Air Emissions from Residential Heating: The Wood Heating Option Put into
Environmental Perspective
James E. Houck and Paul E. Tiegs
OMNI Environmental Services, Inc., Beaverton, OR
Robert C. McCrillis
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
U.S. Environmental Protection Agency
Research Triangle Park, NC
Carter Keithley and John Crouch
Hearth Products Association
Arlington, VA
Approximately 6 x 1015 Btu (6.3 x 1018 joules) of energy was consumed for space heating
in 1997 in the United States, representing about $45 billion in expenditures. There were an
estimated 99 million households in the U.S. in 1997, most of which required some form of space
heating. The major space heating energy options are natural gas, fuel oil, kerosene, liquefied
petroleum gas (LPG), electricity, coal and wood. Each of these residential space heating options
has air quality issues associated with it. To accurately compare national or global scale air quality
impacts among energy options, emissions from off-site production, processing, and
transportation of the energy need to be taken into consideration along with the pollutants emitted
locally from individual residences.
Residential wood combustion (RWC) meets 9% of the Nation's space heating energy
needs and utilizes a renewable resource. Wood is burned regularly in about 30 million homes.
Residential wood combustion is often perceived as environmentally dirty due to elevated
emissions of fine particles from older wood burning devices. In response to this emission
problem, lower emitting new technology wood heating devices have been developed by industry,
and the U.S. Environmental Protection Agency requires new stoves to be certified by undergoing
emission testing. Only about 11% of the RWC appliance types subject to certification and in use
today are either certified or can be considered new technology devices. Other RWC devices, such
as fireplaces and furnaces, are not subject to national certification requirements, and many that
are currently in use are older appliances due to their long usable lifetime. Therefore, most of the
existing air quality impacts and the perception of the potential impacts from wood heating are
still based on old technology devices.
This paper compares the national scale (rather than local) air quality impacts of the
various residential space heating options. Specifically, the relative contributions of the space
heating options to fine particulate emissions, greenhouse gas emissions, and acid precipitation
impacts are compared.

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INTRODUCTION
In 1993 all but 0.9 %(mostly located in Hawaii) of the 99 million households in the
United States had some form of space heating1,2. Significantly, energy for space heating
represents about 8% of the total energy consumed for all purposes, including transportation, in
the United States2*3. Considerable ancillary energy beyond the 8% is also needed for the ultimate
production of space heat. Notably, this includes energy for such activities as extracting,
transporting, processing, and distributing fossil fuels. All forms of energy consumption have
associated environmental and human health impacts. These include impacts to the ambient air,
water, and land media. Terms such as "total environmental costs" (TECs), "environmental
externalities," and "energy return on investment" (EROI) have been introduced to facilitate the
assessment of the real environmental and societal costs of energy4"7.
The major energy sources for residential space heating, in descending order of end-use
energy consumption, are natural gas, fuel oil, wood, electricity, liquefied petroleum gas (LPG),
coal, and kerosene (Table 1). Due to electric power-plant inefficiencies and transmission line
losses, about three times the amount of energy consumed by the residential end user for electrical
space heat is needed for its production. Further, in regards to electricity's use for space heating, it
should be noted that electricity is not a primary source of power and it is, in turn, produced
principally by fossil fuel combustion. Table 2 shows the total energy by primary source
consumed for residential space heating calculated by adding energy consumed for space heating
directly at residences with the energy by source type consumed to produce electricity
subsequently used for space heating. Not including the ancillary energy requirements for
activities such as extracting, transporting, processing, and distributing fuels, about 86% of the
energy consumed for residential space heating is from fossil fuels. About 8% is from wood. The
remaining 6% is principally from nuclear and hydroelectric sources used to produce electricity.
Among the various categories of environmental and human health impacts, the research
reported here was focused on national scale (global) air quality issues. The three topical and
national scale air quality issues most relevant to residential space heating are: 1. fine particulate
emissions, for their impact on visibility and human health, 2. greenhouse gases; and 3. acid
precipitation. (The ozone impact is not relevant to space heating sources even though they
produce significant volatile organic compound (VOC) and nitrogen oxide ozone precursors since
elevated ozone is primarily a summertime phenomenon.) Total impacts for each of the three
national scale air quality categories for each space heating option were calculated by summing
the contributions of emissions from off-site activities performed to obtain the subsequent space
heating energy with emissions directly from space heating sources in residences. The base year
1993 was used for the comparisons because it was the most recent year for which the extensive
data needed for the comparisons were readily available. In conducting the evaluations, special
emphasis was placed on putting emissions from RWC into perspective with other options.
THE STATUS OF RESIDENTIAL WOOD COMBUSTION
There are approximately 37 million RWC appliances in the United States (Table 3).
These include 9.3 million wood stoves, 27 million fireplaces, and about 0.6 million other
appliance types2,8'9. (Other appliance types include pellet stoves, masonry heaters, and wood-fired
furnaces.) About 7 million of the 27 million fireplaces are seldom used9,10. Most of the fireplaces
2

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that are used are used either as supplemental heating sources or for minor heating or aesthetic
purposes10. Only 0.4 million are used as primary heating sources; most of these are located in the
Southeast2. Surveys have shown that, of 7.1 million fireplaces with inserts, 0.3 million are
Environmental Protection Agency (EPA) certified911. Of the 9.3 million wood stoves, about 1
million are EPA certified9,11.
EPA promulgated New Source Performance Standards (NSPS) for wood heaters which
establish threshold particulate emission rates for wood heaters to be certified12. Since 1992, only
certified affected facilities3 can be sold in the United States. Wood stoves, cordwood fireplace
inserts, pellet stoves, and pellet inserts covered by the regulation must pass through the EPA
certification process. Fireplaces themselves are exempt from EPA certification; however, the
state of Washington does have certification requirements for them13.
It has been estimated that 28% of the cords of wood burned annually are burned in
fireplaces and 12% are burned in wood stoves14. Because only about 11% of the wood stoves
currently in use are EPA certified, only 4% of the fireplace inserts are EPA certified and only one
state now requires new fireplaces to be certified, the majority of wood is currently burned in
older technology appliances. Importantly, the perception of RWC as being an especially
environmentally "dirty" heat source is based largely on the relatively high fine particulate
emissions of the older technology units. Considerable improvements have been made in the
environmental performance of RWC appliances in the last decade15,16. It must be noted, however,
that achieving low emissions throughout the life of these new technology appliances requires that
they be maintained and operated properly. Several studies17"23 have shown that, if either of these
requirements is not satisfied, emission control performance can degrade significantly.
EMISSION FACTORS AND ACTIVITY LEVELS
National emissions of acid equivalents, fine particles, and the mass of carbon equivalents
of greenhouse gases were obtained from emission factor and activity level compilations2,3*24*30.
Each of these three measures of pollutant emissions was normalized by the number of quads of
energy delivered nationally for residential space heating by energy source. The final units for
comparisons of acid precipitation, fine particulate, and greenhouse gas impacts were billion acid
equivalents per quad, thousand short tons of particles per quad, and million short tons of carbon
equivalents of greenhouse gases per quad, respectively.
The overall in-home effectiveness of heating appliances was not taken into consideration
in normalizing the air pollutant emissions per unit of energy for the various categories because its
effect will be small as compared to many of the other factors evaluated. The overall effectiveness
of appliance types is influenced by the inherent efficiency of the appliance type, by usage
characteristics and by siting practices. Siting refers to the location of the appliance in the home;
e.g., next to an exterior wall versus the center of the home. Usage characteristics refer to such
factors as the unused energy waste associated with the convenience of furnace type appliances
heating an entire home, even when all or part of it is not occupied. When all these factors are
a Some wood stoves and pellet stoves are exempt from regulation. For example, if
the device has an air to fuel ratio > 35:1, it is exempt. Or if the minimum burnrate
is > 5 kg/hr, it is exempt.
3

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considered, industry experts agree that the overall effectiveness differences in home heating
options are small.
The sequence of linked activities which connect the supply of a specific energy resource
with a specific end use has been referred to as the energy trajectory. For example, for coal, the
energy trajectory to the residential space heating end use consists of: 1. extraction (surface or
underground mining), 2. transportation from the mine to the processing plant (trucking,
conveyor, or mine rail), processing (cleaning, sulfur removal, crushing, sizing, and drying),
storage (above- and underground piles, silos, or bins), and distribution (unit train, mixed train,
river barge, pipeline slurry, trucking, and/or conveyors) to a coal-fired power plant or to a
residential heating unit. If the coal is delivered to a coal-fired power plant for power generation,
two additional components of the energy trajectory are the actual power generation process and
the transmission of the power produced to the electric home heater. Not only do emission factors
and activity levels for each pollutant need to be determined for each step and finally summed to
obtain an overall emission value, but the efficiency of each step must also be estimated since
most emission factors are based on a mass of pollutant emitted per unit of energy or quantity of
fuel at that step in the trajectory. Successive efficiency losses with each step of the trajectory
have the effect of causing more energy or energy equivalents to pass through the initial stages of
the trajectory with a commensurate increase in the total air emissions.
Natural gas and petroleum have similar trajectories as coal (i.e., extraction, transportation
to processing facilities, processing, and transportation to a power plant or residential heating
unit). The petroleum trajectory is complex since production and processing of LPG, kerosene,
distillate oil, and residual oil are interrelated.
The energy trajectory for wood to residential home heating is quite different and simpler
than for fossil fuels. Emissions from the actual home heating combustion step dominate the
overall emission values for its energy trajectory. The energy return on investment (EROI) for a
commercial wood chipping operation was determined to be 27.6 to 1 (i.e., 1 unit of fossil fuel
was required to produce 27.6 units of energy from wood)6. The largest fraction of this was the
fossil fuel needed for a 240 km round trip for fuel pickup. The same study concluded that the
typical EROI for cordwood harvesting and transport would be even higher.
GREENHOUSE GASES
Carbon dioxide (C02), methane (CH4), and nitrous oxide (N20) are the principal
greenhouse gases from energy sources. The capacity of CH4 and NzO to trap heat and their
lifetime in the atmosphere produce a relative global warming potential (GWP) of 21 and 310,
respectively, as compared to C02 which has a relative GWP of I27. The standard convention for
reporting total greenhouse gas effects is to multiply the emissions of CH4 and N20 by 21 and
310, respectively, then add these values to the CO? value. The effective C02 value produced by
summing the contributions of the various greenhouse gases adjusted to C02 by the GWP is then
converted to a carbon equivalent. This simply means that the value is multiplied by the ratio of
12/44 which converts the mass of greenhouse gas to the mass of carbon that would be in the
greenhouse gases if they were all C02.
In reviewing the relative contributions of C02, CIi4, and N20 to the greenhouse effect, it
was discovered that C02 from combustion dominates the impact for all energy sources used for
4

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home heating. Among the energy sources, the relative greenhouse contribution of CH4 is the
highest for natural gas for which it represents 11% of its total greenhouse effect. This is
reasonable considering that natural gas is composed primarily of CH4 and that considerable
natural gas losses occur in the extraction, transport, and processing of natural gas. For both
electricity and direct coal heating, CH4 accounts for about 4% of the greenhouse impact. The
contribution of CH4 to the greenhouse impact is less than 1% for all other home heating energy
sources. The contribution of N20 to the greenhouse impact is less than 1 % for all energy sources
used for home heating. The emissions of carbon monoxide (CO), nitrogen oxides (NOx), and
nonmethane volatile organic compounds (NMVOCs) were reviewed since they can indirectly
impact concentrations of greenhouse gases. It was concluded, based on their emission factors and
their atmospheric fate, that their contributions would be small.
The total carbon C02 emissions from RWC were reduced by 40% in the final tabulations
because the harvesting of more mature trees for cordwood permits rapid carbon fixation in
younger replacement trees. While carefully managed wood fuel plantations could achieve a
nearly "greenhouse gas neutral" condition, a reasonable estimate of the steady state condition
produced by standard wood harvesting practices is that 40% of the carbon emitted by RWC is in
the form of fixed carbon6,31.
The results of the greenhouse gas analysis are illustrated in Figure 1. Residential wood
combustion has the lowest effective greenhouse impact per unit of energy delivered followed by
natural gas. Electricity has the highest greenhouse impact, with the direct use of coal and
petroleum being intermediate in impacts. It is reasonable that electricity has a higher impact than
either coal or petroleum burned directly in home heating appliances since 1.22 quads of energy
was consumed by electric power generating units in 1993 to produce only 0.41 quads delivered to
residences for home heating and since coal and petroleum together account for 64% of the
electrical energy generated.
FINE PARTICLES
Atmospheric fine particles originate from two processes; i.e., from the direct emissions of
particles (primary particles) and from the transformation of emitted gases once they are in the
atmosphere (secondary particles). The principal sources of secondary particles are the formation
of ammonium sulfate from sulfur dioxide (S02) gas and the formation of ammonium nitrate from
NOx gases. Consequently, the emissions of primary particles as well as S02 and NOx were
evaluated to estimate the effective fine particulate impacts of the various home heating options.
S02 gas is produced by combustion and is directly related to the sulfur content of the fuel.
S02 is also released in the energy trajectory of fossil fuels during desulfurization steps. NOx
gases are produced by combustion, both from nitrogen contained in the fuels and from the
oxidation of atmospheric nitrogen at high temperatures. It is estimated that about 30% of S02 gas
is converted to secondary particles32. The fraction of NOx gases converted to ammonium nitrate
can be estimated by comparing national emission inventories and typical national particulate
nitrate concentrations26*33. The value for the conversion of NOx gases to ammonium nitrate
particles is about 7.4%.
Besides secondary particles produced from S02and NOx gases, secondary particles can
also be formed from NMVOCs; however, the effect appears to be small relative to secondary
5

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particles formed from S02 and NOx gases34. Further, for sources such as RWC, that have
particles composed of a high percentage of organic compounds, there appears to be' a net loss of
organic material from particles due to volatilization"15.
PMI0 emission inventories were used to estimate primary fine particulate (PM2 5)
emissions since the majority of PM,0 particles formed from combustion are also PM25 particles.
(The fugitive PM2t5 emissions from coal mining were estimated to make up 10% of the PM,0
emissions.) Secondary particles are overwhelmingly PM25 particles, and secondary particulate
contributions were added directly to the primary particulate values to obtain an effective fine
particulate impact per unit of heat delivered for residential heating. Before addition, S02 and
NOx emissions (as nitrogen dioxide) were multiplied by 0.30 and 0.074, respectively, to obtain an
estimate of the amount of secondary particles that they would produce.
For all sources except RWC, secondary particles make up the majority of the total
effective fine particulate values. Except for natural gas, secondary ammonium sulfate alone
makes up between 65% and 90% of the values of these sources. In the case of natural gas,
secondary ammonium nitrate accounts for 72% of the effective fine particulate value, and
secondary ammonium sulfate accounts for 22%. Primary particles formed by combustion make
up 98% of the effective particulate value for RWC.
The results of the fine particulate analysis are illustrated in Figure 2. As can be seen,
natural gas has the lowest effective fine particulate emissions per unit of heat delivered for
residential heating, followed by LPG. Residential wood combustion has the highest value. The
direct use of coal and electricity also show high values with fuel oil and kerosene intermediate in
values. It should be noted that the emission factors for RWC used in this analysis primarily
reflected old technology wood heaters and that a 50% reduction in the value shown in Figure 2 is
reasonably achievable with new technology devices1516. It should also be noted that a reduction in
particulate emissions by 50% or more makes RWC comparable to electricity in terms of effective
fine particulate emissions. The projected fine particulate emissions from using new technology
wood burning appliances are shown in Figure 2 above the caption "new wood." This projection
includes the weighted effect of replacing both old technology wood stoves and using advanced
fireplaces designs and/or using manufactured fuels in fireplaces. It also assumes that stoves are
maintained to the extent required to eliminate any emissions control degradation. Furthermore, it
assumes that they are operated properly. As with wood stoves, new technology coal stoves
should reduce particulate emissions below that shown in Figure 2 since many coal appliances in
use are older units. However, there are no data to estimate the magnitude of this expected
reduction in emissions for coal-fired heaters. Also, in regards to residential coal use, higher
quality fuel (e.g., anthracite) will reduce particulate and acid gas emissions if utilized more
widely in home heating units.
ACID PRECIPITATION
Emissions of NOx and S02 gases forming nitric acid (HN03) and sulfuric acid (H2S04),
respectively, are the primary causes of acid precipitation. Both HN03and H2S04are strong
mineral acids with H2S04 producing two equivalents of acid per mole (two H+ ions per
molecule). Weak organic acids (carboxylic acids) are also emitted into the atmosphere,
particularly from combustion sources such as RWC36, but their impact on acid precipitation is
6

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very small34. Interestingly, organic acids in the presence of strong mineral acids tend to raise the
pH (lessen the acidity) due to their buffering capacity.
Acid equivalents emitted per unit of energy delivered for residential heating were
calculated to compare acid impacts among the energy sources. While emissions of both NOx and
S02 contribute to acid impacts, it is interesting to note that the contribution from NOx was about
an order of magnitude higher than S02 for natural gas, and the reverse was true for coal directly
burned in coal heaters. For all other energy sources, the contributions of NOK and S02 to acid
impacts were within a factor of 10 of each other. Similarly, while all steps in the energy
trajectory contributed to acidic impacts, the combustion step (as compared to extraction,
processing, and transportation steps) dominated the impact for the electricity, wood, and coal
sources. For petroleum and natural gas sources, the combustion step contributions were within
the same order of magnitude as the combined preparatory steps.
The results of the acid impact analysis are illustrated in Figure 3. Wood combustion has
the lowest acid impact per unit of energy, followed by natural gas and LPG. Coal has the highest
value and electricity the second highest (Coal combustion accounts for about 56% of the energy
consumed in electric power generation.) The acidic impacts per unit of heat delivered from fuel
oil and kerosene are intermediate, with kerosene being lower than fuel oil primarily because there
is less sulfur in kerosene than in No. 2 distillate fuel oil.
CONCLUSIONS
•	When the contributions of all the components of energy production for residential space
heating and the atmospheric fate of pollutants are taken into consideration, wood
combustion has the lowest greenhouse gas and acid precipitation impacts per unit of heat
delivered among the energy options. Its fine particulate impact based on existing wood
burning appliances was the highest among the options.
•	The direct in-home use of natural gas has the lowest fine particulate impact per unit of
heat.delivered. While not as low as RWC, natural gas also has low greenhouse gas and
acid precipitation impacts.
•	Average reductions in fine particulate values greater than 50% can be achieved with new
wood burning appliances, but this level of performance over the appliance's lifetime
requires careful attention to routine maintenance and proper operation of the appliance.
•	In regards to national or global scale air quality impacts, residential wood heating with
new technology appliances, assuming the degradation issue is properly addressed, and the
direct use of natural gas are sound environmental options.
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U.S. Environmental Protection Agency, October 1997.
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Old-Growth Forests to Young Forests," Science, 1990, v. 247, p. 699-702.
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the Haze in the United Sates: An Analysis of Data from the IMPROVE Network; Cooperative
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35.	Rau, J.A.; "Do Residential Wood Smoke Particles Lose Organic Carbon During Their
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Air Pollution Control Association, 1986, v. 36, pp 1012-1018.
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Table 1. Energy consumed by source for residential space heating in the United States3.

electricity
natural
gas
fuel oil
kerosene
liquefied
petroleum gas
(LPG)
wood
coal
households
(x 106)b
37.1
52.6
10.7
3.6
5.6
20.4
0.2
total energy
consumed
119
billion
kWh
3570
billion
cubic feet
6.51
billion
gallons
0.34
billion
gallons
3.25
billion
gallons
27.4
million
cords
3 million
short
tons
total energy
consumed
in quadsc
0.41
(1.22)d
3.67
0.90
0.05
0.30
0.55
0.06
percent of
total
6.9
61.8
15.1
0.8
5.1
9.2
1.0
a.	Information shown in the table was calculated from data in references 2 and 3.
b.	Many households have more than one source of heat; therefore, the sum of households by heat
source exceeds the total number of U.S. households (96.6 million in 1993).
c.	One quad is 1 quadrillion Btu (1015 Btu or 1.06 x 1018 joules).
d.	The 1.22 quad value in parentheses is the energy consumed by power plants to produce the
0.41 quad of electricity consumed in residences for space heating.
Table 2. Energy consumed by primary source for residential space heating in the United States3.

coal
natural gas
petroleumb
wood
nuclear
otherc
total energy consumed in quads
0.62
3.78
1.29
0.55
0.26
0.13
percent of total
9.5
57.0
19.4
8.3
3.9
2.0
a.	The energy consumed by primary source was calculated by summing the energy in fuel burned
directly in the households with the energy used by category (e.g., coal, petroleum, nuclear) to
produce the 1.22 quads of energy needed to produce 0.41 quad of electricity used for
residential space heating. Information shown in the table was calculated from data in
references 2 and 3.
b.	The petroleum category includes heavy and light oils (also referred to as residual and distillate
oils), kerosene, LPG, and petroleum coke.
c.	Hydroelectricity makes up the majority of the "other" category.
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Table 3. Residential wood combustion appliances in the United States.
appliance type
approximate number in use (millions)
wood stoves
9.3
EPA certified non-catalytic stoves
0.6
EPA certified catalytic stoves
0.4
non-certified older stoves
8.3
fireplaces11
27
masonry (site built)
5
factory builth
22
other appliance types
<0.6
pellet stovesc
0.3
masonry heaters
negligible
wood-fired furnaces
<0.3
a. Owners of about 7.0 million fireplaces reported not burning wood in them in the previous 12
month period. Of the 27 million fireplaces, approximately 7.1 million have inserts of which
0.5 million are EPA certified inserts.
b.	Factory built fireplaces are also commonly referred to as "zero-clearance" fireplaces.
c.	The pellet stove category includes both EPA certified units and those that are exempt from
certification requirements.
natural gas
electricity	fiiel oil	LPG	coal
Figure 1. Carbon equivalents of greenhouse gases per quad of heat delivered2*3,27.
11

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1000
electricity	ftiel oil	LPG	new wood
Figure 2. Effective fine particle emissions per quad of heat delivered. New wood value
assumes no emission control performance degradation of new technology stoves.
I	natural gas	I	kerosene	I	wood
electricity	fuel oil	LPG	coal
Figure 3. Acid equivalents emitted per quad of heat delivered.

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MT3l\;TPT pq-p n 007 TECHNICAL REPORTOATA
IN rUvlrU-^ ixiir xr oo 1 (Please read fmovctions on the reverse before completing)
1. REPORT NO. 2.
600/A-99/008
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Air Emissions from Residential Heating: The Wood
Heating Option Put Into Environmental Perspective
5. REPORT OATE
6. PERFORMING ORGANIZATION CODE
7.AUTH0RIS) J-Houck and p.Tiegs (OMNI), R. McCrillis
(EPA), and C.Keithley and J. Crouch (Hearth Prods.)
8. pcDcnouiM/: *"**~0ORT NO.
9. PERFORMING ORGANIZATION NAME AND ADORESS
OMNI Environmental Hearth Products Assn.
Services, Inc. 16U1 N« Kent street
5465 SW Western, Suite G Arlington, VA 22209
Beaverton, OR 97005
10	......		 .w.
11. CONTRACT/GRANT NO. p Q
7CR285NASX (CMNI)
12. SPONSORING AGENCY NAME ANO ADORESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT ANO PERIOD COVERED
Published paper; 6/97-7/98
14. SPONSORING AGENCY CODE
EPA/600/13
is.supplementary notes&PPQD project officer is Robert C. McCrillis, Mail Drop 61, 919/
541^2733. Presented at AWMA/EPA Conference, Emissions Inventory: Living in a
Global Environment, New Orleans, LA, 12/8-10/98.
16. abstract paper cornpares f.^e national scale (rather than local) air quality im-
pacts of the various residential space heating options. Specifically, it compares the
relative contributions of the space heating options to fine particulate emissions,
greenhouse gas emissions, and acid precipitation impacts. Approximately 6 quad-
rillion Btu (6. 5 x 10 to the 18th power joules) of energy was consumed for space
heating in 1997 in the U. S., representing about $45 billion in expenditures. There
were an estimated 99 million households in the U. S. in 1997, most of which required
some form of space heating. The major space heating energy options are natural
gas, fuel oil; kerosene, liquefied petroleum gas (LPG), electricity, coal, and wood.
Each of these residential space heating options has air quality issues associated with
it. To accurately compare national or global scale air quality impacts among energy
options, emissions from off-site production, processing, and transportation of the
energy need to be taken into consideration, along with the pollutants emitted locally
from individual residences. Residential wood combustion (RWC) meets 9% of the
Nation's space heating energy needs and utilizes a renewable resource. Wood is
burned regularly in about 30 million horr.es. Residential wood combustion is often
perceived as environmentally dirty due 10 emissions from older wood burners.
17. KEY WORDS ANO DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. cosati Field/Group
Pollution Emission
Residential Particles
Buildings Greenhouse Effect
Space Heating Gases
Wood Acidification
Combustion
Pollution Control
Stationary Sources
Residential Heating
Particulate
Acid Rain
Rain
13 B 14 G
13 M 04 A
13 A 04D
111, 07B.07C
04B
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report}
Unclassified
21. NO. OF PAGES
12
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
CPA Form 2220-1 (9-73)

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