APPENDIX W. EMISSIONS FACTORS FOR FUEL COMBUSTION FROM

NATURAL GAS, LPG, AND OIL-FIRED RESIDENTIAL FURNACES AND BOILERS

TABLE OF CONTENTS

W.1 OVERVIEW ........................................................ W-1

W.2 EMISSIONS FACTORS BY FUEL TYPE ................................. W-2

W.2.1 All Fuels: Carbon Dioxide ....................................... W-2

W.2.2 Natural Gas ................................................... W-2

W.2.2.1 Oxides of Nitrogen ..................................... W-2

W.2.2.2 Sulfur Dioxide ........................................ W-3

W.2.3 Fuel Oil #2 .................................................... W-3

W.2.3.1 Oxides of Nitrogen ..................................... W-3

W.2.3.2 Sulfur Dioxide ........................................ W-3

W.2.4 LPG ......................................................... W-4

W.2.4.1 Oxides of Nitrogen ..................................... W-4

W.2.4.2 Sulfur Dioxide ........................................ W-4

W.3 SUMMARY ......................................................... W-5

TABLES

Table W. 1. 1 Estimated National Average Emissions Factors for Household Fuel Combustion

of Natural Gas, Fuel Oil #2, and LPG ............................... W-1

 EE-RM/STD-01-350 COMMENT 164

APPENDIX W. EMISSIONS FACTORS FOR FUEL COMBUSTION FROM 

NATURAL GAS, LPG, AND OIL-FIRED RESIDENTIAL FURNACES AND BOILERS 

TABLE OF CONTENTS 

W.I OVERVIEW ........................................................ W-I 

W.2 EMISSIONS FACTORS BY FUEL TYPE ................................. W-2 

W.2.1 All Fuels: Carbon Dioxide ....................................... W-2 

W.2.2 Natural Gas ................................................... W-2 

W.2.2.1 Oxides of Nitrogen ..................................... W-2 

W.2.2.2 Sulfur Dioxide ........................................ W-3 

W.2.3 Fuel Oil #2 .................................................... W-3 

W.2.3.1 Oxides of Nitrogen ..................................... W-3 

W.2.3.2 Sulfur Dioxide ........................................ W-3 

W.2.4 LPG ......................................................... W-4 

W.2.4.1 Oxides of Nitrogen ..................................... W-4 

W.2.4.2 Sulfur Dioxide ........................................ W-4 

W.3 SUMMARY ......................................................... W-5 

TABLES 

Table W.l.I Estimated National Average Emissions Factors for Household Fuel Combustion 

of Natural Gas, Fuel Oil #2, and LPG ............................... W-I 

W-i 
APPENDIX W. EMISSIONS FACTORS FOR FUEL COMBUSTION FROM NATU RAL

GAS, LPG, AND OIL-FIRED RESIDENTIAL FURNACE AND BOILERS

W.1 OVERVIEW

The modified version of the National Energy Modeling System (NEMS) used for the furnace

and boiler energy-efficiency standards analysis, called NEMS-BT, comprehensively considers a

wide range of aspects of energy use. However, this model does not consider household emissions

of NO, and SO2 from the combustion of natural gas, residential heating fuel oil #2 (i.e., high-sulfur

distillate fuel oil), and LPG. Because an efficiency standard could result in changes in these

emissions, the Department has performed some elementary research to determine appropriate

emissions factors for CO2, NOR, and SO2 from household appliances. Specifically, this work focuses

on emissions rates from the use of furnace and boilers and is used to calculate emissions savings

from proposed efficiency standards. Because a majority of the savings from this standard are from

furnaces, emissions factors for furnaces are presented over small-scale boilers whenever both are

available.

This analysis attempts to verify that the emissions factors from the U.S. Environmental

Protection Agency (EPA) for C02, NOR, and SO2 from natural gas, fuel oil #2, and LPG combustion

are representative of the U.S.' The EPA cautions against the use of these emissions factors as

representative of actual emissions. Rather, they are to be used, and are used here, as general

approximations of national average emissions factors in order to calculate emissions savings that

result from proposed furnace and boiler energy-efficiency standards. This analysis compares the

EPA's emissions factors with those from other sources and with regional regulations.

Table W. 1.1 summarizes the emissions factor estimates for the three fuels of interest. The

values presented here are based on the EPA's assessment of combustion emissions (with the

exception of S02 from LPG, see discussion below). These emissions estimates represent an

approximate emissions factor for the U.S. as a whole. They are used, together with estimated

energy savings, to calculate end-use site emissions savings. The emissions factors discussed in this

analysis are represented as mass (g or kg) of the specific emission of interest per gigajoule (GJ) of

energy input to the furnace and boiler.*

. 0.454 kg = 1 lb; 1.055 GJ = 1 MBtu

W-1

 EE-RM/STD-01-350 COMMENT 164

APPENDIX W. EMISSIONS FACTORS FOR FUEL COMBUSTION FROM NATURAL 

GAS, LPG, AND OIL-FIRED RESIDENTIAL FURNACE AND BOILERS 

W.l OVERVIEW 

The modified version ofthe National Energy Modeling System (NEMS) used for the furnace 

and boiler energy-efficiency standards analysis, called NEMS-BT, comprehensively considers a 

wide range of aspects of energy use. However, this model does not consider household emissions 

of NO x and S02 from the combustion of natural gas, residential heating fuel oil #2 (i.e., high-sulfur 

distillate fuel oil), and LPG. Because an efficiency standard could result in changes in these 

emissions, the Department has performed some elementary research to determine appropriate 

emissions factors for CO2, NOx , and S02 from household appliances. Specifically, this work focuses 

on emissions rates from the use of furnace and boilers and is used to calculate emissions savings 

from proposed efficiency standards. Because a majority of the savings from this standard are from 

furnaces, emissions factors for furnaces are presented over small-scale boilers whenever both are 

available. 

This analysis attempts to verify that the emissions factors from the U.S. Environmental 

Protection Agency (EPA) for CO2, NOx, and S02 from natural gas, fuel oil #2, and LPG combustion 

are representative of the U.S. I The EPA cautions against the use of these emissions factors as 

representative of actual emissions. Rather, they are to be used, and are used here, as general 

approximations of national average emissions factors in order to calculate emissions savings that 

result from proposed furnace and boiler energy-efficiency standards. This analysis compares the 

EPA's emissions factors with those from other sources and with regional regulations. 

Table W.l.l summarizes the emissions factor estimates for the three fuels of interest. The 

values presented here are based on the EPA's assessment of combustion emissions (with the 

exception of S02 from LPG, see discussion below). These emissions estimates represent an 

approximate emissions factor for the U.S. as a whole. They are used, together with estimated 

energy savings, to calculate end-use site emissions savings. The emissions factors discussed in this 

analysis are represented as mass (g or kg) of the specific emission of interest per gigajoule (GJ) of 

energy input to the furnace and boiler. * 

* 0.454 kg = lIb; 1.055 GJ = 1 MBtu 

W-l 
Table W.1.1 Estimated National Average Emissions Factors for Household Fuel Combustion

of Natural Gas, Fuel Oil #2, and LPG

CO2

(kg/GJ)

NOx

(g/GJ)

SO2

(g/GJ)

Natural Gas 50.6 40 0

Fuel Oil #2 68.6 55 218

LPG 58.7 66 7

There are significant differences in state regulations, making it difficult to generalize about

localized emissions. For residential fuel oil combustion, stricter state standards exist in the

northeastern United States and southern California than elsewhere. State and local agencies like

southern California's South Coast Air Quality Management District (SCAQMD)2, the New Jersey

Department of Environmental Protection, and the New York Department of Environmental

Conservation have established regulations for residential fuel combustion emissions. These

regulations, however, are local to individual counties and do not apply to all regions in the Northeast

or even all of California.

W.2 EMISSIONS FACTORS BY FUEL TYPE

W.2.1 All Fuels: Carbon Dioxide

NEMS-BT tracks CO2 well, but factors are included here for completeness. The CO2

estimates in Table W.1.1 are based on EPA's assessment of CO2 combustion from natural gas, fuel

oil #2, and LPG use. Other sources of information include the U.S. DOE's Energy Information

Administration (EIA), Oregon State EPA, and the Gas Research Institute (GRI). All agree to within

± 2.0 percent of EPA's assessed estimate of CO2 emissions. EPA's CO2 emissions factors for

natural gas, fuel oil #2, and LPG combustion are therefore a reasonable evaluation of nationally

averaged CO2 emissions rates.

Carbon monoxide (CO) can be formed by incomplete carbon oxidization, causing a severe

health hazard. Carbon monoxide emissions only result from poorly functioning appliances, and

since NEMS-BT assumes that all furnaces and boilers are functioning properly, it is unlikely that

these emissions will change.

W.2.2 Natural Gas

W.2.2.1 Oxides of Nitrogen

Emissions of NOx that result from the combustion of natural gas from appliances are also

covered by regulations in some jurisdictions. The EPA's estimated NOx emissions factor of 40 g/GJ

from gas-fired furnaces is roughly equivalent to the regulation set by the state of New York. The

SCAQMD limits NO,, emissions to 40 g/GW from gas-fired residential furnaces, equivalent to

W-2

 EE-RM/STD-01-350 COMMENT 164

Table W.1.1 Estimated National Average Emissions Factors for Household Fuel Combustion 

of Natural Gas, Fuel on #2, and LPG 

CO2 NOx S02 

(kg/GJ) (g/GJ) (g/GJ) 

Natural Gas 50.6 40 0 

Fuel Oil #2 68.6 55 218 

LPG 58.7 66 7 

There are significant differences in state regulations, making it difficult to generalize about 

localized emissions. For residential fuel oil combustion, stricter state standards exist in the 

northeastern United States and southern California than elsewhere. State and local agencies like 

southern California's South Coast Air Quality Management District (SCAQMD)2, the New Jersey 

Department of Environmental Protection, and the New York Department of Environmental 

Conservation have established regulations for residential fuel combustion emissions. These 

regulations, however, are local to individual counties and do not apply to all regions in the Northeast 

or even all of California. 

W.2 EMISSIONS FACTORS BY FUEL TYPE 

W.2.1 All Fuels: Carbon Dioxide 

NEMS-BT tracks CO2 well, but factors are included here for completeness. The CO2 

estimates in Table W.l.l are based on EPA's assessment of CO2 combustion from natural gas, fuel 

oil #2, and LPG use. Other sources of information include the U.S. DOE's Energy Information 

Administration (EIA), Oregon State EPA, and the Gas Research Institute (GRI). All agree to within 

± 2.0 percent of EPA's assessed estimate of CO2 emissions. EPA's CO2 emissions factors for 

natural gas, fuel oil #2, and LPG combustion are therefore a reasonable evaluation of nationally 

averaged CO2 emissions rates. 

Carbon monoxide (CO) can be formed by incomplete carbon oxidization, causing a severe 

health hazard. Carbon monoxide emissions only result from poorly functioning appliances, and 

since NEMS-BT assumes that all furnaces and boilers are functioning properly, it is unlikely that 

these emissions will change. 

W.2.2 Natural Gas 

W.2.2.1 Oxides of Nitrogen 

Emissions of NO x that result from the combustion of natural gas from appliances are also 

covered by regulations in some jurisdictions. The EPA's estimated NOx emissions factor of 40 g/GJ 

from gas-fired furnaces is roughly equivalent to the regulation set by the state of New York. The 

SCAQMD limits NOx emissions to 40 g/GW from gas-fired residential furnaces, equivalent to 

W-2 
EPA's AP-42 estimate. The San Luis Obispo Air Pollution Control District also mandates the same

NOX limit from furnaces. The SCAQMD also provided performance test results from numerous

commercially available residential gas furnaces. In general, the emissions rates ranged from 35-40

g/GJ NO,, with some higher efficiency units emitting between 26-35 g/GJ NO,,. New Jersey's state

regulation mandates no more than 43 g/GJ NOX emissions from natural gas combustion in small

boilers and furnaces. The absence of regulations in other states suggests that most have emissions

rates comparable to the EPA's estimated value.

W.2.2.2 Sulfur Dioxide

SO2 emissions from natural gas combustion are assumed to be zero.

W.2.3 Fuel Oil #2

W.2.3.1 Oxides of Nitrogen

NOX formation in combustion processes is significantly more complex than the formation

of SO2 or CO2 . NOX can result from oxidization of N2 in the fuel, but the larger source is N2 in the

combustion intake. This process is sensitive to combustion chemistry , and therefore, quite variable.

It also implies that appliance design can lower NOX emissions . An added difficulty is that the

potential hazard of residential NOX emissions is hard to quantify . NOX is both an acid precipitation

and ozone (03)precursor, but because residential appliances are a relatively small and dispersed

(i.e., hard to monitor) source, these emissions tend to play a small role in NO, control strategies.

The 03 hazards of NOX emissions are highly variable both spatially and over time, as weather

conditions favor or disfavor 03 formation . One would, therefore, expect NOX emissions rules to vary

significantly across jurisdictions.

The value estimated by EPA of 55 g of NOX/GJ is for residential oil-fired furnaces.

Additional research into specific state regulations reveals good matches with EPA's emissions

factor: New Hampshire limits NOX emissions to 60 g/GJ for non-utility boilers and New York and

New Jersey regulations cap emissions at 52 g of NOX/GJ. These state limits confirm that EPA's

estimate can serve as a reasonable national average.

W.2.3.2 Sulfur Dioxide

Emissions of SO2 are a direct function of the sulfur content of the fuel . Assuming complete

combustion of sulfur to SO2 makes it easy to assess and compare emissions across data sources.

Individual state and county regulations limiting the amount of sulfur in residential fuel oil , however,

reveal substantial variability in SO2 emissions factors from EPA's estimate of 218g of S02/GJ of

fuel energy content for both residential furnaces and boilers. This is roughly equivalent to 0.5

percent sulfur content by weight using an emissions factor for fuel oil #2 of 43,950 g/GJ weight per

unit energy content. A straight multiplication of the fuel energy content and the percentage of sulfur

content in the fuel provide the emissions factor.

W-3

 EE-RM/STD-01-350 COMMENT 164

EPA's AP-42 estimate. The San Luis Obispo Air Pollution Control District also mandates the same 

NOx limit from furnaces. The SCAQMD also provided performance test results from numerous 

commercially available residential gas furnaces. In general, the emissions rates ranged from 35-40 

g/GJ NOx with some higher efficiency units emitting between 26-35 g/GJ NOx. New Jersey's state 

regulation mandates no more than 43 g/GJ NOx emissions from natural gas combustion in small 

boilers and furnaces. The absence of regulations in other states suggests that most have emissions 

rates comparable to the EPA's estimated value. 

W.2.2.2 Sulfur Dioxide 

S02 emissions from natural gas combustion are assumed to be zero. 

W.2.3 Fuel Oil #2 

W.2.3.1 Oxides of Nitrogen 

NOx formation in combustion processes is significantly more complex than the formation 

of S02 or CO2. NOx can result from oxidization ofN2 in the fuel, but the larger source is N2 in the 

combustion intake. This process is sensitive to combustion chemistry, and therefore, quite variable. 

It also implies that appliance design can lower NOx emissions. An added difficulty is that the 

potential hazard of residential NOx emissions is hard to quantify. NOx is both an acid precipitation 

and ozone (03) precursor, but because residential appliances are a relatively small and dispersed 

(i.e., hard to monitor) source, these emissions tend to playa small role in NOx control strategies. 

The 0 3 hazards of NOx emissions are highly variable both spatially and over time, as weather 

conditions favor or disfavor 0 3 formation. One would, therefore, expect NOx emissions rules to vary 

significantly across jurisdictions. 

The value estimated by EPA of 55 g of NO/GJ is for residential oil-fired furnaces. 

Additional research into specific state regulations reveals good matches with EPA's emissions 

factor: New Hampshire limits NOx emissions to 60 g/GJ for non-utility boilers and New York and 

New Jersey regulations cap emissions at 52 g ofNO/GJ. These state limits confirm that EPA's 

estimate can serve as a reasonable national average. 

W.2.3.2 Sulfur Dioxide 

Emissions ofS02 are a direct function of the sulfur content of the fuel. Assuming complete 

combustion of sulfur to S02 makes it easy to assess and compare emissions across data sources. 

Individual state and county regulations limiting the amount of sulfur in residential fuel oil, however, 

reveal substantial variability in S02 emissions factors from EPA's estimate of218g ofSO/GJ of 

fuel energy content for both residential furnaces and boilers. This is roughly equivalent to 0.5 

percent sulfur content by weight using an emissions factor for fuel oil #2 of 43,950 g/GJ weight per 

unit energy content. A straight multiplication of the fuel energy content and the percentage of sulfur 

content in the fuel provide the emissions factor. 

W-3 
In the state of New York, SO2 emissions limits range from 88-659 g/GJ depending on the

county. In New Hampshire, the emissions rate of SO2 from high-sulfur distillate fuel oil combustion

cannot exceed 176 g/GJ. In Maine and Michigan, the regulations are higher than EPA's assessment,

limiting SO2 emissions from fuel oil to 500 g of S02/GJ of heat input. Such broad ranges and

varying limits in certain regions are a strong argument for using EPA's averaged national value over

a regionally weighted average incorporating the various state and county regulations.

Comparing the sulfur content of fuel oil from different refineries also demonstrates regional

variability. Most sources were obtained through online websites detailing product specifications.

Mobil Corporation's residential heating fuel oil (#2 high-sulfur) for most states contains a maximum

0.5% sulfur by mass (219 g of S02/GJ of heat input), which is very close to EPA's emissions factor.

Mobil also markets fuel with lower sulfur content to some regions in the Northeast. For example,

Mobil's lowest sulfur content residential heating fuel oil contains 0.2 percent sulfur by weight (88

g/GJ), as required in New York City, Philadelphia, parts of Delaware, and most of New Jersey.

Other regional regulations adhered to by Mobil are 132 g/GJ for most of Pennsylvania and parts of

New Jersey, a limit of 127 g of S02/GJ of heat input for the state of Illinois, and an SO2 emissions

factor of 145 g/GJ in Massachusetts. The sulfur contents of distillate fuel oil from Chevron, Phillips

66, and the American Society for Testing and Materials (ASTM) exactly match EPA's estimate,

substantiating the use of the latter for the analysis. Considerable variation does exist among counties

and states, especially in the Northeast. Nonetheless, EPA provides a reasonable estimate of

emissions from residential oil-fired furnaces and boilers that are representative of the national

average.

W.2.4 LPG

W.2.4.1 Oxides of Nitrogen

Although NES results are presented for LPG, EPA estimates emissions for only propane and

butane, fuels within the LPG family of gases. In the United States, the composition of LPG is

typically 90 percent propane (C3H8) by liquid volume, 5 percent propylene (C3H6), and 2.5 percent

butane (C4H10).3'4 This analysis uses EPA's propane emissions estimate to verify its comparability

with LPG combustion or determines a more suitable estimate from other sources that best represents

LPG emissions rates.

EPA estimates an emissions factor of 66 g of NOX/GJ of energy input from propane-fired

furnaces and boilers, which is slightly higher than the natural gas estimate. The University of New

Hampshire's Energy Office estimates an emissions factor of 43 g/GJ from LPG combustion for the

state of New Hampshire. In contrast, the state of New Jersey's EPA establishes an 86 g/GJ

emissions factor. Both sources, therefore, support EPA's national assessment of NOX emissions

from residential propane combustion.

W-4

 EE-RM/STD-01-350 COMMENT 164

In the state of New York, S02 emissions limits range from 88-659 g/GJ depending on the 

county. In New Hampshire, the emissions rate ofS02 from high-sulfur distillate fuel oil combustion 

cannot exceed 176 g/GJ. In Maine and Michigan, the regulations are higher than EP A's assessment, 

limiting S02 emissions from fuel oil to 500 g of SO/GJ of heat input. Such broad ranges and 

varying limits in certain regions are a strong argument for using EPA's averaged national value over 

a regionally weighted average incorporating the various state and county regulations. 

Comparing the sulfur content of fuel oil from different refineries also demonstrates regional 

variability. Most sources were obtained through online websites detailing product specifications. 

Mobil Corporation's residential heating fuel oil (#2 high-sulfur) for most states contains a maximum 

0.5% sulfur by mass (219 g ofSO/GJ of heat input), which is very close to EPA's emissions factor. 

Mobil also markets fuel with lower sulfur content to some regions in the Northeast. For example, 

Mobil's lowest sulfur content residential heating fuel oil contains 0.2 percent sulfur by weight (88 

g/GJ), as required in New York City, Philadelphia, parts of Delaware, and most of New Jersey. 

Other regional regulations adhered to by Mobil are 132 g/GJ for most of Pennsylvania and parts of 

New Jersey, a limit of 127 g of SO/GJ of heat input for the state of Illinois, and an S02 emissions 

factor of 145 g/GJ in Massachusetts. The sulfur contents of distillate fuel oil from Chevron, Phillips 

66, and the American Society for Testing and Materials (ASTM) exactly match EPA's estimate, 

substantiating the use of the latter for the analysis. Considerable variation does exist among counties 

and states, especially in the Northeast. Nonetheless, EPA provides a reasonable estimate of 

emissions from residential oil-fired furnaces and boilers that are representative of the national 

average. 

W.2.4 LPG 

W.2.4.1 Oxides of Nitrogen 

Although NES results are presented for LPG , EPA estimates emissions for only propane and 

butane, fuels within the LPG family of gases. In the United States, the composition of LPG is 

typically 90 percent propane (C3Hg) by liquid volume, 5 percent propylene (C3H6), and 2.5 percent 

butane (C4HIO).3,4 This analysis uses EPA's propane emissions estimate to verify its comparability 

with LPG combustion or determines a more suitable estimate from other sources that best represents 

LPG emissions rates. 

EPA estimates an emissions factor of 66 g of NOJGJ of energy input from propane-fired 

furnaces and boilers, which is slightly higher than the natural gas estimate. The University of New 

Hampshire's Energy Office estimates an emissions factor of 43 g/GJ from LPG combustion for the 

state of New Hampshire. In contrast, the state of New Jersey's EPA establishes an 86 g/GJ 

emissions factor. Both sources, therefore, support EPA's national assessment of NO x emissions 

from residential propane combustion. 

W-4 
W.2.4.2 Sulfur Dioxide

The sulfur content of LPG is very lows, although a few regulations exist in certain parts of

the country. EPA's SO2 emissions estimate is derived from the sulfur content of the propane fuel.

With 90% of LPG comprised of propane, the EPA's propane emissions factor is a reasonable value

for LPG emissions rates. Under the New Hampshire Department of Environmental Services (DES)

regulation, the maximum sulfur content allowable is 13.3 g/GJ of SO, from LPG combustion. The

San Diego County Air Pollution Control District enforces a stricter limit of only 8.8 g of S02/GJ of

energy input using EPA's recommended value. Both the ASTM and Santa Barbara County Air

Pollution Control District specify a sulfur standard of 0.0185 percent sulfur by weight, which

approximates an emissions factor of 4.0 g of S02/GJ of energy input. This calculation is based on

an LPG weight per unit energy of 21,756 g/GJ. Even lower, Nett Technologies Inc. estimates a

0.012 percent sulfur content by mass LPG average for the United States as well as Canada, which

is approximately 2.6 g of SO2/GJ of heat input.

The wide range of emissions factors for SO2 makes it difficult to determine a representative

estimate for the emissions factor and the very small net effect of any energy-efficiency standard

argue against making a significant research effort. The obtained estimates range in magnitude from

approximately 4 to 13 g/GJ of energy input. The statistical average or arithmetic mean of these four

estimates is 7.2 g/GJ, the value provided in Table W.1.1. The averaged emissions factor estimate

of 7.2 g/GJ energy input is reasonable to explain three of the five sources presented and suitably

accounts for the average among the two extreme estimates. Table W.1.1 therefore adequately

represents national SO2 emissions from residential LPG combustion.

W.3 SUMMARY

This investigation of emissions factors from natural gas-, fuel oil-, and LPG-fired residential

furnaces and boilers indicates that using the values estimated by EPA's AP-42 is a robust and

credible basis for analysis with NES output. This analysis indicates that regulations at the state and

county level, especially in the northeastern region of the United States, are generally not good

estimators of the national average set forth by the EPA AP-42 report. This is especially true for SO2

emissions factors from fuel oil combustion where individual state and county regulations are highly

variable. Thus, although it is worthwhile examining regional legislation to support the national

average, this analysis demonstrates the complexity that would be required to establish a weighted

regional calculation for each emission. The EPA's own lack of data on the sulfur content of LPG

made it difficult to derive a nationally representative emissions factor for the country as a whole.

External sources were therefore incorporated in the Table W. 1.1 estimate for SO2 emissions from

LPG combustion.

 EE-RM/STD-01-350 COMMENT 164

W.2.4.2 Sulfur Dioxide 

The sulfur content of LPG is very lows, although a few regulations exist in certain parts of 

the country. EPA's S02 emissions estimate is derived from the sulfur content of the propane fuel. 

With 90% of LPG comprised of propane, the EPA's propane emissions factor is a reasonable value 

for LPG emissions rates. Under the New Hampshire Department of Environmental Services (DES) 

regulation, the maximum sulfur content allowable is 13.3 g/GJ of S02 from LPG combustion. The 

San Diego County Air Pollution Control District enforces a stricter limit of only 8.8 g of SOiGJ of 

energy input using EPA's recommended value. Both the ASTM and Santa Barbara County Air 

Pollution Control District specify a sulfur standard of 0.0185 percent sulfur by weight, which 

approximates an emissions factor of 4.0 g of SOiGJ of energy input. This calculation is based on 

an LPG weight per unit energy of 21 ,756 g/GJ. Even lower, Nett Technologies Inc. estimates a 

0.012 percent sulfur content by mass LPG average for the United States as well as Canada, which 

is approximately 2.6 g of SO/GJ of heat input. 

The wide range of emissions factors for S02 makes it difficult to determine a representative 

estimate for the emissions factor and the very small net effect of any energy-efficiency standard 

argue against making a significant research effort. The obtained estimates range in magnitude from 

approximately 4 to 13 g/GJ of energy input. The statistical average or arithmetic mean of these four 

estimates is 7.2 g/GJ, the value provided in Table W.I.I. The averaged emissions factor estimate 

of 7.2 g/GJ energy input is reasonable to explain three of the five sources presented and suitably 

accounts for the average among the two extreme estimates. Table W.I.l therefore adequately 

represents national S02 emissions from residential LPG combustion. 

W.3 SUMMARY 

This investigation of emissions factors from natural gas-, fuel oil-, and LPG-fired residential 

furnaces and boilers indicates that using the values estimated by EPA's AP-42 is a robust and 

credible basis for analysis with NES output. This analysis indicates that regulations at the state and 

county level, especially in the northeastern region of the United States, are generally not good 

estimators of the national average set forth by the EPA AP-42 report. This is especially true for S02 

emissions factors from fuel oil combustion where individual state and county regulations are highly 

variable. Thus, although it is worthwhile examining regional legislation to support the national 

average, this analysis demonstrates the complexity that would be required to establish a weighted 

regional calculation for each emission. The EPA's own lack of data on the sulfur content of LPG 

made it difficult to derive a nationally representative emissions factor for the country as a whole. 

External sources were therefore incorporated in the Table W.I.I estimate for S02 emissions from 

LPG combustion. 

W-5 
REFERENCES

U.S. Environmental Protection Agency, Compilation ofA ir Pollutant Emission Factors, AP42, Fifth Edition, Volume I: Stationary Point and Area Sources, 1998. (Posted October)

<htlp://www.epa.gov/ttn/chief/ap42.html>

2. South Coast Air Quality Management District, Rule 1121: Control ofNitrogen Oxides From

Residential Type, Natural Gas-Fired Water Heaters, 1995. March. <http://www.agmd.gov/>

3. U.S. Department of Energy, U.S. Hemispheric Clean Cities Program, 1994.

<http://www.eere.energy.gov/cleancities/>

4. NewJersey State Department of Environmental Protection, New Jersey Administrative Code,

Title 7, Chapter 27, Subchapter 19: Control and Prohibition ofAir Pollution from Oxides

of Nitrogen; 7:27-19.7 Non-Utility Boilers and other indirect heat exchangers, September

1993. <http://www.state .nj.us/dep/agm/2719968 .htm#Boilers>

5. U.S. Environmental Protection Agency, Compilation ofA irPollutant Emission Factors, AP42, Fifth Edition, Volume I: Stationary Point and Area Sources, Chapter 1, External

Combustion Sources, 1998. (Posted October) <http://www.epa. gov/ttn/chief/ap42c l .html>

 EE-RM/STD-01-350 COMMENT 164

REFERENCES 

1. U.S. Environmental Protection Agency, Compilation o/Air Pollutant Emission Factors, AP42, Fifth Edition, Volume I: Stationary Point and Area Sources, 1998. (Posted October) 

<http://www.epa.gov/ttnlchief/ap42.html> 

2. South Coast Air Quality Management District, Rule 1121: Controlo/Nitrogen Oxides From 

Residential Type, Natural Gas-Fired Water Heaters, 1995. March. <http://www .aqmd. gov/> 

3. U.S. Department of Energy, Us. Hemispheric Clean Cities Program, 1994. 

<http://www.eere.energy.gov/cleancities/> 

4. New Jersey State Department of Environmental Protection, New Jersey Administrative Code, 

Title 7, Chapter 27, Subchapter 19: Control and Prohibition of Air Pollution/rom Oxides 

o/Nitrogen; 7:27-19.7 Non-Utility Boilers and other indirect heat exchangers, September 

1993. <http://www.state.nj.us/dep/aqml2719968.htm#Boilers> 

5. U.S. Environmental Protection Agency, Compilation 0/ Air Pollutant Emission Factors, AP42, Fifth Edition, Volume I: Stationary Point and Area Sources, Chapter 1, External 

Combustion Sources, 1998. (Posted October) <http://www .epa. gOY /ttnl chief/ ap42c l.html> 

W-6