and drafts a response to 

substantive comments along with a final version of the test method. The final test method is then 

promulgated through publication in the Federal Register and the test method is available for use. 

For more information about EPA’s Data Quality Objectives process see:

http://www3.epa.gov/epawaste/hazard/correctiveaction/resources/guidance/qa/epaqag4.pdf.

Once established as a promulgated test method, a new EPA test method can be requested as an 

alternative to an existing test method for use in meeting the requirements of a regulation, 

provided that it meets the alternative test method technical review requirements previously 

discussed in Section 4. Additionally, it may be incorporated into other EPA regulations, such as 

Subpart AAA through notice and comment rulemaking (as just described).

Fueling protocol. Creation and adaptation of a revised or new fueling protocol for crib wood or 

cordwood will follow a similar process to development of a new sampling/analytical test method,

as described above.
28

6.0 Process for Improving Cordwood Test Methods 

As mentioned earlier, it is a common goal of stakeholders that test methods transition from a 

crib-based certification test to a cordwood test. This section summarizes the goals, structures and 

process for identifying robust cordwood test method(s). The goal of this process is the 

development of an EPA reference test method for residential wood heaters that uses cordwood

rather than dimensional (“crib wood”) lumber as the test fuel, more accurately representing inhome use emissions and improving testing reliability. The process must meet regulatory needs,

as well as understand industry concerns. The EPA believes that this is a reasonable approach to 

further the science and to develop cordwood methods that reflect in-home use, improve the 

precision of wood stove testing, and be protective of human health and the environment as the 

cornerstone of the NSPS certification program.

To achieve this goal, a multi-tier process is envisioned by state regulators that consists of a 

Steering Committee and two Technical Workgroups. The Technical Workgroups will identify 

data needs, obtain and review data, and develop recommendations. The Steering Committee will 

provide oversight, develop guidelines, and review and adopt recommendations from the 

Technical Workgroups. The state MJO’s will take a lead role in this process, with the EPA 

participating in an advisory role to communicate the types of information required to revise EPA 

reference test methods.

6.1 Steering Committee Process

The primary role of the Steering Committee is to develop test method evaluation guidelines and

prepare a paper that presents recommendations, and, if applicable, incorporates dissenting 

opinions. The Steering Committee will develop a framework to guide the work of Technical 

Workgroups, provide feedback/prioritization on Technical Workgroup recommendations, 

determine preferred methods, and compile the findings of this effort. Ideally, the Technical 

Workgroups will report quarterly to the Steering Committee on their efforts, and more frequently 

when necessary. The Steering Committee will be responsible for presenting recommendations 

for consideration by the EPA. 

Membership in the Steering Committee is comprised of staff with legal and regulatory expertise, 

representing the needs of state and local regulatory authorities. The Steering Committee is led by 

the multi-jurisdiction organizations (MJOs) participating in this effort. The MJOs are responsible 

for convening the Committee, developing agendas, facilitating meetings, and documenting 

outcomes. Core membership in the Steering Committee has been identified and additional 

members will be considered upon request.

The core membership of the Steering Committee consists of NESCAUM, WESTAR, and state 

regulators from Washington state, Massachusetts, Vermont and Alaska. One of the first efforts of 

the Steering Committee was to develop a timeline and to begin drafting a framework for the 

Technical Workgroup process. Draft elements are identified below.
29

6.1.1 Timeline

The core Steering Committee established a proposed timeline for the cordwood test method 

development process. The goal is to have the first Steering Committee meeting in the summer of 

2016. The major milestones are:

 Spring 2016 - Discussion Paper: The paper (this document) outlines major themes and 

their key criteria. The major themes are fueling and appliance operation protocol and 

measurement method improvements. The key criteria were developed by the Steering 

Committee, as outlined in Section 6.1.3. This Discussion Paper will also serve to further 

open these topics for input from any party.

 Spring of 2016 – Form Technical Workgroups: The Steering Committee plans to form 

Technical Workgroups by the spring of 2016. The two groups will be a PM Measurement 

Method Workgroup and a Fueling/Operational Protocol Workgroup.

 Summer/Fall 2016 – Develop Process and Data Needs: The Technical Workgroups will 

develop and present recommendations on their respective processes, the technical 

questions that they will address, and their data needs. Outreach to stakeholders will be a 

joint effort of the Technical Workgroups and Steering Committee.

 2017-2018 – Technical Workgroups’ Review of Methods: As data become available and 

analyses are conducted, the Technical Workgroups will review and draft comments on 

their respective technical questions. This information will be presented to the Steering 

Committee at quarterly meetings. The Technical Workgroups may request that the EPA 

conduct research on specific questions for which the data are limited.

 Summer 2018 – Wrap-up: The Steering Committee will compile the conclusions of the 

Technical Workgroups. Alternative options and opinions will be provided. 

The EPA will review the information provided by the Steering Committee and the Technical 

Workgroups and will determine whether it has sufficient basis to propose an EPA reference test 

method based on cordwood. There is no timeline for any future regulations.

6.1.2 Steering Committee’s Charge to the Technical Workgroups

The core Steering Committee identified five areas of focus for the Technical Workgroups 

including: 

o Identify criteria to guide test method recommendations;

o Determine which processes and associated data are needed to ensure that emissions 

measurements are based on an equivalent or more stringent method; 

o Select and prioritize devices for cordwood test method acceptance;

o Develop a formal timeline for submitting test methods for consideration; and

o Define documentation requirements for review.

Key Criteria. An initial list of parameters and variables that will need to be considered by the 

Technical Workgroups is provided in Table 3. This list is meant to create a starting point for a 

discussion with the Technical Workgroups. 
30

The Workgroups and the Steering Committee will refine the preliminary list of key criteria and 

finalize in the summer of 2016. Additionally, Steering Committee members will attempt to 

identify potential funding sources to allow independent research to be conducted to inform this 

process. If successful in obtaining funds, the Steering Committee will direct the Technical 

Workgroups to draft priority items to be researched with the available funds. The research 

priorities will be reviewed and modified or approved by the Steering Committee. The Technical 

Workgroups will also assist in designing research recommendations and other similar technical 

guidance as needed. The Technical Workgroups are discussed in more detail in the next section.

Table 3. Preliminary List of Key Criteria to be Considered for Cordwood Test Method

Criteria Description, Metric and Other Considerations

Device Type Identify units to test that demonstrate minimal variability due to design. Assure 

that variability is due to the method rather than the device.

Fueling

Cordwood species or density (to capture regional variabilities)

Cordwood piece sizing

Cordwood piece moisture

Loading configuration – standardized versus “chaotic”/in-home use

Loading amount – Owner Manual’s instructions versus more in-home use

Burn Periods

Start-up (SU) – cold start?

Steady State (SS) – refined further

Idling condition

Shut-down (SH)

Other Periods such as reload? Are the burn periods device-specific? (Note: 

Most methods include nominal or category 4 burns, which may be an important 

linkage to past data even if not a strong component of future testing.)

Operation 

during Burn 

Periods

Steady State versus Emission Profile (i.e., controls not touched under steady 

state versus allowing for and perhaps dictating controls to capture an emission 

profile); Scripted operation to represent common homeowner fueling practices

(e.g., should equipment settings be scripted to capture going quickly from a 

very high burn rate to a very low burn rate to simulate an overnight burn)? 

If scripted, how many runs at each setting (e.g., 4 scripts with 3 runs per script, 

for a total of 12 runs)? 

Representative 

Length of 

Burn Periods

Capture entire burn period or just portion of each key period? For scripted runs, 

how long at each setting (e.g., 2 to 3 hours of measurements for an 

“abbreviated batch run” to capture overnight smoldering emissions versus 

measuring during an entire overnight run) and what is the cost benefit analysis?

Adjustments 

during Burn 

Periods

Is raking of coal bed allowed?

Is poking of fuel allowed?

Is the door open or closed? When and how long?

Should owner’s manual dictate operation or not – should it instruct conditions 

on the test method?

Note: Cordwood burns in non-uniform patterns, sometimes forming arches that 

can collapse at odd intervals; accommodation is needed for this practical reality

Duration of 

Burn Period / 

Test Run

Should test runs have consistent definition of end and what should that 

definition be (e.g., when 90% of fuel is consumed in order to eliminate charcoal 

tail and minimize duration)?
31

Table 3. Preliminary List of Key Criteria to be Considered for Cordwood Test Method

Criteria Description, Metric and Other Considerations

Stack height

What stack height should be specified or allowed during testing?

(Note: Manufacturers stipulate stack heights for many devices to optimize 

performance. Testing heights should not be less than these heights unless there 

is evidence of lower stack heights in common field practice. This may have 

higher relevance to central heaters than room heaters.)

PM Emission 

Measurement

Burn period’s emission measurement: individual emission measurements for 

each burn cycle/category or a single (simple or weighted) average?

What PM should be measured (e.g., Total PM, Filterable PM, Condensable 

PM, 7-day versus immediate measurement, ambient or 40 degree PM)

What metric (e.g., average, typical, peak/maximum, sub-daily, daily, annual)

What units should be used for testing (e.g., g/hr, g/kg, g/MJ, lb/mmBtu)? 

Would the same metric apply across devices, including room heaters and 

central heaters? What is most helpful to consumers?

Precision / 

Repeatability*

Need to improve the precision and repeatability of the cordwood fueling 

protocol and PM emission measurements to improve confidence in the 

certification process and reduce cost and time to determine certification*

PM 

Measurement 

Method

Dilution tunnel issues including dilution ratio and residence time, semi-volatile 

loss, filter material (glass versus Teflon filters), filter temperature, relative 

humidity issues, alternative PM methods, characterizing method precision*

Pollutants What pollutants beyond PM should be measured (e.g., CO, NOx, VOC, PAH)

Efficiency

Measurement

How to provide usable efficiency for consumers (i.e., importance of level 

playing field). Note for example that currently hydronic heaters use thermal 

output to measure efficiency, while stack loss method is used to measure 

efficiency of forced-air furnaces.

Flexibility

The fueling protocol of the test method needs to be flexible enough to capture 

software settings, and to encourage smart devices without running risk of 

allowing evasive software settings during a test

Cost Importance of cost of conducting the test 

Ease Importance of ease of conducting the test (e.g., KISS principle)

Verification Importance of opportunities for outside verification of method

Transparency Importance of test method transparency

* Note: Regarding capturing variability, running the test method on a pellet stove and pellet boiler 

as the basis for a Method 301 comparison was suggested. This would minimize fueling variability 

and get at measurement variability in isolation. Then the comparison process could move up to a 

cordwood stove and boiler to start characterizing fueling variability.

6.2 Technical Workgroup Process

MJOs and state regulators plan to form two Technical Workgroups: (A) PM Measurement 

Workgroup and (B) Fueling/Operational Protocol Workgroup. The role of these workgroups is to 

develop recommendations to the Steering Committee based on the most recent science, and 

conduct an independent review of the data to develop recommendations for a preferred 
32

cordwood method pathway based on these findings. The workgroups will help refine criteria and 

review processes, identify data needs, conduct an independent review and develop 

recommendations that will be presented to the Steering Committee for consideration. Another 

important component of the Technical Workgroups’ charge will be to assist the Steering 

Committee in prioritizing testing with any funds that are available, helping with experimental 

design, etc., as outlined in Section 6.1.3. If needed, additional more-narrowly-focused technical 

workgroups might be formed to address specific topics. New workgroups may be created 

dependent on the availability of staff and/or resources to support these groups. The Technical 

Workgroups will be formed by invitation from the Steering Committee.

6.2.1 PM Measurement Method Workgroup

The PM Measurement Method Workgroup will address issues specifically related to PM 

measurement methods included in 5G, 5H and other alternative measurement methods 

referenced in the NSPS such as ASTM, CSA and EN measurement protocols, or other new 

methods. This workgroup may also provide feedback to the alternative test method process for 

sun-setting outdated measurement and fueling protocols. The Steering Committee will develop a 

list of potential participants in this workgroup. This workgroup will update the Steering 

Committee at least once per quarter. The Steering Committee will oversee all workgroup efforts. 

The following is a draft timeline for this process:

 Spring 2016 – Form PM Measurement Method Workgroup: The Committee will invite 

nominees to participate.

 Summer 2016 - Refine Research Topic Areas: Compile and review a list of PM 

measurement topics and further refine and modify this list. The group might also 

conduct literature reviews and reach out to industry, labs and researchers worldwide to 

determine if data exists to inform the review effort. Upon completion of this effort, the 

group will identify a prioritized list of research needs. The information completed under 

this effort will be presented to the Steering Committee as items are finalized.

 Fall 2016 - Develop Method Recommendations: The group will review existing data and 

literature and prepare recommendations for the Steering Committee to improve the 

capacity of PM measurement methods.

 Early 2017 – Wrap-up: The Technical Workgroups and Steering Committee will prepare 

materials for the EPA’s review and consideration, including elements for an EPA 

proposal for method improvements. 

6.2.2 Fueling/Operational Protocol Workgroup

The role of this workgroup is to review candidate cordwood methods, focusing primarily on the 

fueling and operational protocols. This workgroup will review individual methods and complete 

an assessment of each method submitted for review. Reviews will be based on the key criteria 

listed in Table 3. This workgroup will also provide technical guidance on test method fueling and 

operation issues as they are identified. This will involve a review of the preliminary criteria 

developed by this workgroup, as well as an assessment of available data and future data needs. 
33

This workgroup will update the Steering Committee at least once per quarter. The Steering 

Committee will oversee all workgroup efforts. The workgroup will prepare a recommendations 

paper for the Steering Committee that outlines the strengths and weaknesses of various methods 

and presents, if possible, a single recommended or preferred method for use in U.S. regulatory 

programs. If consensus is not reached on all or some items, these issues should be detailed in the 

recommendations report. 

This workgroup will be comprised of a small group of technical experts that may be chosen from 

a variety of entities including regulatory agencies, laboratories, industry, MJOs, or academia. 

Members should have expertise in test methods, unit operations, and PM measurement. The 

Steering Committee will develop a list of potential participants in this workgroup. 

The following is a draft timeline and outline for this workgroup:

 Spring 2016 - Form Fueling Protocol Workgroup: The Steering Committee will draft 

invitations and invite nominees to participate in the effort.

 Summer 2016 - Review and discuss framework: Convene the workgroup to further refine 

and define the Steering Committee’s framework. Meet with Steering Committee to 

discuss and adopt refinements. 

 Summer/Fall 2016 - Draft recommendations on data needs for comparative analysis: The 

workgroup should:

o Discuss and summarize data needs that are critical for completing a comparative 

review of test methods and present these findings to the Steering Committee;

o Identify research that must be completed prior to recommending a preferred 

method;

o Identify existing test methods that should be included in the review process; and

o Outline outreach efforts necessary to raise broad awareness of this effort. 

 May 2017 to May 2018 - Review and comment on methods: After the test method review 

criteria have been finalized and approved by the Steering Committee, the workgroup will 

review data and conduct a comparative analysis of various test methods as they are 

submitted for review by the Steering Committee.

 June 2018 - Draft recommendation and brief Steering Committee on cordwood

fueling/appliance operation technical recommendations document: The workgroup will 

draft a report that details findings of the review, a recommended path forward, and areas 

where a lack of consensus or data gaps prevented the development of recommendations. 

This report will be presented to the Steering Committee. A joint meeting of the 

workgroups and Steering Committee will be held to brief the EPA.
34

6.3 EPA’s Approval Process for Alternative Methods

While the cordwood test method review and analysis is underway, EPA’s Measurement 

Technology Group has responsibility for the approval of alternative test methods. 

For now, EPA’s Measurement Technology Group will make case-by-case approvals of 

alternative cordwood test methods. Regarding wood stoves, these case-by-case approvals will 

likely be based on the draft ASTM cordwood test method. During this time, the EPA will collect 

data from the approved alternative cordwood test methods to inform a more broadly applicable 

cordwood test method. Results of these tests will also be provided to the technical workgroups 

for their use in developing recommendations for the Steering Committee.

If sufficient data are collected via case-by-case reviews of alternative test methods, the EPA’s 

Measurement Technology Group may approve a broadly-applicable alternative cordwood test 

method. This broadly-applicable method could become the “default” alternative cordwood

method until an EPA reference method is promulgated. The EPA will collect data using this 

default cordwood method in order to inform an EPA reference method.
35

7.0 Topics for Further Consideration

The EPA has established a non-rulemaking docket for any comments submitted on this 

Discussion Paper under Docket ID No. EPA-HQ-OAR-2016-0130. All documents in the docket 

are listed in the www.regulations.gov index. If you want your input to be considered in the 

process, please send by June 30, 2016. Please submit your input, questions or suggestions 

relevant to this Discussion Paper to Docket ID No. EPA-HQ-OAR-2016-0130, by one of the 

following methods:

 www.regulations.gov: Follow the on-line instructions for submitting comments.

 Email: a-and-r-docket@epa.gov, Attention Docket ID No. EPA-HQ-OAR-2016-0130.

 Mail: U.S. Postal Service to EPA Docket Center, EPA West (Air Docket), Attention 

Docket ID Number EPA-HQ-OAR-2016-0130, U.S. Environmental Protection Agency, 

Mailcode: 28221T, 1200 Pennsylvania Ave., NW, Washington, DC 20004.

The EPA will post all submitted non-CBI information to this publicly available website. If you 

need to submit CBI material, please contact Amanda Aldridge, EPA, Office of Air Quality 

Planning and Standards (OAQPS) for instructions at telephone number (919) 541-5268, or 

aldridge.amanda@epa.gov.

We suggest you provide comment on the following topics and provide data if applicable:

1. Table 3 Preliminary List of Key Criteria to be Considered for Cordwood Test Method

- provide feedback regarding the listed criteria and questions/notes in the Description, 

Metric and Other Considerations column. In addition, list and describe any important 

criteria that are missing from this table.

2. The most important aspects of in-home device fueling and operation by responding to 

some or all of the following questions:

o What are the most common fueling and operating practices by catalytic wood

stove users that lead to high emissions? 

o What are the most common fueling and operating practices by non-catalytic wood

stove users that lead to high emissions?

o What are the most common fueling and operating practices by hydronic heater 

(wood boiler) users that lead to high emissions? 

o What are the most common fueling and operating practices by forced-air furnace 

(warm-air furnaces) that lead to high emissions?

3. The importance of the test method (fueling and operating protocol) capturing the 

variability in emissions based on fuel species, fuel density, and moisture content.

Specify which types of devices you are referring to, such as catalytic wood stoves, 

non-catalytic wood stoves, hydronic heaters, or forced-air furnaces.
36

4. The importance of the test method (fueling and operating protocol) capturing 

emissions at the lowest and highest possible burn rates used by consumers. Be sure to 

specify which device(s) you are referring to in your comment.

5. The importance of the test method (fueling and operating protocol) capturing 

emissions when the firebox is loaded to full capacity. Be sure to specify which 

device(s) you are referring to in your comment.

6. The importance of the test method (fueling and operating protocol) capturing start-up 

and refueling emissions. Be sure to specify which device(s) you are referring to in 

your comment.

7. Updates that should be made to the PM measurement method to improve the 

sampling and analytical protocol. 
37

8.0 Endnotes for All Sections

1 Consensus Positions of WESTAR, NESCAUM, and HPBA re “Proposed Standards of Performance for 

New Residential Wood Heaters, New Residential Hydronic Heaters and Forced Air Furnaces, and New 

Residential Masonry Heaters”. Available at http://www.regulations.gov/#!documentDetail;D=EPAHQ-OAR-2009-0734-1712. August 18, 2014.

2 U.S. EPA. Wood Stove Emissions, Particle Size and Chemical Composition, EPA-600/B-0050. Prepared

by National Risk Management for the Office of Air Quality Planning and Standards, Research Triangle 

Park, NC 27711. June 2000.

3 Seljeskog, Morten, et al. Particle emission factors from wood stove firing in Norway, Report by SINTEF 

Energy Research to the Norwegian Climate and Pollution Agency, 2013-04-11 V7, Report No. TR 

A7306, ISBN 978-82-594-3607-8. April 11, 2013. 

4 U.S. EPA. 2011 National Emissions Inventory (NEI) Data, Version 2. Available at 

http://www3.epa.gov/ttnchie1/net/2011inventory.html. (2011 NEI Data also available at 

https://www.epa.gov/air-emissions-inventories/2011-national-emissions-inventory-nei-data; 2011 

NEI Documentation available at https://www.epa.gov/air-emissions-inventories/2011-nationalemissions-inventory-nei-documentation.) Released March 4, 2015.

5 U.S. EPA. National Air Toxics Assessment, 2011 NATA: Assessment Results. Available at 

http://www.epa.gov/national-air-toxics-assessment/2011-nata-assessment-results#nationwide. The 

NATA Technical Support Document is available at http://www.epa.gov/sites/production/files/2015-

12/documents/2011-nata-tsd.pdf. Released December 17, 2015.

6 U.S. EPA. Strategies for Reducing Residential Wood Smoke. EPA–456/B–13–001. Prepared by the 

Outreach and Information Division, Office of Air Quality Planning and Standards, U.S. EPA, Research 

Triangle Park, NC 27711. pp. 4–5. Available at http://www.epa.gov/burnwise/burn-wise-strategiesreducing-residential-wood-smoke. March 2013.

7 U.S. EPA. Estimated Contribution of Fine Particle Emissions from Wood Combustion in Four U.S. 

Cities. Memorandum from David Cole, Office of Air Quality Planning and Standards, U.S. EPA to 

Docket ID No. EPA-HQ-OAR-2009-0734. Available at 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-0144. April 4, 2013.

8 Schrieber, Judith and Robert Chinery. Smoke Gets in Your Lungs: Outdoor Wood Boilers in New York 

State, prepared for the Office of the Attorney General of New York. Revised March 2008. Available at 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-0079. See also

Preliminary Results of a Study to Assess Air Quality Impacts Associated with Outdoor Wood Boiler Use, 

prepared by Judy Abbot of the Bureau of Toxic Substance Assessment for the NYS Department of 

Health, overview available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-

0734-0080. December 11, 2009.

 
38

 

9 Marin, Arthur, Executive Director of NESCAUM. Letter to Gina McCarthy of the U.S. EPA. Available 

at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-0070. January 14, 

2011.

10 See the Docket for the Residential Wood Heater New Source Performace Standards at 

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OAR-2009-0734. 

11 Marin, Arthur Marin, Executive Director of NESCAUM and Dan Johnson, Executive Director of 

WESTAR. Letter to Steve Page of U.S. EPA. Available at 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-0244. April 29, 2008.

12 Collier, David, President of WESTAR. Letter to Steve Page of the U.S. EPA. Available at 

http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-0071. July 18, 2011.

13 Department of Ecology, State of Washington. How Wood Smoke Harms Your Health. Pub. No. #09-02-

021. Available at http://www.ecy.wa.gov/pubs/91br023.pdf. Revised June 2012.

14 Liu LJ, et al. “Exposure assessment of particulate matter for susceptible populations in Seattle”. 

Environ Health Perspect 111(7): 909-918. 2003.

15 Barn P, Larson T, et al. “Infiltration of forest fire and residential wood smoke: an evaluation of air 

cleaner effectiveness”. Journal of Exposure Science and Environmental Epidemiology 18: 503–511. 2008.

16 Brown, David, et al. “Outdoor Wood Furnaces Create Significant Indoor Particulate Pollution In 

Neighboring Homes”. Inhalation Toxicology 26.10: 628–635. DOI: 10.3109/08958378.2014.946633. 

2014.

17 U.S. EPA. National Air Toxics Assessment, 2011 NATA: Assessment Results. Available at 

http://www.epa.gov/national-air-toxics-assessment/2011-nata-assessment-results#nationwide. The 

NATA Technical Support Document is available at http://www.epa.gov/sites/production/files/2015-

12/documents/2011-nata-tsd.pdf. Released December 17, 2015.

18 Department of Ecology, State of Washington. How Wood Smoke Harms Your Health. Pub. No. #09-02-

021. Available at http://www.ecy.wa.gov/pubs/91br023.pdf. Revised June 2012.

19 Liuhua Shi, et al. “Low-Concentration PM2.5 and Mortality: Estimating Acute and Chronic Effects in a 

Population-Based Study”. Environ. Health Perspectives, 124:46-52. 

http://dx.doi.org/10.1289/ehp.1409111. January 2016.

20 Department of Ecology, State of Washington. How Wood Smoke Harms Your Health. Pub. No. #09-02-

021. Available at http://www.ecy.wa.gov/pubs/91br023.pdf. Revised June 2012.

21 U.S. EPA. “Wood Smoke and Your Health”. EPA’s Burn Wise website, available at 

http://www.epa.gov/burnwise/wood-smoke-and-your-health. See also EPA’s website regarding the 

Health Effects of PM at http://www3.epa.gov/airquality/particlepollution/health.html. February 2016.

22 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.
39

 

23 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

24 Canadian Standards Association, B415.1-10 Performance Testing of Sold-Fuel-Burning Heating 

Appliances, (CSA, 5060 Spectrum Way, Suite 100, Mississauga, Ontario, Canada, 2010), Annex C, p. 71. 

March 2010.

25 Houck, James E. Review of the Puget Sound Clean Air Agency December 5, 2012 letter to Mr. Stephan 

D. Page of the Office of Air Quality Planning and Standards U.S. Environmental Protection Agency, page 

1. April 3, 2013. Attachment 10 of HPBA’s comments on the Proposed NSPS for Residential Wood 

Heaters, available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1643. 

26 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

27 Consensus Positions of WESTAR, NESCAUM, and HPBA re “Proposed Standards of Performance for 

New Residential Wood Heaters, New Residential Hydronic Heaters and Forced Air Furnaces, and New 

Residential Masonry Heaters”. Available at http://www.regulations.gov/#!documentDetail;D=EPAHQ-OAR-2009-0734-1712. August 18, 2014.

28 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 13. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

29 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 19. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

30 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

31 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 13. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

32 Allen, G. Contribution of Wood Smoke to Particle Matter Levels in Connecticut - Source 

Characterization of Outdoor Wood Furnaces. NESCAUM, p. 4-1. Available at 

http://www.vtwoodsmoke.org/pdf/CT-NESCAUM_OWB_Test_Rpt.pdf. September 9, 2008.

33 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 19. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.
40

 

34 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

35 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

36 Burnet, Paul G., Edmisten, Norman G., Tiegs, Paul E., Houck, James E. and Rachel A. Yoder.

Particulate, Carbon Monoxide, and Acid Emission Factors for Residential Wood Burning Stoves, Journal 

of the Air Pollution Control Association, 36:9, 1012-1018, DOI: 10.1080/00022470.1986.10466139. 

1986.

37 Preto, F. Emissions from Residential Wood Combustion. Presentation at IEA Task 32 Workshop, Paris, 

France. Available at: http://www.ieabcc.nl/workshops/task32_Paris_ssc/Preto.pdf. October 21, 2005.

38 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

39 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 19. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

40 Leese, K.E. and Harkins, S.M. Effects of Burn Rate, Wood Species, Moisture Content and Weight of 

Wood Loaded on Woodstove Emissions, Prepared for the U.S. Environmental Protection Agency by 

Research Triangle Institute, Research Triangle Park, NC, EPA-600/2-89-025. 1989.

41 Houck, James E. Review of the Puget Sound Clean Air Agency December 5, 2012 letter to Mr. Stephan 

D. Page of the Office of Air Quality Planning and Standards U.S. Environmental Protection Agency. 

April 3, 2013, Attachment 10 of HPBA’s comments on the Proposed NSPS for Residential Wood 

Heaters, available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1643. 

42 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 17. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

43 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 14. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.

44 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-1551. May 

5, 2014.

45 Rector, Lisa of NESCAUM. Conversation with U.S. EPA. February 2016.
41

 

46 New York State Energy Research and Development Authority (NYSERDA), Environmental, Energy 

Market, and Health Characterization of Wood-Fired Hydronic Heater Technologies, Executive Summary, 

Prepared for NYSERDA by the USEPA, ARCADIS, Post-Doctoral Fellows to the USEPA and the 

University of Dayton Research Institute, NYSERDA Report 12-15. Pages.S-5, S-6. 

https://www.nyserda.ny.gov/-/media/Files/Publications/Research/Environmental/Wood-FiredHydronic-Heater-Tech-Summary.pdf. June 2012.

47 Rector, Lisa of NESCAUM. Conversation with U.S. EPA. February 2016.

48 New York State Energy Research and Development Authority (NYSERDA), Environmental, Energy 

Market, and Health Characterization of Wood-Fired Hydronic Heater Technologies, Executive Summary, 

Prepared for NYSERDA by the USEPA, ARCADIS, Post-Doctoral Fellows to the USEPA and the 

University of Dayton Research Institute, NYSERDA Report 12-15, page S-9. 

https://www.nyserda.ny.gov/-/media/Files/Publications/Research/Environmental/Wood-FiredHydronic-Heater-Tech-Summary.pdf. June 2012.

49 Gras, J., Meyer C., Weeks, I., Gillett, R., Galbally, I., Todd, J., Carnovale, F., Joynt, R., Hinwood, A., 

Berko, H. and S. Brown. Emissions from domestic solid fuel burning appliances (wood-heaters, open 

fireplaces). Environment Australia, March 2002.

50 Burnet, Paul G., Edmisten, Norman G., Tiegs, Paul E., Houck, James E. and Rachel A. Yoder.

Particulate, Carbon Monoxide, and Acid Emission Factors for Residential Wood Burning Stoves, Journal 

of the Air Pollution Control Association, 36:9, 1012-1018, DOI: 10.1080/00022470.1986.10466139. 

1986.

51 OMNI Environmental Services, Effects of Design Factors on Emissions from Non-Catalytic Residential 

Wood Combustion Appliances, p.15, Prepared for the U.S. EPA. May 1986.

52 Leese, K.E. and Harkins, S.M. Effects of Burn Rate, Wood Species, Moisture Content and Weight of 

Wood Loaded on Woodstove Emissions, Prepared for the U.S. Environmental Protection Agency by 

Research Triangle Institute, Research Triangle Park, NC. EPA-600/2-89-025. 1989.

53 Houck, James E., Pitzman, Lyrik Y., and Tiegs, Paul. Emission Factors for New Certified Residential 

Wood Heaters. Presented at the 17th Annual Internation Emission Inventory Conference 

(http://www3.epa.gov/ttnchie1/conference/ei17/) by OMNI Environmental Services and Test 

Laboratories. http://www3.epa.gov/ttn/chief/conference/ei17/session4/houck.pdf. June 2-5, 2008.

54 Allen, George, et al of NESCAUM.Contribution of Wood Smoke to Particle Matter Levels in 

Connecticut – Source Characterization of Outdoor Wood Furnaces. 

http://www.nescaum.org/documents/source-characterization-of-outdoor-wood-furnaces/. 

September 9, 2008.

55 NESCAUM’s comments to the U.S. EPA regarding the Proposed NSPS for Residential Wood Heaters, 

page 13. Available at http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2009-0734-

1551. May 5, 2014.
42

9.0 Appendix

 Table A-1: Summary Table of Wood Stove Cordwood Test Methods

 Table A-2: Summary Table of Hydronic Heater Cordwood Test Methods

 Table A-3: Summary Table of Forced-Air Furnace Cordwood Test Method
43

Table A-1. Summary Table of Wood Stove Cordwood Test Methods 

Parameter

Draft ASTM “Standard Test Method for 

Determining PM Emission from Wood heaters 

using Cordwood Test Fuel” 

AS/NZS 4012 & 4013:2014 “Domestic solid 

fuel burning appliances” methods for 

determination of power output & efficiency 

and determination of flue gas emission

EN 13240 “Roomheaters fired by solid fuel. 

Requirements and test methods”

Full load Partial load

Feed Manual - Cordwood Manual (batch) - Cordwood Manual - Cordwood

Test Type Cold to Hot (high burn)

Hot to Hot (medium and low burns) Hot to Hot Hot to Hot

Measurement Method Dilution tunnel Dilution tunnel Direct flue gas

Fuel requirements Cordwood

Multiple species allowed within a set specific 

gravity range (0.48-0.73), free of decay, fungus 

& loose bark

Cordwood

Hardwood and softwoods with specified 

density range, moisture content and ash 

content

Cordwood

Multiple species including birch and beech

Fuel moisture (dry, unless 

specified) 19-25% (load average) 16-20% (softwood, wet basis)12-16% (hardwood, wet basis) 13.4-20%

Method of Efficiency

Determination Stack Loss (Indirect) Method Direct Method (calorimeter room used to measure energy output vs input) Stack Loss (Indirect) Method

Number of categories 3 3 (with 3 runs/”cycles” per burn rate) 2

Burn Rates 100%

Lowest setting ≤ 1.15 kg/h

Between lowest and highest air settings

High (controls fully open)

Low (controls open minimally)

Medium (following high & low rates)

100% 30%

Test Duration Returns to weight prior to loading or 90% 

consumed and no weight loss for at least 30 

minutes (for high burn)

Mass of test fuel load is consumed to within 

±0.5% of mass of test fuel load

Entire fuel charge has 

been burnt & only 

ash remains

Returns to weight 

prior to loading the 

fuel charge

Pollutants Total PM

CO Total PM

Filterable PM,

CO, Nitrogen Oxide,

VOCs

Metric Grams per hour Grams per kilogram (dry fuel burned) Gram per megajoule

Emission rate calculation Weighted average = 40% low burn average + 

40% medium burn average + 20% high burn 

average

Arithmetric mean of the average PM emissions 

at each burn rate Reported by load, no averaging

Startup emissions Captured in high burn run, cold to hot No No

Steady state emissions Low and medium burn rates Yes Yes

Shutdown emissions No No No

CO measurement CSA B415.1, Clauses 6.2.2, 10.4.3 No Yes
44

Table A-2. Summary Table of Hydronic Heater Cordwood Test Methods

Parameter ASTM E2618-13 BNL Partial Storage Method EN 303-5 CSA B415.1

Manual Loaded Fuel Cordwood Cordwood Cordwood Both cordwood and crib wood

Feed: 

Manual/Automatic/Both Both Manual Both - wide range including coal

Both - wide range but not 

including coal

Wood Fuel Species Any within specified density 

range

white or red oak 5 species optional Any within specified density 

range

Moisture range (dry basis) 19-25% 19-25% 13.4-20% 18-28%

Method of Efficiency 

Determination Thermal Output Thermal Output Thermal Output Stack Loss Method

Number of Categories 4

5 4 with 2 as optional 2 4

Lowest Output Tested -

Manual Feed 15% 15% 50%4 35%

PM Emission Metric Annual average lb/MMBtu 

output

Annual average lb/MMBtu 

output

Average over two periods at 

full load - mg/m3

Simple average of test runs -

lb/MMBtu output

PM Emission Rate (g/hr) YES - RUN AVERAGE YES - by phase of burn cycle NO3 NO

Startup NO YES NO NO

Steady State NO YES NO NO

End NO YES NO NO

Dilution Tunnel or In-Stack Dilution Tunnel Dilution Tunnel In-Stack Dilution Tunnel

Thermal Storage? No, partial, or full PARTIAL NO NO

Cold Start? YES- with storage6 YES- Cat I and II NO NO

CO Required to be measured? YES YES YES YES

CO emission metric? NO YES YES YES

CO emission limit NO NO YES NO

Emissions measured for 

phases of burn cycle? NO YES Measurement during 2 segments only NO

Upper size limit NO 350,000 Btu/hr2 500 kW (1.7 MMBtu/hr) 500,000 Btu/hr

Fuel Loading 10 lb/ft3 10 lb/ft3 Manu Specifications 10 lb/ft3

Notes

1. By reference to the EPA Partnership Agreement

2. By reference to EPA M28 WHH

3. Not reported but could be estimated from measured data

4. PM only tested during full load (nominal) output test

5. Tests are run in four categories with no storage or partial storage. With full storage there is only one run condition but this is repeated 3 times.

6. With partial thermal storage the Category I (15%) and II (25%) runs are done with cold start. The Category III and IV runs are done with a hot start. With full storage, 

only a cold start is used. 
45

Table A-3. Summary Table of Forced-Air Furnace Cordwood Test Method

Parameter CSA B415.1

Manual Loaded Fuel: Crib, Cord, or Both Addressed Both - wide range but not including coal

Feed: Manual/Automatic/Both Both - wide range but not including coal

Wood Fuel Species Any within specified density range

Moisture range (dry basis) 18-28%

Method of Efficiency Determination Stack Loss Method

Number of Categories 4

Lowest Output Tested - Manual Feed 35%

PM Emission Metric Simple average of test runs - lb/MMBtu output

PM Emission Rate (g/hr) NO

 Startup NO

 Steady State NO

 End NO

Dilution Tunnel or In-Stack Dilution Tunnel

Thermal Storage? NO

Cold Start? NO

CO Required to be measured? YES

CO emission metric? YES

CO Emission Rate (g/hr) NO

CO emission limit NO

Emissions measured for phases of burn cycle? NO

CO Emission Rate vs Time Required NO

Upper size limit 500,000 Btu/hr

Fuel Loading for hand-fed units (minimum) 10 lb/ft3