Using WARM Emission Factors for Materials and

Pathways Not in WARM

EPA's Waste Reduction Model (WARM) recognizes 54 material types, and that number continues to
grow. However, users may still find that some materials and pathways of interest to them are not
represented in the model. In such cases, WARM users often apply WARM factors for materials that
seem similar to the non-WARM material in which they are interested. This document discusses some of
the limitations of using WARM materials as proxies for non-WARM materials, and provides EPA-
approved WARM proxies for some commonly-requested non-WARM materials.

Example uses of proxies

Users may wish to use WARM factors as proxies in three primary situations:

1.	To model a material that is not in WARM, but is similar to a material that is in WARM. For
example, using the personal computer recycling factor to represent recycling of all electronics.

2.	To model a different recycling pathway for a WARM material. For example, modeling drywall
recycled into fertilizer instead of a mix of new drywall and agricultural products.

3.	To model a different material that follows a similar recycling pathway to a material that is
recycled in WARM. For example, using the concrete-to-aggregate recycling factor to model
other materials recycled as aggregate.

The suitability of proxies for any of these purposes will vary widely, depending on the specific life-cycle
stages of the material and its intended proxy.

When are proxies okay and not okay to
use?

When considering proxies, users should remember
that similarity in materials' physical properties does
not necessarily indicate that life-cycle energy use
and greenhouse gas (GHG) emissions are the same.

The processes used to create them, or manage
them at their end-of-life, could be quite different.

For example, fiberglass insulation may share many
physical properties with glass bottles (i.e., both are
comprised largely of glass), but the processes used
to make these materials, and to recycle them, are
very different. Therefore, the recycling factor for
glass bottles may not be a good proxy for recycling
fiberglass.

Conversely, furnace slag and concrete may seem to
be less closely related, but the concrete recycling
factor is an acceptable proxy for recycling furnace

Why isn't my material in WARM?

EPA is committed to providing high-quality
emission factors in WARM. Factors are developed
using life-cycle inventory data from published
studies or industry-specific contacts, along with
robust analyses, and undergo an internal and
expert review process. Users can therefore be
confident about the quality of WARM estimates.

EPA is continually adding new materials to WARM;
however, developing emission factors takes some
time and is dependent on data availability. In
2010, EPA developed a new process for prioritizing
materials to add; this process relies heavily on
input from EPA Regions and other stakeholders,
and is intended to help meet the needs of the
majority of WARM users.

Sometimes, EPA would like to add a certain
material to WARM, but the necessary data are
simply not available. To maintain the integrity of
WARM, EPA declines to develop factors when data
and methodologies do not meet EPA's standards.

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slag into aggregate. In this situation, the recycling pathways are fairly similar, partly because both offset
virgin aggregate production.

To be a good proxy, materials should be similar in the processes related to:

•	How materials are acquired;

•	How the product itself is manufactured;

•	The manner in which the materials are collected at their end-of-life; and

•	The materials and processes that are offset when the materials are recycled.

EPA has developed a list of acceptable proxies, included in Appendix A.1 To help illustrate how some
materials may follow the life-cycle pathways of proxies more closely than others, EPA has also created a
set of example diagrams that illustrate where along the life-cycle pathway the proxy pathways diverge
from the WARM pathways. Please see Appendix B.

What are the benefits and drawbacks of using proxies?

An advantage of using proxies is that they help extend the use of WARM to cover more materials and
pathways than those currently in the model.

Users should be aware of the drawbacks of proxy use, however. Although EPA strives to provide high-
quality emission factors in WARM, there is already some uncertainty inherent in the factors due to the
challenges of providing one-size-fits-all factors. Processes, transportation distances, landfill operations,
etc. can vary by location and facility, and WARM cannot account for all these variations. Using proxies
adds further (and potentially significant) uncertainty to
WARM calculations, due to differences in the materials'
life cycles.

Why aren't more recycling pathways
modeled in WARM?

Differences in processes may seem relatively minor on
the surface, but they can have large impacts on the
calculations. For example, if manufacturing processes
represent a particularly energy-intensive part of an
emission factor, then differences in the way materials
are produced—such as using different fuel types, or
relying on some different input materials— can
significantly affect the resulting emissions.

In cases where the life-cycle stages of a WARM material
are not a close match to the material of interest, it may
be better to not model that material at all.

You may be wondering what the benefits are
for recycling, for example, glass bottles into
aggregate used in kitchen countertops. You
look to WARM and find that it indeed
models recycling of glass bottles....but only
to new glass bottles. Sound familiar?

Users sometimes wish to see more options
for material recycling fates. It is WARM
convention, however, to provide only one
set of emission factors for each material.
Recycled materials are often aggregated at
recycling centers, and distributed for use in
various pathways. The person deciding to
recycle often has little control over (or even
knowledge of) how the recycled material is
ultimately used. Therefore, WARM recycling
factors aim to represent the common end-
uses of the recycled materials.

1 Use of these proxies may help WARM users understand the approximate GHG impacts of non-WARM materials or
pathways. However, users should be aware that estimates developed using proxies may have a large degree of
uncertainty associated with them. The list of acceptable proxies were developed using expert judgment, and
proxies have not been quantitatively assessed or undergone extensive review.

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Appendix A: List of Acceptable WARM Proxies

This table presents a set of acceptable material proxies; however, the list is not comprehensive. If a proxy does not appear on the list, it does not
necessarily mean that it is unacceptable; please contact orcrWARMquestionsffiepa.gov if you have questions about the suitability of a proxy not
listed here.

Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)

Aggregate

Concrete

All available

Very Good

This proxy is suitable for any source of aggregate used to replace
virgin aggregate.

Concrete is a high-volume building material produced by mixing
cement, water, and coarse and fine aggregates. In WARM, concrete is
assumed to be recycled into aggregate, so the GHG benefits from the
avoided emissions associated with mining and processing aggregate.
However, WARM currently does not have data for the source
reduction of concrete.

Note: Steel slag and furnace slag used as aggregate would not require
the same crushing processes as concrete or other materials recycled
into aggregate, so this proxy would be considered "Acceptable" when
modeling those materials.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)









In WARM, the aluminum ingot energy and GHG emissions factors
could be used as a conservative proxy for representing aluminum
materials other than aluminum cans, including electrical transmission
and distribution wires, other electrical conductors, some extruded
aluminum products, and/or aluminum product cuttings, joinings and
weldings. The aluminum ingot material is also an acceptable proxy for
products where aluminum alloy is used but the fabrication techniques
are not clear or in a mixture. For instance, aluminum used in
consumer durable products such as home appliances, computers, and
electronics.

C&D Aluminum and
other aluminum
products

Aluminum Ingot

All available

Acceptable

However, using the aluminum ingot material type as a proxy for the
aluminum materials mentioned above does not factor in the energy
and emissions associated with the additional processing of aluminum
ingot to produce a final aluminum product, which are likely to be
quite significant. Thus, the resultant energy and GHG emissions
impacts of managing aluminum products as represented by the
WARM aluminum ingot factors likely underestimate the true impacts.

C&D Steel

Steel Cans

All available

Acceptable

The LCI data used to construct the "steel cans" material type
represent three-piece welded cans produced from sheet steel which
is made in a blast furnace and basic oxygen furnace (for virgin cans)
or electric arc furnace (for recycled cans). Therefore, it may not
exactly represent other Steel types but is an acceptable proxy.

Cabinets and doors

Wood Flooring

All available

Acceptable

Although the "Dimensional Lumber" material type could be used as a
proxy, the "wood flooring" material type incorporates a hardwood
flooring production stage, which may be similar to the cabinet or
door processing stage.

Clean wood/pallets

Dimensional
Lumber

All available

Very Good

The Dimensional Lumber material type is representative of wood
used for containers, packaging, and building and includes crates,
pallets, furniture and dimensional lumber like two-by-fours.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)

Coated paper

Magazines/Third-
class Mail

All available

Good

Third-class Mail is now called Standard Mail by the U.S. Postal Service
and includes catalogs and other direct bulk mailings such as
magazines, which are made of coated, shiny paper.

Crumb rubber in
asphalt binder

Tires

All available

Good

To the extent that recycled tires are used to displace ground rubber in
asphalt binder, this is a good proxy.

Drywall-to:
animal bedding,
compost,
fertilizer,
soil amendment,
etc.

Dry wall

All available

Very Good

The drywall emission factor models the displacement of virgin
gypsum by recycled drywall, for both agricultural and new drywall
purposes. Assuming that the pathway recommended here represents
displacement of virgin gypsum or recycled paper, the drywall factors
are a Very Good proxy.









This proxy is suitable for plastic electronic media materials, such as
compact discs.

Electronic Media
(CDs)

Mixed Plastics

All available

Acceptable

Since CDs are comprised largely of polycarbonate plastic, this is a
suitable proxy. However, the 'mixed plastics' may cover different
types of plastic not used for CDs.

Electronics

Personal Computers

All available

Acceptable

Electronics and PCs have similar components. However, the exact
make-up of a given electronics can be very different than a PC,
depending on the type of product.

Fats, oils, and
greases

Food Waste

Source
Reduction,
Landfilling,
Combustion

Acceptable

Upstream emissions from producing "fats, oils, and greases" may vary
significantly depending on the material(s) from which they are
derived. It is likely that "fats, oils, and greases" behave differently in
landfills as oppose to other food wastes. Also, composting is not a
suitable pathway for "fats, oils, and greases".

Furnace slag-to-
cement

Fly Ash

All available

Good

Since fly ash is also a byproduct that replaces cement, it can be used
as a proxy in this situation.

High-grade Paper

Office Paper

All available

Very Good

Office paper represents paper made from uncoated bleached
chemical pulp.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)

Lamb and veal

Beef

All available

Acceptable

Emissions from production of different animal-based products can
vary significantly based on differences in livestock characteristics,
feed requirements, and production practices. As ruminants, lamb and
veal production is likely to involve similar upstream energy and GHG
emissions as beef production, making the beef factor an acceptable
proxy for lamb and veal at this time.

MDF Cabinets for
reuse

Medium-density
Fiberboard

Source
Reduction

Acceptable

Although the MDF material type in WARM will not incorporate the
actual production of the cabinets themselves, using the source
reduction pathway for MDF should be a good proxy for reuse of MDF
cabinets.

Metal (type
unknown)

Mixed Metals

All available

Good

Mixed metals are made up of 39% aluminum cans and 61% steel cans
(based on 2010 data—this percentage is updated annually). This is an
accurate proxy if the unknown metal type is a mixture of aluminum
and steel.









Office mixed paper is assumed to be 21% newspaper, 5% corrugated
containers, 36% magazines/third-class mail, and 38% office paper.

Mixed Paper
(primarily from
offices)

Mixed Paper-
Office Paper
Definition

All available

Good/Very Good

If the mix of paper is close to this definition, then the proxy is Very
Good. If the mix of paper does not resemble this definition closely,
then the proxy is Good.









Residential mixed paper is assumed to be 23% newspaper, 53%
corrugated containers, 10% magazines/third-class mail, and 14%
office paper.

Mixed Paper

(primarily

residential)

Mixed Paper-

Residential

Definition

All available

Good/Very Good

If the mix of paper is close to this definition, then the proxy is Very
Good. If the mix of paper does not resemble this definition closely,
then the proxy is Good.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)









Mixed paper is assumed to be 24% newspaper, 48% corrugated
containers, 8% magazines/third-class mail, and 20% office paper.

Mixed Paper (type
unknown)

Mixed Paper-
Broad Definition

All available

Good/Very Good

If the mix of paper is close to this definition, then the proxy is Very
Good. If the mix of paper does not resemble this definition closely,
then the proxy is Good.

Organics (type
unknown)

Mixed Organics

All available

Good

Mixed organics are made up of 51% food scraps and 49% yard
trimmings (based on 2010 data—this percentage is updated
annually).

Other Ferrous
Metals

Steel Cans

All available

Good

Steel cans represent three-piece welded cans produced from sheet
steel which is made in a blast furnace and basic oxygen furnace (for
virgin cans) or electric arc furnace (for recycled cans). Steel is one
type of ferrous metal (i.e., a metal that contains the element iron)
and is the only ferrous metal modeled in WARM.

Other Non-Ferrous
Metals

(Copper Wire * 0.5)
+ (Aluminum Ingot
* 0.5)

All available

Good

Aluminum and copper are two types of non-ferrous metals. Other
non-ferrous metals include lead and tin. To the extent that the
material contains only copper and aluminum, this is a good proxy.

Other processed or
prepared foods

Food Waste

All available

Acceptable

Many processed or prepared food products are likely to contain a
mixture of individual food waste components available in WARM
(grains, dairy products, fruits and vegetables, beef, and poultry) and
others not currently modeled in WARM (caloric sweeteners, added
fats and oils). A wide variety of ingredients are used in the many
processed and prepared foods available in the United States;
therefore, estimating upstream energy and GHG emissions from an
individual food product in WARM involves a large degree of
uncertainty. Due to this uncertainty, the "Food Waste" factor is an
acceptable proxy at this time.

Other Yard Waste

Yard Trimmings

All available

Very Good

Yard trimmings are assumed to be 50% grass, 25% leaves, and 25%
tree and brush trimmings from residential, institutional, and
commercial sources.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)

Plastic (resin
unknown)

Mixed Plastics

All available

Good

Mixed plastics are made up of 50% HDPE and 50% PET plastic based
on the weighted average of the amount of total plastic recovered.

Plywood

Medium-density
Fiberboard

All available

Very Good

The MDF material type is a panel product that consists of wood chips
pressed and bonded with a resin. Plywood is an example of an MDF
material.

Polypropylene

Mixed Plastics

Recycling

Acceptable

Although polypropylene is currently modeled in WARM, not enough
data were available to develop recycling emission factors. For
recycling, use mixed plastics, which are made up of 50% HDPE and
50% PET plastic based on the weighted average of the amount of
total plastic recovered.. Although this is a different resin, it is an
acceptable proxy for now.

Polystyrene

Mixed Plastics

Recycling

Acceptable

Although polystyrene is currently modeled in WARM, not enough
data were available to develop recycling emission factors. For
recycling, use mixed plastics, which are made up of 50% HDPE and
50% PET plastic based on the weighted average of the amount of
total plastic recovered. Although this is a different resin, it is an
acceptable proxy for now.

Pork

Food Waste

All available

Acceptable

Pork production is likely to require less upstream energy and GHG
emissions than beef production but is somewhat more emissions-
intensive than poultry production. Based on a survey2 of available
estimates of life-cycle production emissions for pork, the emissions
are within the same order of magnitude as the "Food Waste" factor in
WARM. Therefore, although the food waste factor represents a mix
of foods and does not have a direct connection to pork production
processes, this is an acceptable proxy to develop rough "order of
magnitude" estimates for pork wastes.

2 Hammerschlag, K. and K. Venkat. 2011. "Meat Eater's Guide to Climate Change & Health - Life Cycle Assessments: Methodology & Results." Environmental Working Group. Retrieved from:
http://static.ewg. org/ reports/2011/meateaters/pdf/methodology_ewg_meat_eaters_guide_to_health_and_climate_2011.pdf?_ga=l. 144155635.732812262.1425505183.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)







Relative









Suitability* of









Proxy





Associated WARM



(Very Good, Good,



Material

Emission Factor

Pathway(s)

Acceptable)

Comments (why it is ranked the way it is)









Although PVC is currently modeled in WARM, not enough data were









available to develop recycling emission factors. For recycling, use









mixed plastics, which are made up of 50% HDPE and 50% PET plastic









based on the weighted average of the amount of total plastic









recovered. Although this is a different resin, it is an acceptable proxy

PVC/Vinyl

Mixed Plastics

Recycling

Acceptable

for now.









Seafood production is likely to require less upstream energy and GHG









emissions than beef production but is somewhat more emissions-









intensive than poultry production. Based on a survey2 of available









estimates of life-cycle production emissions for seafood has found









that the emissions are within the same order of magnitude as the









"Food Waste" factor in WARM. Therefore, although the food waste









factor represents a mix of foods and does not have a direct









connection to seafood production processes, this is an acceptable









proxy to develop rough "order of magnitude" estimates for seafood

Seafood

Food Waste

All available

Acceptable

wastes

Tires-to-fuel

Tires

Combustion

Very Good

This is modeled in the combustion pathway for tires.

Turkey and other







The "poultry" factor in WARM is based on broiler chicken product,

non-chicken







but due to similarities in production practices, it is a good proxy for

poultry

Poultry

All available

Acceptable

other poultry meats beyond broiler chicken.









This category is too broad to assess the materials it encompasses, but

Various/general







mixed recyclables will likely cover many of the materials included in

materials

Mixed Recyclables

All available

Acceptable

this category.









Lumber includes wood used for containers, packaging, and building



Dimensional





and includes crates, pallets, furniture and dimensional lumber like

Wood (General)

Lumber

All available

Acceptable

two by fours.

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Available WARM Proxies, and Relative "Suitability" of that Proxy (based on expert judgment)

Material

Associated WARM
Emission Factor

Pathway(s)

Relative
Suitability* of
Proxy

(Very Good, Good,
Acceptable)

Comments (why it is ranked the way it is)

Wood for fuel

Combustion factor
for dimensional
lumber

Combustion

Very Good

Dimensional lumber is a very good proxy if the wood is being
combusted to generate electricity. Because the emission factor
accounts for avoided utility emissions, it would NOT be a good proxy
for other wood burning purposes, such as for heating a home.
Depending on the type of wood being burned, MDF or wood flooring
could also be suitable proxies.

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Appendix B: Life-cycle Illustrations of Proxies

Life Cycle of Concrete
Possible Proxy for Other* Materials Recycled into Aggregate

Raw Material Acquisition,
Processing, Transport, &
Concrete Manufacture

•"Other" materials may include, for
example, steel slag and furnace slag

Raw Material Acquisition,
Processing, & Transport
(Virgin Manufacture Only)

End of Life

Removal and Crushing of Concrete
into Aggregate: Recycling Offsets
Virgin Aggregate Manufacture

Collection and Preparation of "Other"

Material into Aggregate: Recycling
Offsets Virgin Aggregate Manufacture

Collection/Transport to Landfill

Landfilling

Key



.ife-Cycle Stages That
Are 6HG Sources
(Positive Emissions)

-4



End-of-Life Pathways
in WARM

1



Steps Not Included in
WARM

Not Modeled for This
Material and/or Not
Recommended for
Proxy Use



Proxy Material
Not Modeled in
WARM

Limitations of using Concrete as a proxy for Materials
Recycled into Aggregate:

©Proxy use assumes that collection and preparation (e.g.,
crushing) of materials recycled into aggregate requires similar
energy use and results in similar emissions as removal and
crushing of concrete.

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Life Cycle of Steel Cans and Aluminum Ingot
Possible Proxy for C&D Steel and C&D Aluminum

Raw Material Acquisition,
Processing, & Transport
(Virgin Manufacture Only)

C&D Steel & Alum.
Manufacture

0

Limitations of using Steel and Aluminum Ingot as a
proxy for C&D Steel and Aluminum:

0

Steel Can and Alum.
Ingot Manufacture:
Recycling Offsets
Virgin Manufacture

Proxy use assumes that C&D Steel and Aluminum manufacture
requires similar energy use, and results in similar emissions
generation, as Steel and Aluminum Ingot manufacture.

Transport to
Recycled Metals
Manufacturing
Facility

Other Aluminum
End-products

Steel Cans

and
Aluminum
Ingot

End of Life

Collection/
Transport to
Recycling Facility

Collection/
Transport to
Combustion Facility

Collection/
Transport to Landfill

Not
Modeled

Recycled Metals
Sorting and
Processing

Landfilling

Steel (majority)
recovered for
recycling.
No aluminum
assumed to be
recovered.

Ash Residue
Transport to
Landfill

Life-Cycle Stages That

Result in Both
Positive and Negative
Emissions

Steps Not Included in
WARM

Not Modeled for This
Material

Proxy Material
Not Modeled in
WARM



Ash Residue
Landfilling

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Life Cycle of Wood Flooring
Possible Proxy for Wooden Cabinets and Doors

Raw Material Acquisition,
Processing, & Transport

Transport to
Retail Facility

Limitations of using wood flooring as a
proxy for cabinets/doors:

0 Proxy use assumes that cabinets/doors are made
from hardwood, not softwood. This assumption
has a significant impact on the emission factors.

©Proxy use assumes that cabinet/door manufacture
requires similar energy use, and results in similar
emissions generation, as wood flooring
manufacture.

Extraction, Grinding

&Transport to
Combustion Facility

Extraction/
Transport to Landfill

Not
Modeled

Not
Modeled

Combustion

Landfilling

Ash Residue
Landfilling



Life-Cycle Stages That
Resuft in GHG Storage
or Offsets (Negative
Emissions)

Life-Cycle Stages That

Result in Both
Positive and Negative
Emissions

Not Modeled for This
Material

Proxy Material
Not Modeled in
WARM

J

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