United States 

Department of 

Agriculture

Forest Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-783

January 2009

Cordwood Energy Systems for 

Community Heating in Alaska–

An Overview

David Nicholls and Tom Miles

DEPAR TMENT OF AGRICULT URE
The Forest Service of the U.S. Department of Agriculture is dedicated to the principle of 

multiple use management of the Nation’s forest resources for sustained yields of wood, 

water, forage, wildlife, and recreation. Through forestry research, cooperation with the 

States and private forest owners, and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide increasingly greater service 

to a growing Nation.

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, disability, and where applicable, 

sex, marital status, familial status, parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all or part of an individual’s income 

is derived from any public assistance program. (Not all prohibited bases apply to all 

programs.) Persons with disabilities who require alternative means for communication of 

program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination, write 

USDA, Director, Office of Civil Rights, 1400 Independence Avenue, SW, Washington, DC 

20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal 

opportunity provider and employer.

Authors 

David Nicholls is a forest products technologist, U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station, Alaska Wood Utilization 

Research and Development Center, 204 Siginaka Way, Sitka, AK 99835; and 

Tom Miles is a consultant, T.R. Miles, Technical Consultants, Inc., 1470 SW 

Woodward Way, Portland, OR 97225.

Cover photos: top and bottom left by David Nicholls. Bottom right by Daniel Parrent.
Abstract

Nicholls, David; Miles, Tom. 2009. Cordwood energy systems for community 

heating in Alaska—an overview. Gen. Tech. Rep. PNW-GTR-783. Portland, OR: 

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

Station. 17 p. 

Wood has become an important energy alternative in Alaska, particularly in rural 

areas where liquid fuel costs can be substantial. In some cases, wood fuel is readily available to communities, increasing the attractiveness of wood energy. Wood 

energy systems in rural Alaska can also lead to employment gains as well as 

benefits to local cash economies. Many Alaska villages are now considering wood 

as a fuel source for community heating, several have completed feasibility studies, 

and others are moving forward with design and construction activities.

Cordwood is readily available in many regions of Alaska, although not always 

in commercial quantities. However, for many small-scale applications, efficient 

cordwood systems could be a viable energy option. In this paper, we provide a 

qualitative review of factors such as wood fuel availability, cordwood system size, 

wood fuel cost, wood quality, labor, fuel drying, and underground piping. Other 

general observations are noted, based on case studies of operating cordwood 

systems in Alaska.

Keywords: Wood energy, cordwood, rural Alaska, community development, 

economic development.

Cordwood Energy Systems for Community Heating in Alaska—An Overview

Introduction

Woody biomass has become an increasingly important energy alternative as fossil 

fuel prices have risen in recent years. This is particularly apparent in rural Alaska, 

where many communities depend on fuel oil for their primary energy needs. In 

some cases, fuel must be flown in to remote communities at considerable expense, 

resulting in delivered heating oil costs greater than $6.00 per gallon based on 

September 2006 prices (table 1). When relatively inexpensive wood energy systems 

can be used to burn wood in place of high-priced heating oil, the result can often 

be major cost savings. Low-cost cordwood, generated from forest residues, hazard 

fuel removals, or sawmill residues, can further increase the attractiveness of wood 

energy systems. An added benefit of rural wood energy systems may be increased 

local employment needed for fuelwood harvesting, transportation, and system 

operation. In some areas of Alaska, regional production and delivery of cordwood 

serving numerous communities might be possible (while also resulting 

in economies of scale needed for business startups).

A recent review of potential wood energy sites in Alaska has revealed generally 

strong potential for thermal systems providing heat for schools and other community buildings (Miles 2006). This report also determined that for many applications over a given range of system sizes, high-efficiency cordwood systems could 

be economically attractive. More expensive chip-fired systems, having automated 

fuel loading and other automated features, would be cost effective only for larger 

systems (i.e., those displacing more than about 100,000 gal of heating oil per year). 

Many of the community heating applications in Alaska villages would be best 

suited for cordwood systems, but would not be large enough to justify the expense 

of automated chip-fired systems.

This paper considers the feasibility of efficient cordwood energy systems for 

community heating in rural Alaska. These systems are characterized by efficient 

wood combustion and energy transfer to water, typically held in a jacket surrounding the combustion chamber. Efficient systems often have firebrick or other 

refractory material lining the combustion chamber, resulting in higher burning 

temperatures and more complete combustion. Efficient, controlled combustion 

conditions lead to low particulate emissions and generally good air quality. 

We provide a qualitative review of factors such as wood fuel availability, 

cordwood system size, wood fuel cost, wood quality, labor, fuel drying, and air 

quality. Other general observations are noted, based on case studies of cordwood 

systems in Alaska. It is not within the scope of this paper to provide a detailed 

economic analysis nor an evaluation of engineering or design parameters. However, 

these items would become important for wood energy sites having strong potential 

A recent review of 

potential wood energy 

sites in Alaska has 

revealed generally 

strong potential for 

thermal systems 

providing heat for 

schools and other 

community buildings.
GENERAL TECHNICAL REPORT PNW-GTR-783 

for development, and would be conducted after preliminary feasibility studies. 

For the purposes of this paper, we use the term “cordwood” to refer to all forms 

of solid wood biomass that has not been reduced to chips or other small pieces. 

Therefore, “cordwood” will also encompass firewood, roundwood, stickwood, 

slabs, and edgings.

Table 1—Delivered heating oil costsa in Alaska communities

Transport

Fuel oil method for

Alaska community Region No. 1 cost fuel delivery Primary fuel use

Dollars

per gallon

Alatna Interior 4.50 Air Home heating

Arctic Village Interior 6.36 Air Electrical generation and heating

Eagle Interior 3.00 Truck Home heating

Hughes Interior 6.00 Air Public facilities and heating

Tanana Interior 4.69 Barge, air Home heating

Regional average (interior) 4.91

Kaktovik North slope 1.75 Barge Hunting

Nuiqsut North slope 2.25 Truck Electricity generation

Regional average (north slope) 2.00

Chignik South coastal 3.45 Barge Home heating

King Cove South coastal 3.08 Barge Public

Larsen Bay South coastal 3.22 Barge All

New Stuyahok South coastal 4.87 Barge Public

Saint George South coastal 4.47 Barge Public use vehicles

Togiak South coastal 4.07 Barge Home heating

Valdez South coastal 2.97 Barge, truck Home heating

Regional average (south coastal) 3.73

Gustavus Southeast 3.08 Barge Electrical generation and heating

Kake Southeast 3.70 Barge Home heating

Point Baker Southeast 4.10 Barge Electric generation

Wrangell Southeast 3.47 Barge Home heating, electrical generation

Regional average (southeast) 3.59

Atmautluak Western 3.92 Barge No response

Deering Western 3.80 Barge No response

Golovin Western 4.42 Barge Multipurpose

Kotlik Western 4.41 Barge Heating fuel, outboard motors

McGrath Western 4.87 Barge Sales to public

Grayling Western 5.60 Barge Transportation and facilities

Russian Mission Western 5.32 Barge Home heating

Shishmaref Western 2.99 Barge Home heating

Teller Western 4.79 Barge Home heating

Tuntutuliak Western 4.27 Barge Home heating

White Mountain Western 3.69 Barge Home heating, subsistence

Regional average (western) 4.37

a Delivered cost of No. 1 fuel oil, current as of September 2006, as indicated by survey response.

Source: State of Alaska 2006.
Cordwood Energy Systems for Community Heating in Alaska—An Overview

Small-Scale Wood Fuel Heating Systems

Cordwood Systems

Cordwood systems are generally appropriate for smaller applications where the 

maximum heating demand ranges from 100,000 to 900,000 British thermal units 

(BTUs) per hour (Miles 2006). Cordwood or sawmill residues are manually loaded 

into the boiler (i.e., they are “stoked”), often several times per day. An important 

consideration for cordwood systems is the ability to find dependable and costeffective labor to stoke the system when needed, and to perform minor maintenance 

and repair.

Cordwood systems can further be divided into high-efficiency systems (in 

which controlled combustion is used to minimize particulate emissions) and lower 

efficiency systems (in which burning conditions are less controlled and air quality 

is generally reduced). Cordwood systems generally represent a “low technology” 

wood energy option, and small systems often cost less than $100,000. Energy 

systems displacing between 2,500 and 30,000 gal per year would be suitable for 

cordwood (Parrent 2007).

Bulk Fuelwood Systems

Bulk fuelwood systems that burn chips, sawdust, bark, hog fuel, and shavings 

among other fuel types are generally found where the maximum heating demand 

exceeds 1 million BTUs per hour. Owing to the need for automated systems to 

store and convey wood, the cost of bulk fuel systems is often multiples of that of 

cordwood systems. It is not uncommon for complete systems to cost in excess of $1 

million. A key advantage of these systems is that little or no labor is needed for fuel 

handling, a significant cost savings over the life of a wood energy system.

For Alaska communities considering bulk fuelwood systems, important factors to consider are the system size (i.e., the displaced volume of fuel oil) and the 

ability to secure a dependable and economical source of bulk fuel. Often, this bulk 

fuel could be hog fuel or other sawmill residues, or chipped residues from salvage 

operations (e.g., beetle-killed or fire-killed trees). An important consideration for 

bulk fuel systems is that wood chips are often generated as part of larger production facilities (e.g., medium and large sawmills, biomass export facilities, etc.) and 

therefore would not be well suited to the scale needed for many of the bioenergy 

applications in rural Alaska. Regardless of which wood energy design is used, an 

existing oil-fired system could be retained for backup use during wood energy 

system downtime. 

An important 

consideration for 

cordwood systems 

is the ability to find 

dependable and 

cost-effective labor 

to stoke the system 

when needed, and 

to perform minor 

maintenance and 

repair.
GENERAL TECHNICAL REPORT PNW-GTR-783 

High-Efficiency Cordwood Energy Systems

High-efficiency cordwood energy systems are designed to burn cordwood fuel 

cleanly with a minimum of particulate emissions. A significant difference between 

high- and low-efficiency cordwood systems is that high-efficiency systems make 

better use of fans to control combustion conditions, and typically have larger water 

storage units resulting in more efficient heat transfer to the end destination. Highefficiency systems also typically have refractory firebrick lining the firebox, helping 

to maintain high temperatures in the combustion chamber.

Several high-efficiency systems are in use in Alaska. A Tarm1 gasification 

boiler is being used to heat a house in Palmer, Alaska. Tarm USA supplies boilers 

from 100,000 to 198,000 BTUs per hour maximum heat output and claims heating 

efficiencies of 80 percent (Tarm USA Inc. 2003). 

A GARN burner by Dectra Corporation is used in Dot Lake, Alaska, to heat 

several homes and a laundromat, replacing 7,000 gal per year of No. 2 fuel oil 

(Dectra Corporation 2008). This system has a heat output of 900,000 BTUs per 

hour, and uses 4,400 gal of water to heat seven homes and the laundry facility 

(Frederick 2007). High-efficiency cordwood burners are ideal for applications from 

100,000 to 1 million BTUs per hour, although both larger and smaller applications 

are possible (Parrent 2008). 

Table 2 shows the results for a GARN cordwood energy system tested between 

157,000 and 173,000 BTUs per hour by the state of Michigan, and using the new 

American Society for Testing and Materials testing procedures (with comparison 

to U.S. Environmental Protection Agency standards for wood stoves and boilers). 

At 0.00631 oz per million BTUs, the GARN system had the lowest particulate 

emissions of any of the systems tested. It is important to remember that wood-fired 

systems are not entirely smokeless, and even very efficient systems can burn less 

cleanly for several minutes during startup (Intertek 2006, Miles 2006). 

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.

Table 2—Particulate emissions from wood heating systems

Systems Particulate emissions

Ounces per million BTUs

EPA certified noncatalytic stove 0.0176

EPA certified catalytic stove .0088

EPA industrial boiler .0079

GARN WHS 1350 boiler .0063

EPA = U.S. Department of the Interior, Environmental Protection Agency.

Source: Intertek Testing Services 2006.
Cordwood Energy Systems for Community Heating in Alaska—An Overview



Some general features of high-efficiency cordwood burners include the 

following:

• Manually fed 

• Relatively high boiler efficiencies (70 percent or higher)

• Typical heat output into storage of 350,000 to 950,000 BTUs per hour 

• Controlled combustion conditions—generally good air quality with low 

levels of particulate emissions 

• Many have water storage capacities ranging from about 1,500 to 4,400 gal

Practical Considerations for High-Efficiency 

Cordwood Energy Systems

System Cost

High-efficiency cordwood systems are a relatively inexpensive wood energy option 

owing, in part, to their simple design, higher labor requirements, and lack of 

automation (vs. more expensive chip-fired systems). Small cordwood systems are 

often available for less than $100,000, even in Alaska where construction, transportation, and labor are all likely to be more expensive than locations in the continental 

United States.

For example, the estimated costs of equipment for two separate cordwood 

systems are $37,000 (Craig, Alaska) and $31,900 (Thorne Bay, Alaska) (Miles 

2006). Each of these systems is rated at 350,000 BTUs per hour. A somewhat larger 

system (rated at 450,000 BTUs per hour), requiring a larger boiler and more piping, 

had an estimated cost of $104,300. An important variable influencing project cost 

is the potential need to construct new buildings (or renovate existing buildings) to 

house the wood energy system and fuel storage. Low-cost construction (e.g., pole 

barns) can be used in some cases. In other cases, cordwood energy systems could 

be installed in existing buildings.

Given the potential for significant cost advantages in favor of high-efficiency 

cordwood systems, they should not be overlooked as a viable option for wood 

heating in rural Alaska where either roundwood or sawmill residues are available, 

and where system requirements of less than about 1 million BTUs per hour are 

expected.

Wood Fuel Source

Many Alaska communities are close to forested areas that in some cases (notably in 

interior Alaska) are not capable of producing commercial sawtimber, but could produce abundant small-diameter cordwood. Community heating needs can often be 

met sustainably by harvesting cordwood that is close to communities, in relatively 

Given the potential 

for significant cost 

advantages in favor 

of high-efficiency 

cordwood systems, 

they should not 

be overlooked as 

a viable option for 

wood heating in 

rural Alaska.
GENERAL TECHNICAL REPORT PNW-GTR-783 

small amounts on a sustainable basis. For example, a proposed wood energy system 

in McGrath, Alaska, would require harvesting only 20 to 30 ac (250 cords) annually 

(McGrath Light and Power 1999). In some cases, fuel sources are close enough to 

a community to be considered a hazard, with increased urgency of removal (these 

areas are commonly called wildland-urban interface zones).

In other cases, communities plan to sustainably harvest biomass as part of longterm forest management plans. In the Fort Yukon area of interior Alaska (fig. 1), it 

is estimated that 15,000 tons of biomass per year could be harvested on 833 ac/yr 

to meet regional village heating and electrical needs (Olsen 2007). This evaluation 

assumed a biomass yield of 18 tons/ac and a rotation age of 60 years, with approximately 50,000 ac of forest land being managed. In many interior Alaska communities, there are no sawmills or existing forest products infrastructure that produce 

wood residues. Therefore, sustainable harvests for wood energy could represent a 

high-value use of forest resources.

Figure 1—Alaska, by geographic region (source: State of Alaska 2008).
Cordwood Energy Systems for Community Heating in Alaska—An Overview

For communities close to sawmills, lumber slabs and 

edgings (fig. 2) could potentially be combined with cordwood 

and burned in efficient cordwood systems. When sawmill 

residues are available inexpensively, significant economic 

benefits can result vs. the use of harvesting residues or other 

more expensive biomass. Some Alaska sawmills are known 

to have excess sawmill residues that would likely be available 

at little or no cost for wood energy systems; however, some 

transportation costs would usually be required.

Air-Drying of Fuelwood

The recoverable energy from cordwood is increased by drying 

before burning, in order to realize greater heating values. A 

rule of thumb is to dry wood to about 20 percent moisture content (green basis) 

before burning. In some cases, little or no air drying would be needed; for example, 

when using fire-killed spruce (Picea spp.) trees (Frederick 2008). Initial moisture 

content, air-drying temperature and humidity, wood density, diameter, and the presence of bark are all variables that can influence air-drying times. 

In certain regions of Alaska (notably interior Alaska), air drying could occur 

relatively quickly during summer periods of low humidity and higher temperatures. In other regions of Alaska having high rainfall (including southeast Alaska), 

covered drying could be beneficial, combined with longer drying times. Splitting 

firewood into sections can greatly accelerate air-drying rates.

Wood Measurements

A standard cord encloses a volume 4 ft by 4 ft by 8 ft (128 ft 3) and is a common 

method for selling wood by volume. Depending on the location, cordwood may be 

sold based on weight, loose volume, or stacked volume. In many North American 

jurisdictions, standards for sale and methods of measurements are defined by the 

Sealers of Weights and Measures. In Alaska, however, there are no formal standards in place. Selling cordwood based on green weight or dry weight is perhaps 

the most accurate method; however, many Alaska locations would be unlikely to 

have truck scales or necessary weighing equipment. Thus, accurate indirect methods would need to be developed for measuring wood volume, and then converting 

to weight by using reliable conversion factors for a given species.

The actual volume of fuel in a cord of wood may differ from about 60 to 110 

ft3 depending on the wood diameter, the form (split vs. unsplit), and the method of 

piling (e.g., air space between wood) (Bond 2008, Briggs 1994). In Alaska, 80 ft3

Figure 2—Slab wood fuel for high-efficiency burner 

at Dot Lake, Alaska.

Dave Frederick
GENERAL TECHNICAL REPORT PNW-GTR-783 

per cord has been used when estimating wood fuel properties of four commercial 

species (table 3). For a given volume of stacked cordwood, the weight could differ 

depending on species, wood moisture content, bark content, and average diameter 

among other factors. Thus, consistent procedures are needed for volume-to-weight 

conversions for Alaska species to ensure fair buyer-to-seller arrangements. Additional resources could include assistance from registered scalers who are trained 

to measure cordwood and involvement by the Bureau of Weights and Standards to 

develop measurement codes and standards. 

Table 3—Wood fuel heating values for Alaska species

Higher heating Gross heating Heat value

value at 0-percent value at 20-percent per cord

Species moisture content moisture content 80-ft3 basis 

BTUs per pound Million BTUs

Western redcedar (Thuja plicata Donn) 8,620 6,896 12.8

Western hemlock (Tsuga heterophylla (Raf.) Sarg.) 8,338 6,670 13.9

Sitka spruce (Picea sitchensis (Bong.) Carr.) 8,200 6,650 13.4

White (Englemann) spruce (Picea engelmannii 8,401 6,721 13.7

 Parry ex Engelm.)

BTU = British thermal unit.

Source: Miles 2006.

Wood Fuel Cost

Wood fuel cost can differ depending on Alaska region, and whether cordwood 

or sawmill slabs and edgings are used. Other variables affecting cordwood 

prices include species (hardwood vs. softwood), moisture content (seasoned vs. 

unseasoned), point of purchase (delivered vs. undelivered), wood size (split vs. 

unsplit), and wood length (e.g., 8 ft lengths vs. shorter).

On Prince of Wales Island in southeast Alaska (west of Ketchikan; see fig. 

1), cordwood prices were found to range from $75 to $160 per cord, with typical 

market prices of $100 to $125 (Miles 2006). More recent estimates indicate market 

prices of about $150 per cord (Peterson 2008). 

Farther north in Dot Lake, Alaska (near the town of Tok; see fig. 1), a market 

price of $125 per cord is common. Here, wood is delivered in 8 ft lengths and 

includes standing dead spruce (Frederick 2008). This wood is then cut to 32 to 38 

inches in length for use in cordwood burners. In the Glenallen, Alaska, area (see 

fig. 1), market prices as of May 2008 were close to $160 per cord for undelivered 

firewood (i.e., consumer picks up wood at a distribution point) (Veach 2008). In 

many cases, cordwood was small enough in diameter to burn as is (without the 

need for splitting).
Cordwood Energy Systems for Community Heating in Alaska—An Overview

In the Fairbanks, Alaska, area (see fig. 1), a local area supplier for solid fuels 

indicated current cordwood prices of about $200 per cord undelivered (or $225 per 

cord delivered) in May 2008. Discounted prices of about $160 per cord are possible 

for purchases of 10 cords at a time (about one truckload). In parts of interior Alaska, 

prices as high as $300 per cord are not uncommon (Elder 2007, Gorman 2008). 

These communities are not part of the road system and therefore must rely on local 

harvesting (or in some cases river transportation). An important consideration for 

users of high-efficiency systems would be whether established cordwood markets 

exist locally (vs. requiring a startup business to harvest, process, and transport 

cordwood). 

Wood Fuel Sizing

Wood sizing is an important consideration for high-efficiency cordwood systems, 

in order for pieces to easily fit within fireboxes. One commercial vendor (GARN) 

indicates firebox lengths ranging from 42 to 52 in on some of its models, and therefore cordwood length should be somewhat less than this (Frederick 2008). In some 

cordwood systems (fig. 3), 24-in-long sections are optimal; however, 32-in sections 

are possible while still maintaining good system operation (Frederick 2008). Larger 

units having a similar design could accommodate pieces 32 to 48 in long. 

Figure 3—High-efficiency cordwood energy system showing open firebox and burning embers 

(note that water storage reservoir surrounds firebox).

Daniel Parrent

An important 

consideration for 

users of highefficiency systems 

would be whether 

established 

cordwood markets 

exist locally.
10

GENERAL TECHNICAL REPORT PNW-GTR-783 

Another wood energy system vendor has three different cordwood boilers 

ranging from about 100,000 to 200,000 BTUs per hour (Tarm USA, Inc. 2003). 

Recommended cordwood length ranges from 18 to 21 in (i.e., maximum of 0.5 m) 

(Nichols 2008).

Pieces greater than 6 to 8 inches in diameter should be sectioned into smaller 

pieces, and pieces of various diameters should be included within a given charge to 

enhance efficiency (rather than burning cordwood of all one diameter) (fig. 4). For 

manually fed systems, the average length and diameter of individual pieces could 

also influence fuel loading and burning times, as can airflow into the combustion 

chamber.

Figure 4—Cordwood of various diameters are sectioned into smaller pieces in a covered storage area 

for a wood energy system in south-central Alaska. 

David Nicholls

Wood Species and Heating Values

Although the BTU energy per pound of dry wood is relatively constant, in practice, 

Alaska species differ considerably in their heating values (for both gross heating 

and recoverable heating). Recoverable heat is directly related to wood specific 

gravity. In Alaska, cottonwood (Populus spp.) is recognized as a lower density 

wood and Alaska yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) 

as a higher density wood. Alaska species are estimated to generate between 12.8 

and 13.9 million BTUs per cord, with hemlock (Tsuga spp.) providing the greatest 

amount of heat per cord. Gross heating values (at 20-percent moisture content) for 

selected Alaska species average between about 6,600 and 6,900 BTUs per pound 

(see table 3).
Cordwood Energy Systems for Community Heating in Alaska—An Overview

11

When evaluating manufacturers’ standards for cordwood systems, it is 

important to consider that tests are often done on eastern hardwoods having 

higher densities than most Alaska species. Therefore, greater volumes of Alaska 

woods may be needed to achieve equivalent results. However, softwoods are 

considered to have greater heating values per unit mass than hardwoods because 

softwoods normally have higher percentages of lignin. In some cases, essentially 

no performance issues have been noted in burning softwoods vs. hardwoods in 

cordwood systems (Frederick 2008), other than larger volumes of softwoods 

being needed.

Black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.) should not be 

considered a suitable species for cordwood energy systems, although it is found in 

abundance near many rural communities; many ecological factors related to climate 

change could affect regeneration rates of black spruce in interior Alaska, and 

therefore it is not known whether this species could be harvested sustainably (Barber 2008). An exception would be the use of black spruce salvaged from recently 

burned areas (i.e., this fuel source would be suitable for cordwood energy systems).

Wood Energy System Sizing

High-efficiency cordwood systems are not feasible for very small applications 

(displacing less than 500 gal per year of heating oil). These may be satisfied with 

domestic wood appliances, such as wood stoves or pellet stoves or furnaces 

(Parrent 2008). 

For larger systems, displacing between 500 and 2,000 gal per year, little or 

no savings would be expected with high-efficiency cordwood systems unless the 

following economic conditions are met (Miles 2006):

• They can be enclosed in an existing structure.

• Low-cost cordwood is available.

• Labor is free.

• Cost for a hot-water piping system between buildings is minimal.

Recent feasibility work in Alaska estimates the annual heating oil displacement 

for a large school (Delta Greely School in Delta Junction) to be 102,000 gal/yr 

(Fermann and Crimp 2007), a size that would most likely favor chip-fired systems 

rather than cordwood systems. A smaller school system (Copper Center Schools), 

displacing only 6,000 gal/yr, should be well suited for high-efficiency cordwood 

energy systems. The average heating oil displacement for six Alaska schools for 

which wood energy feasibility studies are underway is estimated to be 44,834 gal/

yr (Fermann and Crimp 2007). If wood energy systems were established at all six 
12

GENERAL TECHNICAL REPORT PNW-GTR-783 

of these schools, a mix of chip-fired systems and high-efficiency cordwood systems 

would probably produce the best results. 

An important consideration when sizing cordwood energy systems is whether 

wood will be the only fuel used (capable of meeting all heating needs, even on 

the coldest days), or whether a dual fuel system (e.g., heating oil and wood) will 

become part of the final project design. In this case, oil-fired boilers would be 

available for peak demand or as a backup system if the wood system were to fail. 

For most high-efficiency cordwood applications (such as Alaska schools), reliable 

backup systems will be necessary to provide heat if the wood energy system were 

to become inactive (e.g., owing to temporary shortages of cordwood or labor). 

Thus, wood energy adopters should be very cautious about using wood as their 

only fuel source. By using a heat exchanger, cordwood systems can supplement 

existing oil systems that would handle the peak loads. One way to reduce oil use is 

to increase the number of firings per day of wood. For example, a cordwood system 

in Dot Lake, Alaska, typically has about eight firings of wood per day during maximum heating needs (i.e., in midwinter). However, a similar system with increased 

insulation and optimal sizing might require only about three firings of wood per 

day, therefore requiring little or no use of oil as a secondary fuel (Frederick 2008). 

Operating and Maintenance Costs

The primary operating cost for high-efficiency cordwood systems is often wood 

fuel, often followed by labor costs. Labor is required to move cordwood from the 

storage area to the boiler building, to stoke (i.e., to load cordwood into) the boiler, to 

clean the boiler, and to dispose of ash. A reasonable assumption for most locations 

in Alaska is that the boiler will operate every day for 210 days (i.e., 30 weeks) per 

year between mid-September and mid-April (Parrent 2008). The actual daily labor 

requirements will depend on the number of stokings per day; however, a reasonable 

assumption is for each stoking to take 15 minutes or less.

In addition to fuel loading, other duties could include routine maintenance tasks 

such as removing ash, inspecting fans, and coordinating fuel arrivals. An important 

consideration is having a dedicated labor source available to “break away” from 

other responsibilities to give part-time attention to the wood energy system. Where 

dedicated labor cannot be ensured, a backup system (automatically switching to 

fuel oil as needed) could provide heat, as needed.

There is also an electrical cost component to the boiler operation. An electric 

fan creates an induced draft, enhancing combustion and contributing to higher 

boiler efficiencies. One estimate predicted fan electrical costs ranging from $100 to 

$200 per year, based on electrical costs of $0.30 per kilowatt hour (Parrent 2008). 
Cordwood Energy Systems for Community Heating in Alaska—An Overview

13

However, in many communities in interior Alaska, electrical costs of up to $0.50 

per kilowatt hour are not uncommon. The cost of operating circulation pumps 

would not be significantly different for wood energy vs. oil-fired systems.

Underground Piping

When heating multiple buildings, an important consideration is the cost of insulated 

underground piping needed to circulate hot water between buildings. Numerous 

other variables could be considered to optimize heat delivery, including:

• Number of buildings to heat and total area of buildings.

• Distance between buildings: a rule of thumb in interior Alaska is a maximum distance of 100 ft between the boiler and the most distant building. 

Shorter distances between buildings will allow use of smaller diameter 

(less expensive) pipes. A pipe diameter of 1.26 in is fairly common for 

smaller systems (Frederick 2008).

• Permafrost: in some regions of Alaska, frozen soil could affect construction costs and project feasibility. Aboveground insulated piping may be 

preferred to underground piping, such as the cordwood system recently 

installed in Tanana, Alaska (Frederick 2008).

• Piping materials used: several types of tubing are available for supply and 

return water. In one configuration, tubing is surrounded by insulation that 

is in turn encased within a corrugated high-density polyethylene jacket. 

Water can be piped in one direction (i.e., one pipe enclosed) or two directions (two pipes enclosed) for a given piping system. There are also many 

possible configurations of piping material, including “Microflex” (a hard 

jacket containing closed-cell polyethylene insulation), and also surrounding 

oxygen-barrier polyethylene (PEX) pipe (Frederick 2008). 

• Cost of piping materials: as a rule of thumb, each lineal foot of “hard 

piping” normally used in Alaska will cost about $70 to install, and 

crosslinked PEX piping will cost about $40 (Miles 2006). Current prices 

(i.e., 2008) are likely to be higher than this, given recent overall price 

increases. An important cost consideration is the diameter of the PEX 

piping, which typically ranges up to 2 in diameter. 

• Other considerations: pump size, thermal load (BTUs per hour), water temperature, and electrical use are other variables to consider when designing 

piping systems.

In some regions 

of Alaska, frozen 

soil could affect 

construction costs 

and project feasibility.
14

GENERAL TECHNICAL REPORT PNW-GTR-783 

Thermal Storage Capacity

In high-efficiency cordwood systems, the firebox can be stoked intermittently, and 

heat of combustion is transferred to water that is stored in a “jacket” surrounding 

the combustion chamber (see fig. 3). Thermal storage capacity of heated water is 

important because it influences the frequency of stoking and can be a factor in 

determining overall system efficiency. In general, larger fireboxes and/or water 

reservoirs will require less frequent stoking. An important advantage of highefficiency cordwood systems is that the wood energy benefits can be realized long 

after the fire in the firebox has died down (while heat is still available in the heated 

water). One commercial vendor indicates thermal storage capacities ranging from 

1,500 to 4,400 gal on some of its models (Dectra Corporation 2008). Other vendors 

will supply external tanks for water storage (Tarm USA, Inc. 2003). It should be 

noted that the use of thermal storage capacity within a water reservoir could be 

used with other fuel types (i.e., heating oil, diesel, propane, etc.) and would not be 

limited to wood fuel. 

Building Construction

Locations already having existing buildings in place (as well as readily available 

space for air-drying of cordwood) can have significant economic advantages over 

sites requiring new building construction. For example, a primary reason that the 

cordwood system in Dot Lake, Alaska, cost only $66,000 (Miles 2006) was that no 

new building construction was needed. In other cases, wood energy systems and 

buildings can be “bundled into” new construction projects, such as new schools. In 

rural Alaska, a reasonable assumption is that a pole barn could be constructed for 

fuel storage in addition to an enclosed boiler building. In other cases, more substantial structures may be needed. For example, three proposed cordwood systems in 

southeast Alaska (capacity 350,000 to 425,000 BTUs per hour) had building costs 

ranging from $6,500 to $21,600 (Miles 2006). It is not uncommon for the total cost 

of a cordwood energy system to be two to three times the cost of just the boiler.

Conclusions

This report reviews the feasibility of high-efficiency cordwood heating systems 

for use in Alaska communities by identifying several factors pertinent to their use. 

These systems could be well suited to utilize several types of biomass including 

cordwood, wood briquettes, small-diameter stems from hazardous fuel removals, 

or slabs and edgings from sawmills (but not bulk fuel sources such as sawdust or 

chips). 
Cordwood Energy Systems for Community Heating in Alaska—An Overview

15

A significant advantage of cordwood energy systems is their relatively low cost. 

Relatively low-cost options can be explored for heat distribution systems (by using 

underground pipes) and for buildings to house wood energy systems and provide 

covered storage for fuel. As fossil fuel prices increase, the economic incentives to 

consider low-cost wood energy solutions would become even greater.

The cordwood systems discussed in this report use relatively small volumes of 

wood (often a few hundred tons per year), and therefore present opportunities to 

sustainably harvest biomass from nearby areas. Numerous benefits could accrue 

from wood energy use in rural Alaska including increased cash economy, higher 

employment (for wood energy system operation and cordwood harvesting), and 

greater forest health in areas surrounding communities. 

Glossary2

biomass—The total volume of organic matter in a given area.

biomass boiler—A boiler that burns bark, sawdust, wood scraps, and other waste 

material. Also called a hogged-fuel boiler.

biomass harvesting—The practice of harvesting and using the entire tree, including 

the top, limbs, and stump, with the noncommercial portions generally chipped for 

fuel.

cordwood—Small wood or branches cut for firewood or to make charcoal.

firewood—1. Wood to be used as fuel. 2. Slang for short pieces used for crating, etc.

fuelwood—Wood salvaged from mill waste, cull logs, branches, etc., and used to 

fuel fires in a boiler or furnace.

roundwood—Logs, bolts, and other round sections as they are cut from the tree.

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 2.54 Centimeters

Feet (ft) .3048 Meters

Square feet (ft2) .0929 Square meters

Cubic feet (ft3) .0283 Cubic meters

Acres (ac) .405 Hectares

Gallons (gal) 3.78 Liters

British thermal units (BTUs) 1,050 Joules

Tons (t) 907 Kilograms

Pounds (lbs) 454 Grams

Ounces (oz) 28.4 Grams

2 Source: Random Lengths 2000.
16

GENERAL TECHNICAL REPORT PNW-GTR-783 

References

Barber, V. 2008. Personal communication. Assistant professor, Forest Products 

Program, University of Alaska-Fairbanks, Palmer Research and Extension 

Station, 533 E Fireweed Ave., Palmer, AK 99645. 

Bond, B. 2008. Selecting and using hardwood firewood. http://web.utk.edu/~tfpc/

publicat/fire.htm. (May 6, 2008).

Briggs, D. 1994. Forest products measurements and conversion factors. AR-10. 

Seattle, WA: University of Washington, Institute of Forest Resources. 168 p.

Dectra Corporation. 2008. GARN wood heating systems. http://garn.com/. 

(February 21, 2008).

Elder, L. 2007. Western Alaska firewood business plan. http://www.tananachiefs.

org/natural/AWEC2007.shtml. (May 6, 2008).

Fermann, K.; Crimp, P. 2007. Wood energy in Alaska—changing the way rural 

communities heat buildings [Poster]. In: Alaska rural energy conference; April 

2007; Fairbanks, Alaska.

Frederick, D. 2007. The GARN wood “boiler”—Dot Lake, Alaska. http://www.

tananachiefs.org/natural/AWEC2007.shtml. (May 6, 2008).

Frederick, D. 2008. Personal communication. Alaskan Heat Technologies, P.O. 

Box 2275, Dot Lake, AK 99737.

Gorman, R. 2008. Personal communication. Professor, University of AlaskaFairbanks, Cooperative Extension, 2221 E Northern Lights Blvd., Anchorage, 

AK 99508-4143.

Intertek Testing Services. 2006. Test of a solid fuel boiler for emissions and 

efficiency. Rep. No. 3087471. Prepared for State of Michigan, Air Quality 

Department, 420 Fifth Street, Gwinn, MI 49841.

McGrath Light and Power. 1999. McGrath biomass heating demonstration 

project. McGrath, AK: McGrath Light and Power, Inc. 14 p. 

Miles, T.R. 2006. Feasibility assessment for wood heating—final report. Prepared 

for Alaska Wood Energy Development Task Group. 80 p. http://jedc.org/forms/

AWEDTG_WoodEnergyFeasibility.pdf. (May 6, 2008).

Nichols, S. 2008. Personal communication. TARM USA Inc., P.O. Box 285, Lyme, 

NH 03768.
Cordwood Energy Systems for Community Heating in Alaska—An Overview

17

Olsen, P. 2007. Alaska village initiatives—managing forests for fuel and other 

values. http://www.tananachiefs.org/natural/AWEC2007.shtml. (May 6, 2008).

Parrent, D. 2007. Wood energy opportunities for Alaska. http://www.tananachiefs.

org/natural/AWEC2007.shtml. (May 6, 2008).

Parrent, D. 2008. Preliminary feasibility assessment for high efficiency, low 

emission wood heating in Ketchikan, Alaska. Prepared for M. Murphy, U.S. 

Department of Agriculture, Forest Service, Tongass National Forest. 31 p. 

Unpublished report. On file with: Daniel Parrent, 204 Siginaka Way, Sitka, 

AK 99835.

Peterson, K. 2008. Personal communication. Program assistant, Land Resources, 

University of Alaska-Fairbanks, P.O. Box 19190, Thorne Bay, AK 99919.

Random Lengths. 2000. Terms of the trade. 4th ed. Eugene, OR: Random Lengths 

Publications, Inc. 423 p.

State of Alaska. 2006. Current community conditions: fuel prices across Alaska, 

September 2006 supplement. Report to the Governor. Juneau, AK: Research and 

Analysis Section, Division of Community Advocacy, Department of Commerce, 

Community, and Economic Development. 21 p. 

State of Alaska. 2008. Alaska by region [Political]. Juneau, AK: Department of 

Commerce, Community, and Economic Development. http://www.dced.state.

ak.us/oed/student_info/learn/region.htm. (August 15, 2008).

Tarm USA, Inc. 2003. Wood gasification. http://www.woodboilers.com/woodgasification.asp. (May 6, 2008).

Veach, H. 2008. Personal communication. Program assistant, University of AlaskaFairbanks, Cooperative Extension, P.O. Box 756180, Fairbanks, AK 99775-6180. 
18

GENERAL TECHNICAL REPORT PNW-GTR-783
Pacific Northwest Research Station

Web site http://www.fs.fed.us/pnw/

Telephone (503) 808-2592

Publication requests (503) 808-2138

FAX (503) 808-2130

E-mail pnw_pnwpubs@fs.fed.us

Mailing address Publications Distribution

Pacific Northwest Research Station

P.O. Box 3890

Portland, OR 97208-3890
U.S. Department of Agriculture

Pacific Northwest Research Station

333 SW First Avenue

P.O. Box 3890

Portland, OR 97208-3890

Official Business

Penalty for Private Use, $300