United States Department of Agriculture

Forest 

Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-951 July 

2017

Life Cycle Assessment of Wood 

Energy for Residential Heating—

Opportunities for Wood Pellet 

Production in Southeast Alaska

Allen M. Brackley, David L. Nicholls, Maureen Puettmann, and Elaine Oneil
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Authors

Allen M. Brackley is a research forester and David L. Nicholls is a forest products 

technologist, U.S. Department of Agriculture, Forest Service, Pacific Northwest 

Research Station, Alaska Wood Utilization Research and Development Center, 

901C Halibut Point Road, Sitka, AK 99835; Maureen Puettmann is a consultant, 

WoodLife Environmental Consultants, LLC, 8200 NW Chaparral Dr., Corvallis, 

OR 97330; and Elaine Oneil is executive director, Consortium for Research on 

Renewable Industrial Materials, PO Box 352100, Seattle, WA 98195.
Abstract

Brackley, Allen M.; Nicholls, David L.; Puettmann, Maureen; Oneil, 

Elaine. 2017. Life cycle assessment of wood energy for residential heating—

opportunities for wood pellet production in southeast Alaska. Gen. Tech. Rep. 

PNW-GTR-951. Portland, OR: U.S. Department of Agriculture, Forest Service, 

Pacific Northwest Research Station. 34 p. 

Southeast Alaska is a remote area, located approximately 700 miles north of Seattle, 

Washington. Most of the region’s goods are imported by barge, creating logistical 

and economic challenges not faced by many other parts of the United States. In 

this context, we used life cycle assessment (LCA) to evaluate the potential environmental impact on global warming potential (GWP) of converting home heating 

systems from heating oil to wood pellets in southeast Alaska. Once the current level 

(status quo) was established, we evaluated imported pellet utilization at 20-, 40- and 

100-percent penetration into the residential heating oil markets. We also modeled 

local production of wood pellets in southeast Alaska, assuming a 20-percent penetration. Our research found that reductions in GWP resulting from the conversion 

to wood pellets ranged from 10 to 51 percent, with the greatest reductions being 

associated with the highest levels of imported pellets. The scenario of producing 

wood pellets in southeast Alaska to meet local needs had a reduction in GWP of

14 percent (versus the status quo).

Keywords: Pellets, wood energy, residential heating, global warming potential, 

water transportation.
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Life Cycle Assessment of Wood Energy for Residential Heating

Introduction

Climate change is an environmental issue of worldwide significance that has 

focused attention on the quantity of greenhouse gases released into the environment 

from the burning of fossil fuels. When planning wood-energy applications, it is 

critical to quantify the complete environmental impacts of harvesting, transporting, 

and combusting woody biomass for energy production, then compare these impacts 

to those of alternative fuel sources (often fossil fuels). Within this context, the conversion from fossil-fuel energy systems to biomass fuel sources is gaining momentum in southeast Alaska. Until recently, the increasing cost of petroleum-based 

heating fuel has biomass fuels such as wood pellets, wood chips, and firewood more 

cost-competitive, creating economic advantages for biomass. This is especially true 

in southeast Alaska, given the high cost of transportation to import heating oil into 

the region. Over the past 10 years, more than a dozen small-industrial-scale woodenergy systems have been installed in southeast Alaska. Although most of these 

systems are small (typically burning fewer than 100 cords of wood or 1,000 tons of 

chips per year), their cumulative impact motivated us to conduct life cycle assessment (LCA) research to quantify important decision variables as new wood-energy 

installations are brought online and new fuel-supply chains are established. To our 

knowledge, this research is the first to perform LCA on regionwide use of wood 

energy for residential heating that includes a substantial transportation component. 

Southeast Alaska is a rugged and sparsely populated island chain, rich in 

natural resources but isolated from the highway and rail systems that serve the 

mainland areas of North America. A limited industrial base makes it necessary 

to import almost all goods into the region, primarily by barge. In this report, we 

developed a baseline analysis that compares the environmental impact of heating oil 

versus wood pellets for residential heating. Total life cycle emissions result from the 

energy needed to collect, transport, process, and combust wood fuels. Accounting 

for these energy flows is critical to comparing alternatives in an LCA, such as the 

use of heating oil versus wood for residential heating. 

Life cycle assessment quantifies every stage in a product’s life and its interaction with the environment (fig. 1). The outcomes of an LCA can accurately target 

the source of environmental impacts throughout a product’s life. LCAs can be used 

to support development of more “environmentally friendly” products or sustainable 

production methods, and to provide insights regarding raw material conservation 

whether for wood energy or other products. Rigorous, quantitative LCAs can be 

valuable management tools to help formulate policies promoting environmental 

gains. Such assessments have evolved as an internationally accepted method to 
2

GENERAL TECHNICAL REPORT PNW-GTR-951

Figure 1—Life cycle of a biological material.

analyze complex impacts and outputs of a product or process and their environmental effects. As defined by the International Standards Organization (ISO 2006), an 

LCA is a multiphase process consisting of a life cycle inventory (LCI), life cycle 

impact assessment (LCIA), and life cycle interpretation. In this report, we used 

LCA to evaluate residential heating scenarios that included heating oil, cordwood, 

and wood pellets.

The LCI is an objective, data-based process of quantifying energy and raw 

material requirements, air emissions, waterborne effluents, solid waste, and other 

environmental releases occurring within the system boundaries. The LCIA process 

characterizes environmental releases identified in the LCI into impact categories 

such as global warming, acidification, carcinogenics, respiratory effects, eutrophication, ozone depletion, ecotoxicity, and smog. The tool for the reduction and 

assessment of chemical and other environmental impacts (TRACI) can be used to 

assess LCA environmental impacts, including those of pellet and heating oil production for the southeast Alaska model. This tool is a midpoint method developed 

by the U.S. Environmental Protection Agency (EPA) specifically for U.S. locations.
3

Life Cycle Assessment of Wood Energy for Residential Heating

Research Objectives

Our primary objective was to compare the environmental impacts of current levels 

of heating oil and cordwood use (the status quo) with the impact of using wood 

pellets as a replacement for fuel oil for residential heating in southeast Alaska. The 

emphasis of this analysis is the impact on the relative global warming potential 

(GWP) of these alternatives. Specifically, our research objectives were to develop a 

cradle-to-grave (extraction to combustion) LCA on the environmental impacts of:

(1) importing wood pellets into southeast Alaska from the Pacific Northwest, versus 

(2) local production of wood pellets in southeast Alaska to supplement current 

cordwood use. 

We compared heating oil, current cordwood use in southeast Alaska (the status 

quo), and the substitution of heating oil versus use of wood pellets. Additional 

assessments were performed on the availability of resources to sustain pellet 

production in southeast Alaska and meet local needs without importing pellets.

Residential Heating in Southeast Alaska

Southeast Alaska is characterized by remote communities, long transportation 

distances, high energy costs, and long heating seasons. Increased awareness among 

area residents of biomass energy and its potential cost savings has led to greater 

demand for heating products such as wood pellets, chips, and firewood. Wood 

energy has primarily been used in thermal applications (as opposed to electric power 

generation), and now includes several small-scale projects to heat governmental or 

institutional buildings, in addition to residential use. Several initiatives, including 

the southeast Alaska “bioenergy roadmap,” as well as funding initiatives to conduct 

feasibility studies, have provided support to potential wood-energy users.

Residential heating could soon benefit from forestry-related alliances in southeast Alaska. Viking Lumber Company (a wood products mill) and Sealaska Corporation (an Alaska Native corporation) have collaborated to promote regional biomass 

projects. As is commonly accepted, they have determined that the lowest cost wood 

feedstocks would come from lumber manufacturing residues. Aided by declining 

pulpwood markets, an estimated 25,000 green tons of wood residues would be available for wood pellet production regionally (Sealaska 2010). In addition to sawmill 

residues, higher cost woody feedstocks could be obtained from forest operations, 

including improved timber harvest log utilization and silvicultural treatments. 

Residential heating in southeast Alaska includes several fuel types (table 1). 

Heating oil represents the predominant use, with 64 percent of households,
4

GENERAL TECHNICAL REPORT PNW-GTR-951 Table 1—Current fuel use and household use for residential heating in southeast Alaska Fuel type

Community

Southeast Alaska 

households

Utility 

gas

LP 

gas Electricity

Heating 

oil Coal Wood

Solar 

energy Other None

Number

Percentage 

of total – – – – – – – – – – – – – – – – – Number of households – – – – – – – – – – – – – – – – –

Ketchikan 5,367 19.9 96 150 1,152 3,513 — 389 — 58 9

Wrangell 1,160 4.3 24 22 392 422 — 287 — 11 2

Petersburg 1,671 6.2 77 17 401 900 — 273 — 3 —

Sitka 3,623 13.5 37 159 1,058 2,121 5 209 — 25 9

Juneau 12,323 45.8 225 347 2,688 8,414 12 501 — 96 40

Hoonah 999 3.7 31 22 4 651 — 282 5 4 —

Haines 1,139 4.2 46 — 25 687 — 381 — — —

Skagway 395 1.5 17 23 8 313 — 30 — 4 —

Prince of Wales Island 250 0.9 — 13 4 108 — 121 — 4 —

Total 26,927 100 553 753 5,732 17,129 17 2,473 5 205 60

Percentage of total 2.1 2.8 21.3 63.6 0.06 9.2 0.02 0.76 0.22

LP = liquefied petroleum.Source: USDC CB (2012). 
5

Life Cycle Assessment of Wood Energy for Residential Heating

followed by electricity, wood, and gas (including liquefied petroleum (LP) (21, 9, 

and 5 percent of households, respectively) (USDC CB 2012). Southeast Alaska’s 

largest city, Juneau, contains 46 percent of the total households in southeast Alaska, 

and 68 percent of these are heated with heating oil. The largest percentage of wood 

use based on population is on Prince of Wales Island, where 48 percent of households use wood for home heating. Prince of Wales Island, however, has a relatively 

small population. Across southeast Alaska, households heating with heating oil 

outnumber those heated with biomass by nearly to 7:1 (table 2).

National and Regional Wood Pellet Production

In 2009, North America produced about 7 million tons of wood pellets, of which 

almost 5 million tons were exported to Europe (Pirraglia et al. 2010). In contrast, 

U.S. wood pellet producers supplied domestic markets with nearly 80 percent of 

their production. Wood pellet production in the lower 48 United States is centered 

near large sources of wood residue from primary wood products facilities. 

In southeast Alaska, forest products production infrastructure is generally 

lacking, allowing only small volumes of pellets to be produced economically. 

Currently, there is one small wood pellet manufacturer in southeast Alaska, 

producing about 800 tons annually. Expanded pellet production in the region will 

Table 2—Current energy use by household in southeast Alaska for heating oil and biomass

Community

Average annual 

energy use

Households in 

southeast Alaska

Number of households 

heating with fuel type

Percentage of households 

heating with fuel type

BTUs per 

household 

(× 106

) Number

Percentage 

of total Heating oil Biomass Heating oil Biomass

Ketchikan 71.56 5,367 19.9 3,513 389 20.5 15.7

Wrangell 77.07 1,160 4.3 422 287 2.5 11.6

Petersburg 77.07 1,671 6.2 900 273 5.3 11.0

Sitka 72.24 3,623 13.5 2,121 209 12.4 8.5

Juneau 85.75 12,323 45.8 8,414 501 49.1 20.3

Hoonah 86.44 999 3.7 651 282 3.8 11.4

Haines 86.44 1,139 4.2 687 381 4.0 15.4

Skagway 86.44 395 1.5 313 30 1.8 1.2

Prince of Wales Island 71.56 250 0.9 108 121 0.6 4.9

Total 714.60 26,927 100 17,129 2,473 100 100

BTUs = British thermal units.

Source: Brackley et al. (2010).
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GENERAL TECHNICAL REPORT PNW-GTR-951

require an expansion of the local forest products industry to supply waste residues 

from lumber manufacturing (including utility logs), combined with future opportunities to improve forests through thinning and other silvicultural practices. The 

possibility of establishing an economically viable local pellet mill is tenuous at best. 

Wood Pellet Market Potential for Southeast Alaska

An estimated 2,473 households in southeast Alaska currently use firewood for heating (Brackley et al. 2010). This demand translates to more than 17,000 tons of wood 

annually, assuming a wood moisture content of 14.5 percent and average woodstove 

efficiency of 75 percent. However, retail sales of wood pellets in Alaska have thus 

far met only a fraction of this demand. An estimated 32 retail stores in Alaska sold 

2,359 tons of bagged pellets in 2009 (Sealaska 2010). For wood pellets to penetrate 

even 20 percent of the heating oil market in southeast Alaska (3,426 households), 

a minimum of 22,000 tons of pellets annually would be required (based on pellet 

moisture content of 6.5 percent and average stove efficiency of 75 percent). Current 

regional pellet consumption is roughly 10 percent of this level.

As new wood-energy facilities become established in southeast Alaska, the 

type and form of wood fuel used will become an important determinant of delivered fuel cost, and in turn project economics. Some of the possible wood procurement strategies for southeast Alaska include: (1) using harvesting residues from 

forestry activities, (2) identifying firewood harvesting scenarios, or (3) importing 

wood pellets from the lower 48 states. As economies of scale become more fully 

developed, a wood pellet or other densified fuel facility could become established 

in southeast Alaska.

Prince of Wales Island, the largest land mass in the Alexander Archipelago 

(fig. 2), is the site of the largest sawmill in southeast Alaska, has extensive forest 

resources, and also has a well-developed road network. Our model considers Prince 

of Wales Island to be the region’s optimal location for pellet production, despite 

being located some distance from population centers such as Juneau and Sitka.

Because most markets in southeast Alaska can be served only by ship or air, 

many goods (including wood fuel) are more economical to import than to produce 

locally. This is likely to remain so until a wood-products infrastructure develops, 

one that is capable of processing the second-growth timber resources of the Tongass 

National Forest, in tandem with public acceptance of this harvest. The costs of 

importing pellets 700 miles from Seattle appear high unless they are compared with 

the high cost of producing goods within southeast Alaska, which in many cases can 

be even higher. 
7

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 2—Map of Prince of Wales Island communities and primary roads.
8

GENERAL TECHNICAL REPORT PNW-GTR-951

Background—Wood Pellet Production

Wood pellets are a renewable heating fuel produced from dried, compressed woody 

biomass, most commonly from primary and secondary wood manufacturing 

residues. Nearly 1 million U.S. homes use wood pellets for heat in free-standing 

stoves, fireplace inserts, furnaces, and boilers (Puettmann et al. 2015). Wood pellets 

are also used in larger scale applications such as schools, prisons, and government 

buildings. The Premium Grade Pellet Standard specifies a maximum inorganic 

ash content of 1 percent, a minimum specific gravity of 0.64 (40 pounds per cubic 

foot), and a maximum fines content of 0.5 percent by weight (PFI 2015). Standard 

Grade Pellets include the same criteria for fines, specific gravity, and dimensions 

but allow maximum ash content of 3 percent by weight. The energy content of 

wood pellets is approximately 8,000 to 8,500 BTUs per pound higher heating value 

depending on the composition of the wood and bark. Wood pellets are normally 

sold in 40-lb bags through local retailers.

Functional Units

Establishing the functional units is an important part of an LCA to allow for meaningful comparisons between different materials and alternatives. Functional units 

for residential fuel use in southeast Alaska are based on household annual energy 

requirements and higher heating values for each fuel used (cordwood, heating oil, 

or wood pellets) (table 3). 

System Boundary—Cordwood

The system boundary for cordwood involves individuals harvesting the wood for 

personal use. It is assumed that either standing trees are felled or downed timber 

is used. Our model assumed that all cordwood (firewood) was processed using 

chainsaws, then hand-hauled to personal vehicles for transport to households (fig 3). 

Table 3—Functional units for residential heating fuels used in southeast Alaska

Fuel type

Higher heating 

value Factor

Functional 

unit Units

Moisture 

content

Percent

Cordwood 7,398 0.75 5,549 BTUs per pound 14.5

Heating oil 139,000 0.78 108,000 BTUs per gallon —

Wood pellets 8,200 0.75 6,150 BTUs per pound 6.5

BTUs = British thermal units.
9

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 3—Cordwood life cycle assessment system boundary for residential heating in southeast 

Alaska.

System Boundary—Heating Oil

The system boundary for heating oil begins at extraction and ends with heating fuel 

combusted in residential oil heaters. We assumed that 100 percent of the heating oil 

was pumped from wells in Alaska, then delivered via pipeline to Valdez for loading 

onto ocean tankers, then shipped to the Seattle area for refining. The weighted average distance based on production used was 1,439 miles (2315 km). We assumed that 

heating oil would be shipped back to southeast Alaska (to the port of Ketchikan), 

reloaded onto smaller barges, and then transported to one of eight destination 

communities. The final step in this process would be truck delivery to individual 

households (often 15 miles or less).

System Boundary—Wood Pellet Production (Imported)

Two upstream feedstocks were used for the wood pellet production model; whole 

logs and sawmill residues (typically bark, slabs, edgings, and sawdust) (fig. 4). In 

the Pacific Northwest model, with pellet feedstocks originating from whole log 

chipping, the system boundary began with forest regeneration (Johnson et al. 2005) 

and ended with premium wood pellets. Upstream processes included planting seedlings, forest site preparation, fertilization, thinning, harvest, and log transportation 

for chipping to the pellet manufacturer (Johnson et al. 2005). For pellet feedstocks 

collected from sawmill residues, upstream processes for harvesting and lumber 

production and transportation of residues to the pellet mill are included. Pellet mill 
10

GENERAL TECHNICAL REPORT PNW-GTR-951

production includes unit processes for feedstock handling, size reduction, drying, 

screening, pelletizing, bagging, and pellet transport to the Port of Seattle (fig. 4). 

Our model assumed that pellets were transported by barge to the port of Ketchikan, 

then shipped by barge to one of eight destination communities, followed by road 

transport to retailers and finally end users. 

System Boundary—Wood Pellet Production (Local)

For premium wood pellets produced in southeast Alaska, we assumed that feedstocks would be obtained from either sawmill residues or whole logs (lower grade 

logs from sort yards or utility-grade logs from sawmills (fig. 5). In this model, the 

Figure 4—Life cycle assessment system boundary for imported wood-pellet production.
11

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 5—System boundary for southeast Alaska pellet production.

whole-log system boundary began with harvesting and ended with premium wood 

pellets. Pellet feedstocks collected from sawmill residues include the upstream 

processes of harvesting, lumber production, and transportation of residues to the 

pellet mill. All sawmill and whole-log chipping residues are considered to be green 

(i.e., undried). Our model assumed that pellet-mill production would include the 

following operations: feedstock handling, size reduction, drying, screening, pelletizing, bagging, and transportation to residential destinations (fig. 5). 
12

GENERAL TECHNICAL REPORT PNW-GTR-951

Methods

Once the status quo usage of heating oil and cordwood was established, our scenarios assumed that pellet manufacture occurred either in the Seattle, Washington, 

area or in southeast Alaska. Because current wood pellet use in southeast Alaska 

is assumed to be minimal, we simulated changes to the status quo at pellet usage 

levels of 20, 40, and 100 percent penetration using imported pellets (table 4). We 

also modeled 20-percent market penetration of the heating oil market for residential 

heating based on pellets produced in southeast Alaska. 

Residential heating was evaluated in nine communities: Haines, Hoonah, 

Juneau, Ketchikan, Petersburg, Prince of Wales Island, Sitka, Skagway, and 

Wrangell. Residential energy requirements are based on several interrelated variables, including quality of construction, amount and type of insulation, size of residence, average temperature, type of fuel used for heating, and type and efficiency 

of the heating system (Brackley et al. 2010). Our model is based on the average 

annual home heating requirements for each region as determined by the number of 

housing units for each community (table 5). 

Nearly half the households in southeast Alaska are located in Juneau (46 percent of total), while Prince of Wales Island has the fewest, spread over several 

communities (1 percent of total). The highest heating demands are for households 

Table 4—Life cycle assessment modeling scenarios for energy system 

comparisons

Scenario Cordwood use

Wood pellet 

usea Wood pellet source

Heating oil 

use

b

1 Current 

(status quo)

0 NA 100

2 Current 

(status quo)

20 Imported (from 

Pacific Northwest)

80

3 Current 

(status quo)

40 Imported (from 

Pacific Northwest)

60

4 Current 

(status quo)

100 Imported (from 

Pacific Northwest)

0

5 Current 

(status quo)

20 Locally produced 

(southeast Alaska)

80

NA = not applicable.

a

 As a percentage of non-cordwood energy use for residential heating.

b

 As a percentage of Scenario 1 heating oil use for residential heating.
13

Life Cycle Assessment of Wood Energy for Residential Heating

Table 5—Southeast Alaska cordwood use and energy consumption, by community 

Location

Total 

number of 

households

Number of 

households 

heating with 

cordwooda

Household 

cordwood use Energy use

Cordwood 

use

Cordwood 

use

Cordwood 

use

Percentage 

of total 

households

BTUs per 

household per 

year × 106 b

BTUs per 

location per 

year × 109 c

Tons per 

location per 

year

Average 

tons per 

household

Haines 1,139 381 33 86.44 32.94 2,986 7.84

Hoonah 999 282 28 86.44 24.38 2,210 7.84

Juneau 12,323 501 4 85.75 42.96 3,895 7.77

Ketchikan 5,367 389 7 71.56 27.84 2,524 6.49

Petersburg 1,671 273 16 77.07 21.04 1,908 6.99

Prince of 

Wales Island

250 121 48 71.56 8.66 785 6.49

Sitka 3,623 209 6 72.24 15.10 1,369 6.55

Skagway 395 30 8 86.44 2.59 235 7.84

Wrangell 1,160 287 25 77.07 22.12 2,006 6.99

Total 26,927 2,473 17,918 7.25

BTU = British thermal unit.

a B25040: House heating fuel—Universe: occupied housing units. 2008–2012 American community survey 5-year estimates. http://factfinder2.census.gov/faces/tableservices/jsf/pages/productview.xhtml?pid=ACS_12_5YR_B25040&prodType=table.

b Higher heating value ( HHV) = 8600 BTU/lb (0 percent MC); energy content of cordwood = 8,600–8,700 BTU/lb Alaska species.

c HHV = 7353 BTU/lb (14.5 percent MCw) (Ince 1979); woodstove efficiency = 75 percent; actual heat output = 5549 BTU/lb

(14.5 percent MCdb). 

 in the northern part of southeast Alaska, including Haines, Skagway, and Hoonah, 

requiring 86 million BTUs per household per year. The lowest household heating 

demand is on Prince of Wales Island and in Ketchikan, two southern locations, at 

71 million BTUs per household per year. Average residential energy consumption 

per household in southeast Alaska is estimated to be 79 million BTUs per household (Brackley et al. 2010). 

Southeast Alaska Cordwood Use

Residential use of cordwood (firewood) in southeast Alaska is still very limited and 

variable despite being abundantly available, and its source is often near communities. Regional use of cordwood for home heating ranged from 4 percent in Juneau to 

48 percent on Prince of Wales Island (with an average of 9 percent), based on number of households (USDC CBs 2014). Using energy consumption values and taking 

stove efficiency and wood moisture content into account, we estimate total annual 

firewood consumption in southeast Alaska to be more than 17,000 tons (table 5). 
14

GENERAL TECHNICAL REPORT PNW-GTR-951

Our models for cordwood extraction and use in southeast Alaska were based 

on surveys conducted in Wisconsin (Katers et al. 2012). The production processes 

were modified to reflect local (southeast Alaska) wood resources, access, and transportation distances. Collection of firewood in southeast Alaska assumed individual 

harvesting and transportation. Upstream processes regarding forest growth were 

also included. Natural regeneration was assumed because most harvesting scenarios 

would consider both standing and downedwood in old-growth forests. For individual harvest, we assumed that the only fuel consumption would be to operate 

chainsaws. Cordwood transportation was assumed to be done using personal 

vehicles with an average distance of 10 miles, for household consumption of 6.5 

to 7.8 tons annually (table 5).

Our model assumed three different residential wood stoves: (1) EPA-certified 

wood stoves with catalytic converters, (2) EPA-certified wood stoves without 

catalytic converters, and (3) uncertified conventional stoves.

Heating Oil Production

Heating oil is the primary energy source for residential heating in southeast Alaska, 

numbering more than 17,000 households (64 percent of all households in the region 

(USDC CB 2014)). However, there is great variation within southeast Alaska, with 

heating oil being used by less than 1 percent of households on Prince of Wales 

Island and 49 percent in Juneau (USDC CB 2014), based on number of households. 

Total heating oil consumption in southeast Alaska is estimated to be more than 11 

million gallons per year. 

The heating oil LCI data was obtained from the USLCI database (NREL 2012), 

in which heating oil represented 4.89 percent of the products produced. Therefore, 

4.89 percent of the burdens of all upstream processes (extraction and transportation) and the refinery process were assigned specifically to heating oil. Our model 

assumed that crude oil was shipped by oil tanker (ocean freighter) out of Valdez, 

Alaska, to refineries in Washington state. Because several ports exist in Washington, we used a weighted average based on production as a single mileage that was 

used in our model. 

Pellets Imported From Washington

Our LCA evaluated pellet production using both wet and dry mill residues from 

softwood lumber production in the Pacific Northwest. The Washington pellet model 

was based on pellet production surveys conducted in Wisconsin (Katers et al. 2012). 
15

Life Cycle Assessment of Wood Energy for Residential Heating

The production processes initially used in Wisconsin were modified to reflect wood 

resources, electricity generation, and transportation distances typical of western 

Washington. 

In our model, whole logs, wet mill residues, and dry mill residues were used 

to produce wood pellets in Washington. Final pellet furnish was derived from 

41-percent wet mill residues (dried by the pellet mill) and 59-percent dry residues 

(purchased from outside sources). The residues were comprised of common Pacific 

Northwest softwoods (Johnson et al. 2005), and mill residues were from local 

softwood lumber production (Milota et al. 2005). Our model assumed that softwood 

whole logs were obtained from Pacific Northwest thinning regimes (Johnson et al. 

2005), and chipped prior to drying. The SimaPro1 input/output process for transportation and processing whole-log feedstocks was used (Pré Consultants B.V. 2014)

(table 6). Our model also included wet and dry residues collected from softwood 

lumber mills (Milota et al. 2005) (table 7). All residue drying was by wood-fueled 

boilers, with wet wood residues dried to final moisture contents of between 12 and 

17 percent (oven-dry basis). 

Local Pellet Production

The forest resource in southeast Alaska, although abundant, is widely dispersed 

and is often located on steep slopes, thus is expensive to harvest and transport to 

manufacturing facilities as well as destination markets. Therefore, only high-value 

products can be produced economically. Because bioenergy products typically have 

low value, feedstocks must come to the manufacturing facility essentially free of 

charge, or they must be a waste product with an associated disposal cost, or the cost 

and market for the energy product must increase substantially in the future. These 

economic considerations dictated the system boundary for our LCA model and 

drove our assumptions for pellets manufactured in southeast Alaska as an alternative to heating oil. 

Low-grade materials suitable for use in energy products exist in all harvested 

areas, but economic considerations and the need for barge transportation make most 

of the material economically unrecoverable. In contrast, mill residues are typically 

available at lower costs. In southeast Alaska these residues would be mostly green 

and require drying. Because only limited wood-drying facilities exist in southeast 

Alaska, we structured our analysis to include wet residues at sawmills and log-yard 

residues that do not meet the specifications for export-grade logs as inputs to pellet 

manufacturing (table 8).

1

 The use of trade or firm names in this publication is for reader information and does not 

imply endorsement by the U.S. Department of Agriculture of any product or service.
16

GENERAL TECHNICAL REPORT PNW-GTR-951

Table 6—Unit process inputs/outputs for pellets produced in the Pacific Northwest and shipped to 

southeast Alaska (whole-log feedstocks)

Products Value in U.S. units Value in metric units

Handling and transporting whole trees (per short ton of feedstock):

Products

Wet chips from processed whole logs (90-percent allocation) 1.00 Tons 907.18 Kilograms

Bark for wood fuel (10-percent allocation) 222.23 Pounds 100.80 Kilograms

Materials/fuels:

Softwood logs with bark, harvested at average intensity site 78.75 Cubic feet 2.23 Cubic meters

Transport, single-unit truck, diesel powered 49.71 Ton-miles 72.58 Tonne-kilometers

Electricity/heat:

Electricity, at grid 17.11 Kilowatt-hours 17.11 Kilowatt-hours

Diesel, combusted in industrial equipment 0.49 Gallons 1.86 Liters

Natural gas, combusted in industrial equipment 0.01 Gallons 0.02 Liters

Handling and transporting wet mill residues (per short ton of feedstock):

Products:

Wet mill residues 1.00 Tons 907.18 Kilograms

Materials/fuels:

Pulp chips, softwood, green, at sawmill 1,000.00 Pounds 453.59 Kilograms

Sawdust, softwood, green, at sawmill 1,000.00 Pounds 453.59 Kilograms

Electricity/heat:

Diesel, combusted in industrial equipment 0.41 Gallons 1.54 Liters

Electricity, at grid 2.48 Kilowatt-hours 2.48 Kilowatt-hours

Natural gas, combusted in industrial equipment 0.01 Gallons 0.02 Liters

Transport, single-unit truck, diesel powered 79.54 Ton-miles 116.13 Tonne-kilometers

Handling and transportation of dry mill residues (per short ton of feedstock):

Products:

Dry mill residues 1.00 Tons 907.18 Kilograms

Materials/fuels:

Pulp chips, softwood, kiln dried, at planer 1,000.00 Pounds 453.59 Kilograms 

Planer shavings, softwood, kiln dried, at planer 1,000.00 Pounds 453.59 Kilograms

Transport, combination truck, diesel powered 49.71 Ton-miles 72.57 Tonne-kilometers
17

Life Cycle Assessment of Wood Energy for Residential Heating

Table 7—Unit process inputs/outputs for pellets produced in the Pacific Northwest and shipped to 

southeast Alaska (lumber mill residues)

Products Value in U.S. units Value in metric units

For pellet furnish in pellet production:

Products:

Pellet furnish 1 Tons 907.2 Kilograms

Materials/fuels:

Dry mill residues (dried onsite) 818.6 Pounds 371.3 Kilograms

Dry mill residues (purchased) 1,181.4 Pounds 453.6 Kilograms

Electricity/heat:

Electricity (at grid) 45.5 Kilowatt-hours 45.5 Kilowatt-hours

For drying wet mill residues:

Products:

Washington dry mill residues, at dryer 1 Tons 907.2 Kilograms

Materials/fuels:

Washington wet mill residues 1,000 Pounds 453.6 Kilograms

Washington wet chips from processed whole logs 1,000 Pounds 453.6 Kilograms

Electricity/heat:

Electricity, at grid 30.0 Kilowatt-hours 30.0 Kilowatt-hours

Wood fuel/wet feedstock/industrial boiler 3,036,629.2 BTUs 3,203.8 Megajoules

For palletization:

Products:

Wood pellets 1 Tons 907.2 Kilograms

Materials/fuels:

Pellet furnish 1 Tons 907.2 Kilograms

Low-density polyethylene resin, at plant 100.0 Pounds 45.4 Kilograms 

Transport, ocean freighter, residual fuel-oil powered 5,500.0 Ton-miles 8,029.9 Tonne-kilometers

Transport, combination truck, diesel powered 10.0 Ton-miles 14.6 Tonne-kilometers

Electricity/heat:

Electricity, at grid 100.3 Kilowatt-hours 100.3 Kilowatt-hours

Natural gas, combusted in industrial equipment 0.04 Gallons 0.14 Liters

Natural gas, combusted in industrial boiler 0.01 Gallons 0.03 Liters

Emissions to air:

Particulates 0.21 Pounds 0.09 Kilograms

Particulates, <10 μm 0.21 Pounds 0.09 Kilograms

Volatile organic compounds 1.00 Pounds 0.45 Kilograms

BTU = British thermal units.

The energy content of pellets = 8200 BTU/od lb (Katers et al. 2012).

Efficiency of pellet stove = 75 percent.

Source: Adapted from Katers et al. (2012).
18

GENERAL TECHNICAL REPORT PNW-GTR-951

Table 8—Unit process inputs/outputs for local pellet production in southeast Alaska

Products Value in U.S. units Value in metric units

Handling and transporting wet mill residues (per short ton of feedstock):

Wet sawmill residues (Craig, Alaska) 1 Tons 907.18 Kilograms

Materials/fuels:

Sawdust and chips, softwood, green, at sawmill (Craig, Alaska) 1481.5 Pounds 672 Kilograms

Electricity/heat:

Diesel, combusted in industrial equipment 0.07 Gallons 0.28 Liters

Electricity hydropower 0.45 Kilowatt-hours 0.45 Kilowatt-hours

Natural gas, combusted in industrial equipment 0.001 Gallons 0.004 Liters

Drying wet mill residues (per short ton of feedstock):

Dry pellet furnish (Craig, Alaska) 1.00 Tons 907.18 Kilograms 

Materials/fuels:

Wet sawmill residues (Craig, Alaska) 1347.99 Pounds 611.44 Kilograms 

Wet chips from processed whole logs (Craig, Alaska) 651.99 Pounds 295.74 Kilograms 

Electricity/heat:

Electricity (hydropower) 75.57 Kilowatt-hours 75.57 Kilowatt-hours

Wood fuel/wet feedstock/industrial boiler 3,036,629.21 BTUs 3,203.81 Megajoules

Adapted from Katers et al. (2012). 

Southeast Alaska Wood Products Residues as a 

Pellet Feedstock

The LCA model for production of wood pellets in southeast Alaska used 100-percent wet residues from softwood lumber production in Craig, Alaska (table 9). 

These residues were supplemented by whole pulpwood quality logs not suited for 

sawlogs or export. Our model, although based on Katers et al. 2012, was adjusted 

for local wood resource inputs, co-product allocation from sawmills, local electricity generation, and transportation. We assumed that one pellet mill located in the 

vicinity of Craig, Alaska would produce the pellets necessary for 20-percent substitution of the southeast Alaska heating oil residential market. Our model assumed 

that all residues would be chipped, screened, and dried in a horizontal drum dryer 

(table 8).

Wet mill residues represented 69 percent from softwood lumber production, 

with the remaining 31 percent coming directly from whole logs. Whole logs represented chipped utility logs (68 percent of total, based on scale) and recoverable 

residues (42 percent of total) at the export log yard. Lumber residues were a mix of 

sawdust and chips (51 percent of total), with lumber and bark comprising 39 and 9.4 
19

Life Cycle Assessment of Wood Energy for Residential Heating

Table 9—Local pellet production unit process inputs/outputs for pelletization, final step in

pellet production 

Products Value in U.S. units Value in metric units

Wood pellets, bagged (Craig, Alaska) 1.00 Tons 907.1847 Kilograms

Materials/fuels:

Pellet furnish (Craig, Alaska) 1.00 Tons 907.18 Kilograms

Low-density polyethylene resin, at plant 99.98 Pounds 45.35 Kilograms

Transport (ocean freighter, residual-fuel-oil powered) 16681.90 Ton-miles 26847.08 Tonne-kilometers

Electricity/heat:

Electricity (hydropower) 100.26 Kilowatt-hours 100.26 Kilowatt-hours

Natural gas (combusted in industrial equipment) 0.04 Gallons 0.14 Liters

Natural gas (combusted in industrial boiler) 0.01 Gallons 0.03 Liters

Emissions to air:

Particulates 0.21 Pounds 0.09 Kilograms

Particulates, <10 μm 0.21 Pounds 0.09 Kilograms

Volatile organic compounds 1.00 Pounds 0.45 Kilograms

Adapted from Katers et al. (2012).

percent, respectively. All residue drying was by wood fuel in boilers, over a moisture content range of 74 percent to 6.5 percent (oven-dry basis). Wet residue drying 

required close to 3 million BTUs per ton.

On Prince of Wales Island, at least 50,000 green tons of residuals are potentially 

available annually (TSS Consultants 2000). We report that 43,492 bone-dry tons per 

year are readily available on Prince of Wales Island, with a potential availability of 

up to 144,592 bone-dry tons per year. The results from this study indicate that at 

20-percent substitution of wood pellets, about 44,761 bone-dry tons per year would 

be required, while at 100-percent substitution, about 283,151 bone-dry tons per year 

would be needed.

Wood Pellet Production in Southeast Alaska

Wood pellets are manufactured when dry, fine particles are extruded through 

steel dies using machinery similar to that used for agricultural pellets. Final pellet 

dimensions are typically about 1⁄4 inch in diameter and 1 inch long. High pressures 

and temperatures soften lignin and bind the wood particles together to make uniform and consistent pellets. Although no adhesives are required, small amounts of 

lubricants and water can be added to improve pellet processing and formation. Hot 

pellets are stored in a hopper and allowed to cool before bagging, usually in small, 

semi-automated bagging lines. Filled bags of pellets typically weigh 40 lbs. 
20

GENERAL TECHNICAL REPORT PNW-GTR-951

Life Cycle Assessment Model Development

Our study included both an LCI and LCIA of pellet, heating oil, and cordwood 

production processes from cradle to grave. Life cycle inventories quantify emissions associated with all activities, from the resource extraction and fuel production through the use of fuels, including the transportation and distribution stages. 

Emissions released to the production of inputs were included based on their cradleto-grave activities. 

Our study followed the methods set forth in the ISO 14000 series of standards 

(ISO 2006). The LCA software used in our analysis was SimaPro version 8.03 

(PRé Consultants 2014). The LCIA phase establishes links between LCI results and 

potential environmental impacts and calculates impact indicators such as global 

warming potential, smog, eutrophication, and acidification (table 10). Environmental impacts are determined using the North American impact method, TRACI 

(Bare et al. 2011). Each impact indicator is a quantitative measure of one aspect of a 

potential impact, with indicators weighted equally.

We modelled wood pellet production using wet and dry mill residues from 

softwood lumber production in the Pacific Northwest and whole-tree chipping. The 

base model assumes that pellets are first produced in the Seattle, Washington, area, 

then are shipped by barge from the Port of Seattle to the Port of Ketchikan and 

other ultimate destinations, then by truck to a distribution center. Once pellets are 

delivered to each port, they are transported by truck for distribution and customer 

purchase. Our analysis was based on modelling assumptions for pellets, cordwood, 

and heating oil, which included specifying moisture content, heating values, and 

stove efficiencies (table 11).

Transportation flows for cordwood, heating oil, and imported pellets from 

extraction to combustion were determined, as well as distances transported both 

regionally (table 12) and locally (table 13). Our model assumed that locally produced pellets would be shipped by barge to Ketchikan (fig. 6), then distributed by 

the same means as imported pellets to each location in southeast Alaska. Pellets for 

residential use on Prince of Wales Island, when produced locally, would be transported by road to Hollis or Thorne Bay, Alaska, and loaded onto barges for shipment within southeast Alaska. Pellets shipped to Prince of Wales Island would be 

shipped by barge to Hollis or Thorne Bay and distributed by truck to retail outlets 

or households. 

It is known that tree growth, harvest, transportation, wood products manufacture, fuel production, and combustion result in carbon dioxide (CO2

) fluxes. This is 

often evaluated as GWP for a fixed time frame ranging between 20 and 500 years. 
21

Life Cycle Assessment of Wood Energy for Residential Heating

Table 10—Selected impact indicators, characterization models, and impact categories

Impact indicator Characterization model Impact category

Greenhouse gas emissions Calculate total emissions in the reference unit of CO2

equivalents for CO2, methane, and nitrous oxide.

Global warming

Releases to air decreasing or thinning 

of ozone layer

Calculate the total ozone forming chemicals in the stratosphere including CFCs, HCFCs, chlorine, and bromine. 

Ozone depletion values are measured in the reference 

units of CFC equivalents. 

Ozone depletion

Releases to air potentially resulting 

in acid rain (acidification)

Calculate total hydrogen ion (H+) equivalent for released 

sulfur oxides, nitrogen oxides, hydrochloric acid, and 

ammonia. Acidification value of H+ mole-eq. is used as 

a reference unit.

Acidification

Releases to air potentially resulting 

in smog

Calculate total substances that can be photo chemically 

oxidized. Smog-forming potential of O3 is used as a 

reference unit.

Photochemical smog

Releases to air potentially resulting 

in eutrophication of water bodies

Calculate total substances that contain available nitrogen 

or phosphorus. Eutrophication potential of N-eq. is used 

as a reference unit.

Eutrophication

Releases to air potentially resulting 

in respiratory effects

Calculate total carbon monoxide, nitrogen dioxide, 

nitrogen oxides, sulfur dioxides, ammonia, particulates 

<2.5 and <10 μm, and total suspended particulates

Respiratory effects

CO2 = carbon dioxide; CFC = chlorofluorocarbon; CHFC = hydrochlorofluorocarbon; O3 = ozone; N = nitrogen.

Table 11—Life Cycle Assessment modeling assumptions

Parameter Value

Premium wood pellet moisture content 6.5 percent (dry basis)

Cordwood moisture content 14.5 percent (dry basis)

Cordwood higher heating value 8,600a BTUs per pound 

Pellet higher heating value 8,200 BTUs per pound 

Heating oil higher heating value 140,000 BTUs per gallon 

Density of heating oil 7.2 pounds per gallon 

Cordwood stove efficiency 75 percent

Heating oil stove efficiency 78 percent

Pellet stove efficiency 75 percent

Alaska species mix density 672 kilograms per cubic meter 

(at 74-percent moisture content)

Carbon content of wood 50 percent

BTU = British thermal unit.

a

 This number was lowered from 8,653 BTUs per pound to an oven-dry moisture higher heating 

value of 8,600 BTUs per pound. Upon review of the SimaPro model (Pré Consultants B.V. 2014), it 

was discovered that cordwood was modeled using the lower higher heating value to calculate the fuel 

moisture content of 14.5 percent. Final use heating value was 7,353 BTUs per pound (Ince 1979).
22

GENERAL TECHNICAL REPORT PNW-GTR-951

Table 12—Distances used to model heating oil water transportation 

Port location Type of transport Distance

Miles Kilometers

Distance from port to port:

Valdez to Washington oil refinery Ocean freighter 1,439 2,316

Heating oil to Ketchikan Barge 751 1,209

Ketchikan Barge

Distance from Ketchikan, Alaska:

Wrangell Barge 103 166

Petersburg Barge 148 238

Sitka (inside passage) Barge 331 533

Juneau Barge 487 784

Hoonah Barge 465 748

Haines Barge 561 903

Skagway Barge 574 924

Prince of Wales Island Barge 39 63

Table 13—Southeast Alaska ground transportation distances modelled 

(heating oil and pellets)

Port location

Distance from port to 

distribution center

Distance from distribution 

center to residence

Miles Kilometers Miles Kilometers

Ketchikan 2.00 3.22 5.00 8.05

Wrangell 0.25 0.40 5.00 8.05

Petersburg 3.00 4.83 5.00 8.05

Sitka (inside passage) 5.00 8.05 5.00 8.05

Juneau 0.50 0.81 5.00 8.05

Hoonah 0.50 0.81 5.00 8.05

Haines 4.00 6.44 5.00 8.05

Skagway 0.25 0.40 5.00 8.05

Prince of Wales

Island (Thorne

Bay, Alaska)

10.00 19.09 5.00 8.05
23

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 6—Map of southeast Alaska region.
24

GENERAL TECHNICAL REPORT PNW-GTR-951

All calculations in this report for CO2 absorption during tree growth were based 

on well-established estimates of 50-percent carbon content for woody feedstocks 

(Milota et al. 2005). 

Net GWP is calculated by subtracting the CO2 absorbed during tree growth 

from the total CO2 emission (fossil- and biomass-based) occurring from cradle to 

grave. Global warming potential outputs were calculated using the TRACI version 

2.1 impact method within SimaPro software. Carbon dioxide absorption was calculated based on standing-tree resources to give a CO2 equivalent of standing volume 

or harvested volume. The TRACI impact method was modified to have CO2 from 

the combustion of biomass to be considered in the overall GWP.

Scenario 1: current use conditions (cordwood and heating oil)— 

Scenario 1 (base case) modeled heating oil and cordwood current use (status quo) 

for home heating in southeast Alaska, but did not consider the use of wood pellets 

(fig. 7). An estimated 2,473 households in southeast Alaska heat with cordwood

(9 percent of total) while an estimated 17,129 households (64 percent of total) heat 

with heating oil (Brackley et al. 2010). 

The carbon impact of residential heating in southeast Alaska is 204,357 tons 

CO2 eq. (table 14), with heating oil contributing 98 percent of this. Our analysis 

found that trees sequestered 30,075 tons of CO2 during growth, while cordwood 

Figure 7—Scenario 1: total global warming potential, carbon dioxide absorption, and net 

global warming potential for cordwood and heating oil in southeast Alaska.
25

Life Cycle Assessment of Wood Energy for Residential Heating

Table 14—Total global warming potential, carbon dioxide absorption, and net global 

warming potential for the five scenarios evaluated 

Scenario Fuel and level of use

Total global 

warming 

potential

Carbon 

dioxide 

absorption

Net global 

warming 

potential

Reduction 

from 

Scenario 1

- - - - - CO2 equivalent (metric tons) - - - - Percent

1 Cordwood 30,852 - 27,284 3,568

Heating oil, (100 percent) 181,939 -177 181,822

Total for southeast Alaska 212,791 -27,401 185,390

2 Cordwood 30,852 - 27,284 3,568

Heating oil (80 percent) 145,551 - 93 145,458

Imported pellets (20 percent) 62,668 - 45,203 17,465

Total for southeast Alaska 239,071 -72,580 166,491 10.2

3 Cordwood 30,852 - 27,284 3,568

Heating oil (60 percent) 109,163 -70 109,093

Imported pellets (40 percent) 125,337 - 90,554 34,783

Total for southeast Alaska 265,352 -117,908 147,444 20.5

4 Cordwood 30,852 - 27,284 3,568

Imported pellets (100 percent) 313,342 -226,014 87,328

Total for southeast Alaska 344,194 -253,298 90,896 51.0

5 Cordwood 30,852 - 27,284 3,568

Heating oil (80 percent) 145,551 - 93 145,458

Local pellets (20 percent) 56,827 - 46,481 10,346

Total for southeast Alaska 233,230 -73,858 159,372 14.0

combustion released 34,008 tons CO2 eq., resulting in a net GWP of 2 percent. 

For Scenario 1, net GWP for cordwood was 3,933 tons CO2 eq., while for heating 

oil the net GWP exceeded the total GWP for cordwood at 200,424 tons CO2 eq. 

(table 14). Unit process inputs and outputs for cordwood were modelled for collection (table 15) and for combustion (table 16).

Scenario 2: Cordwood status quo, heating oil (80 percent), imported pellets 

(20 percent)— 

In Scenario 2, residential cordwood use remained constant, while 20 percent of 

household energy from heating oil was substituted with the equivalent energy in 

wood pellets. The pellet production for Scenario 2 originated from a hypothetical 
26

GENERAL TECHNICAL REPORT PNW-GTR-951

Table 15—Unit process inputs and outputs for modelling cordwood collection 

in southeast Alaska

Products Value Unit Value Unit

Cordwood for residential heating in 

southeast Alaskaa 1.00 Tons 907.18 Kilograms

Materials:

Cordwood harvested in southeast 

Alaska

74.85 Cubic 

feet

2.12 Cubic meters

Gasoline, combusted in equipmentb 0.08 Gallons 0.31 Liters

Lubricants 0.0107 Pounds 0.0049 Kilograms

a

 Density of southeast Alaska cordwood = 428 kg/m3. Based on oven-dry specific gravity for Sitka spruce (25 

percent of total), western hemlock (50 percent of total), and red alder (25 percent of total) (USDA FS 2010). 

b

 National average for chainsawing operations used for thinning operations (Johnson et al. 2005, 

Oneil et al. 2009). 

Table 16—Unit process inputs/outputs for cordwood combustion in wood 

burning stoves in southeast Alaska

Products Value Unit

Heat from cordwood (average Alaska stove)/ 1.00 Megajoules

Materials/fuels:

Heat from cordwood (EPA-certified catalytic heaters) 0.219 Megajoules 

Heat from cordwood (EPA-certified non-catalytic heaters) 0.206 Megajoules 

Heat from cordwood (uncertified conventional heaters) 0.575 Megajoules 

pellet plant located in the vicinity of Seattle, Washington. Twenty percent of the 

energy market of heating oil represented 275 billion BTUs for southeast Alaska, 

the equivalent of 22,414 tons of wood at 6.5 percent moisture content, and an assumed stove efficiency of 75 percent. This scenario allocated 3,426 out of 14,129 

households currently heating with heating oil. Table 14 shows the total GWP, CO2

absorption, and net GWP for Scenario 2. 

Carbon released from woody biomass combustion is considered to be neutral 

because it is removed from the atmosphere by trees during growth) (Beauchemin 

and Tampier 2008). The total GWP for southeast Alaska under this scenario was 

183,524 tons CO2 eq. a 10.2-percent decrease versus the base case (table 14).

Scenario 3: Cordwood, heating oil (60 percent), imported pellets (40 percent)— 

This scenario doubles the use of pellets (from 20 to 40 percent), thereby doubling 

the GWP impact for pellets (fig. 8). However, under Scenario 3, the net southeast 
27

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 8—Scenario 3: total global warming potential, carbon dioxide absorption, and net global 

warming potential for cordwood, 60-percent heating oil, and 40-percent imported pellet use in 

southeast Alaska.

Alaska GWP was lowered by 20.5 percent relative to scenario 1 (table 14). When 

wood pellets made up 40 percent of the heating-oil energy use, total GWP for pellets was slightly above that for heating oil (120,332 tons CO2 eq. for heating oil and 

138,160 tons CO2 eq. for pellets). Similarly to the results from scenarios 1 and 2, 

under scenario 3 the number of households using wood is driving the differences in 

GWP, not the emissions from pellet transportation. Because energy and resources 

are consumed to make energy, there are primary fuels and resources consumed during extraction, production, and transportation. 

Scenario 4: Cordwood, imported pellets (100 percent)— 

In scenario 4, cordwood use remained constant and heating oil was not used at

all (i.e., 100 percent of this energy demand was met by imported wood pellets) 

(fig. 9). This scenario produces a net carbon benefit by reducing net GWP in southeast Alaska by 51 percent from the base case (Scenario 1) (table 14). Given the 

existing forest resource economy and resource availability for pellet production in 

southeast Alaska, Scenario 4 is only possible using imported wood pellets. As such, 

Scenario 4 would still require a significant amount of fossil-fuel energy to transport 
28

GENERAL TECHNICAL REPORT PNW-GTR-951

Figure 9—Scenario 4: total global warming potential, carbon dioxide absorption, and net global 

warming potential for cordwood and 100-percent imported pellet use in southeast Alaska. 

pellets to each port and distribution center in southeast Alaska. Total primary fossilfuel energy consumption decreased 38 percent from the base case (Scenario 1), 

while total primary fuels only decreased by 16 percent, with 23 percent of the total 

energy coming from biomass used to process the pellets. 

Scenario 5: Cordwood, heating oil (80 percent), local pellets (20 percent)— 

Scenario 5 is the only Scenario that considered pellet production in southeast 

Alaska. Here, we assumed that pellets would be produced on Prince of Wales Island 

near the lumber mill in the vicinity of Klawock, Alaska. The primary distinction 

between Scenarios 5 and 2 is the need in Scenario 5 for pellet transportation from 

Seattle, Washington, to Ketchikan, Alaska. The removal of this transportation component, combined with the use of only wet mill residues, lowered the GWP under 

Scenario 5 from 183,528 tons of CO2 eq. per year to 175,678 tons. Thus, a reduction of 14 percent in GWP was realized by replacing only 20 percent of the heating oil use with local pellet production (table 14). Locally produced pellets reduced 

GWP only 4 percent compared to imported pellets under the same usage level (i.e., 

equivalent to 20 percent of the heating oil use) (fig. 10). 
29

Life Cycle Assessment of Wood Energy for Residential Heating

Figure 10—Scenario 5: total global warming potential, carbon dioxide absorption, and net global 

warming potential for cordwood, 80-percent heating oil, and 20-percent local pellet use in southeast 

Alaska.

Results and Discussion

The infrastructure needed to establish pellet markets in southeast Alaska will likely 

be the largest hurdle in establishing a self-sustaining pellet industry within the 

region. In this context, infrastructure needs would include harvesting equipment, 

transportation and trucking equipment, wood products mills, and wood drying 

facilities at a minimum. Outside of Prince of Wales Island, there is a reduced log 

supply, and there are few mills producing residuals. In addition, there are few 

commercial dry kilns in southeast Alaska, or secondary manufacturing facilities, 

meaning that all pellet feedstock residues would need to be dried (requiring additional energy inputs). 

There are also other practical barriers. Rainy weather conditions in southeast 

Alaska make it difficult to maintain low pellet moisture contents unless they are 

stored in closed containers or bagged. Further, bulk handling systems are often 

difficult to use, especially for smaller producers just entering this industry. As an 

alternative, interest is growing in producing larger “wood energy bricks” (typically 

up to 4 inches maximum dimension) instead of pellets. These “bricks” have the dual 
30

GENERAL TECHNICAL REPORT PNW-GTR-951

advantage of being able to replace firewood in conventional stoves while having 

greater weather resistance than pellets. At least one firm on Prince of Wales Island 

is actively producing wood energy “bricks.”

Although many locations in the continental United States have a wellestablished network of roads and wood products facilities, this is not the case in 

southeast Alaska. Here, there is only one medium-size sawmill (on Prince of Wales 

Island). Further, most markets can be served only by barge or air owing to the 

isolated nature of island communities and the lack of a road system to connects 

them. All these challenges point to the reality that many of southeast Alaska’s 

goods (including wood fuel) are often more economically shipped in from outside 

locations than produced locally. 

Comparing GWP per energy unit for complete substitution of heating oil in 

southeast Alaska with wood pellets, a reduction in net GWP of 14.0 percent could 

be achieved if pellets were to be produced locally and a 10.2-percent reduction in 

net GWP would be seen if the same level of imported pellets were used (table 14). 

Substitution levels at 20-percent heating oil resulted in the greatest reduction in 

both GWP and energy use when compared to the current scenario of 100-percent 

heating oil and no pellets. The cradle-to-grave fuel production and use impacts at 

the 20-percent substitution level produced only modest differences in GWP between 

locally and imported pellets because of the remaining high use of heating oil. 

When considering differences in individual fuel production and use, our main 

interest was in the overall impact on southeast Alaska as a whole, based on different levels of pellet use and total energy use. Energy reductions can be associated 

with less transportation of both heating oil and pellets, and less energy required for 

pellet production. As noted previously, locally produced pellets use only wet mill 

feedstocks, which are dried once they are processed into pellet furnish. Because the 

imported pellets used feedstocks from dried mill residues, a portion of the upstream 

embodied energy was allocated for drying. The shipping distances for heating oil 

(assumed to originate in Alaska) were nearly double that of imported wood pellets 

in our analysis. Because Prince of Wales Island and Skagway had the fewest households using heating oil, transportation scored highest in almost all of the impact 

categories. We found that for both pellets and heating oil fuel, unless fuel consumption is substantial, transportation will be the main GWP contributor. The GWP 

was highest for combined extraction, production, and use for every location except 

Prince of Wales Island and Skagway. Similarly to the scenario of 20-percent pellet 

use, the extraction, production, and use stages showed higher impact contributions 

in all nine impact categories for southeast Alaska’s largest communities (Juneau, 

Sitka, and Ketchikan). In most locations the difference in GWP between extraction, 
31

Life Cycle Assessment of Wood Energy for Residential Heating

production, use and transportation was significant (accounting for up to 96 percent 

of total impact). However for smaller communities such as Wrangell and Skagway, 

this was not the case (accounting for 5 percent or less of total impact). 

When we considered the GWP of residential heating fuels, total household fuel 

usage played a much greater role in GWP than did transportation. For example, 

for households using either heating oil or imported pellets, Juneau had the highest 

numbers, with 8,414 and 1,683 households heating with heating oil and pellets, 

respectively. Prince of Wales Island, with the lowest population of any location in 

our model, had only 108 households heating with heating oil and 22 households 

heating with pellets. 

Summary

Wood pellet use for residential heating in southeast Alaska was evaluated using 

modelling techniques as a cradle-to-grave LCA. This analysis allowed comparing 

of the GWP of imported wood pellets, locally produced pellets, locally produced 

cordwood, and heating oil. Substitution of heating oil with pellets was assessed at 

the 20-, 40-, and 100-percent levels. Cordwood use remained the same for all comparisons (i.e., the status quo). Global warming potential (kg CO2 eq.) was lower for 

all substitution scenarios versus the current case that assumed 100-percent heating 

oil plus cordwood use. 

Several assumptions were made in this study owing to the lack of actual pellet 

production data in southeast Alaska and Washington State. The results do strongly 

indicate the environmental advantage of increase use of wood-based biofuels in 

southeast Alaska for residential heating. Environmental benefits can be further 

enhanced when fuel is produced locally to alleviate the transportation burdens 

associated with importing goods to southeast Alaska. Although we focused primarily on carbon impacts, there are several other environmental impacts that could be 

reported when investigating fuel substitutions, such as smog, respiratory effects, 

and ozone depletion. 

Forest resource use is a continually evolving issue in southeast Alaska, and 

estimating future timber harvest and the availability of material suitable for energy 

use in southeast Alaska has large uncertainties. The Tongass National Forest transition to young growth is underway, and, over the next few decades, this resource, 

and its ability to generate wood-energy feedstocks in the form of harvesting residues, small-diameter timber, and sawmill residues, will have a major impact on the 

region’s ability to locally produce forest products. 
32

GENERAL TECHNICAL REPORT PNW-GTR-951

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 25.4 Millimeters (mm)

Feet (ft) 0.3048 Meters (m)

Miles (mi) 1.609 Kilometers (km)

Pounds (lb) 0.4536 Kilograms (kg)

Tons (ton) 0.907 Tonnes

Degrees Fahrenheit (°F) 56(°F – 32) Degrees Celsius (°C)

British thermal units (BTU) 0.00106 Megajoules (MJ)

Pounds per square inch (psi) 0.006895 Megapascals (MPa)

References

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