Economic and Environmental Benefits 

of Community-Scale Cordwood Hydronic 

Heaters in Alaska—Three Case Studies

David L. Nicholls, Allen M. Brackley, and Daniel J. Parrent

United States Department of Agriculture

Forest 

Service

Pacific Northwest 

Research Station

General Technical Report

PNW-GTR-924

December

2015
Authors

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

research forester, Pacific Northwest Research Station, Alaska Wood Utilization 

and Development Center, 204 Siginaka Way, Sitka, AK 99835. Daniel J. Parrent

is a program manager, Biomass Utilization and Forest Stewardship, State and 

Private Forestry, Alaska Region, 161 East 1st Avenue, Door 8, Anchorage, AK 

99501.

Cover photos: Combustion chamber and cordwood system, by Jonathan 

Fitzpatrick; small-diameter cordwood in storage shed, by David Nicholls.

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Abstract

Nicholls, David L.; Brackley, Allen M.; Parrent, Daniel J. 2015. Economic 

and environmental benefits of community-scale cordwood hydronic heaters in 

Alaska—three case studies. Gen. Tech. Rep. PNW-GTR-924. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station. 

22 p.

Over the past decade, the use of wood for thermal energy in Alaska has grown significantly. Since 2000, nearly 30 new thermal wood-energy installations in Alaska 

have been established. Cordwood units, burning primarily firewood and other 

forms of roundwood, have played an integral part in this success and are well suited 

to many rural communities in Alaska. In this case study, we evaluate cordwood 

installations located in three geographic regions of Alaska. Included are systems at 

Coffman Cove (southeast Alaska), Ionia (Kenai Peninsula, Alaska), and Gulkana 

(south-central Alaska). 

We considered the wood-energy conversion process, system operation, 

economics, and carbon benefits of the three cordwood systems. We found that 

the simple payback period ranged from 1.1 to 14.2 years and the internal rate of 

return from 8 to 91 percent, and that benefits exceeded costs by a factor of from 

1.6 to 17. There were also substantial carbon benefits for cordwood systems. 

Carbon dioxide (CO2) emissions (relative to those from heating oil) differed by 

installation from 129 to 259 tons avoided per year, with total reductions of 611 

tons of CO2 per year. We also considered secondary benefits of community-scale 

cordwood energy systems in rural Alaska, including greenhouses for local foods, 

the ability to create part-time jobs for local residents, and the educational experiences for school students.

Keywords: Wood energy, cordwood, rural energy, net present value, 

CO2 emissions.
Contents

1 Introduction

2 Cordwood Use in Thermal Energy Systems—Small Industrial Scale

2 Wood-Energy Project Development

3 System Design and Operation

5 Case 1—Southeast Alaska (Coffman Cove)

5 System Overview

10 Coffman Cove, Alaska, Wood-Energy Economics

11 Coffman Cove, Alaska, Carbon Benefits

11 Case 2—South-Central Alaska (Ionia Community)

11 System Overview

12 Ionia Community Wood-Energy Economics

12 Ionia Community Carbon Benefits

13 Case 3—South-Central Alaska (Gulkana Village)

13 System Overview

15 Gulkana Village Wood Energy Economics

16 Gulkana Village Carbon Benefits

16 Discussion: Cordwood Energy Systems in Alaska

17 Conclusions

17 Tree Species Identified in This Report

18 Metric Equivalents

18 References

21 Appendix: Cordwood Historical Context
1

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Introduction

Over the past decade, the use of wood for thermal energy in Alaska has grown 

significantly. Confronted by high fuel costs, many rural communities have committed to the use of wood energy to displace fossil-fuel use. Since 2000, nearly 30 

new wood-energy systems have been installed in Alaska at schools, government 

buildings, and other community facilities. Several of these are cordwood systems 

(table 1). Important drivers spurring this growth have included construction funding by the Alaska Energy Authority (AEA) through the State of Alaska Renewable 

Energy Fund program, technical assistance by numerous partners and government 

agencies, and more than 150 prefeasibility studies. These have been supported by 

the Alaska Wood Energy Development Task Group, AEA, Alaska Village Initiatives, National Renewable Energy Laboratory, and the Tanana Chiefs Conference, 

among others. All of the wood-energy systems so far are thermal-energy systems. 

All provide heat to schools and community buildings. 

Cordwood energy systems—in contrast to wood chip or pellet systems—have 

played an integral role in pioneering Alaska’s wood-energy growth. Cordwood 

systems are relatively “low tech,” inexpensive systems that are robust and easy 

to operate, and which can provide community employment benefits for system 

operation and wood harvesting. They can also be used on a modular basis, with 

individual burners added as needed. Cordwood systems are often the most practical 

technology in very remote locations owing to the ready availability of wood and 

minimal processing requirements. In Alaska, this would include most locations 

south of the Brooks Range that are capable of growing trees large enough to be 

Table 1—Cordwood energy systems in Alaska as of May 2015a

Startup Number of

Location Host site date burners System type

Coffman Cove Howard Valentine Coffman 2010 2 GARN system

 Cove School

Elim Elim Water Plant 2012 1 GARNpak system

Fort Yukon University of Alaska Fairbanks 1 Tarm system

Gulkana Gulkana Village Council 2012 2 GARN cordwood, Tarm pellet 

Galena Galena Senior Center 3 Tarm Innova Solo system

Ionia Ionia, Inc. 2008 2 GARN system

Kasaan Kasaan School 2014 1 GARN system

Kokhanok Lake and Pen Borough 1 GARN system 

Tanana Tanana washeteria 2007 3 GARN/Econoburn systems

Tetlin Tetlin School 1 Tarm Innova Solo system 

Thorne Bay Thorne Bay School 2012 2 GARNpak cordwood system

Yakutat Tlingit-Haida Regional 1 WoodMaster/Woodgun

 Housing Authority

a

 Includes systems in-operation or under construction; does not include proposed systems.

Since 2000, nearly 

30 new wood energy 

systems have been 

installed in Alaska, 

including schools, 

government buildings, 

and other community 

facilities.
2

GENERAL TECHNICAL REPORT PNW-GTR-924

harvested for cordwood. Another important factor that varies widely throughout 

Alaska is precipitation. For example, in our study area, annual precipitation ranges 

from about 100 inches in Coffman Cove to about 11 inches in Gulkana.

In this report, we consider the wood-energy conversion process, system operation, economics, and carbon benefits of three community-scale cordwood systems 

across three Alaska regions. In many parts of rural Alaska, cordwood energy not 

only makes the most economic sense, but also returns the most benefits to the 

community. Some examples of benefits include greenhouses for local foods; local 

employment in wood harvesting, transportation, and use; and educational benefits 

to students in schools, which frequently are users of wood-energy systems.

Specific objectives of this report include conducting an economic analysis of 

all three cordwood systems and providing the context and background needed for 

future wood-energy users in Alaska to make informed decisions. Finally, we hope 

to demonstrate how cordwood energy can successfully meet community heating 

needs across Alaska, even when tree species, climate, and local operating conditions differ widely.

Cordwood Use in Thermal Energy Systems—

Small Industrial Scale

The terms cordwood, roundwood, and firewood are often used interchangeably. One 

cord of wood is defined as a stack of wood, well ranked and stowed, 4- by 4- by 

8-ft, including bark and air space. Depending on wood size, straightness, soundness, and other factors, the actual amount of fuel in a cord of wood varies between 

80 and 100 ft3. A cord of softwood or hardwood grown in Alaska typically weighs 

between 4,300 and 5,000 lbs. green weight depending on the species (Miles and 

Smith 2009, Wilson et al. 2010). The use of cordwood energy in small industrialscale systems, such as those discussed in this report, is similar to the residential use 

of firewood. It begins with the harvesting of roundwood, followed by splitting, drying, storage, and finally combustion. Whereas a typical home may burn 5 to 8 cords 

of wood per heating season, larger community heating systems in Alaska may burn 

more than 50 cords a year, depending on their size and heating needs. If scaling is 

necessary, then volume measurements using standard scaling equipment is the most 

efficient method. Typically, a ton of dry wood has the same energy content as about 

120 gal of fuel oil (Woodpellets.com 2015).

Wood-Energy Project Development

A typical wood-energy system (whether cordwood, chips, or pellets) generally 

includes the following planning steps:

In many parts of rural 

Alaska, cordwood 

energy not only makes 

the most economic 

sense, but also returns 

the most benefits to 

the community.
3

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

1. Preliminary economic feasibility study and conceptual design 

2. Phased, detailed design

3. Biomass resource assessment

4. Wood fuel type 

5. Financing/funding

6. Permitting (where necessary) and construction

7. Commissioning and operation

8. Project evaluation and feedback

Underlying all these steps is the need for strong community support and a 

“project champion.” In many ways, this support is the most important element for 

cordwood systems (compared to chip or pellet systems), owing to the greater labor 

requirements for wood harvesting, processing, and transporting, and the potential to 

create new employment.

System Design and Operation

In this report, cordwood systems are defined as being larger than residential scale 

but using similar wood-fuel sources. At this scale, cordwood systems are among the 

simplest wood-energy systems to construct and operate, in part because of the need 

for manual labor during all aspects of operation. Most cordwood systems use thermal storage to make heat available several hours after combustion. Thermal storage 

can be in the form either of a water jacket surrounding the combustion chamber or 

an external tank separate from the main burner. Some designs feature large thermal 

storage jackets (with capacities of between 1,000 and 4,000 gal) while other designs 

are more compact, with considerably less water storage. 

The basic process is similar for all cordwood systems. First, cordwood must 

be sized to fit the firebox. Typically, wood will be cut 2 to 4 inches shorter than the 

length of the firebox, with pieces greater than about 8 inches in diameter being split 

lengthwise. Then the operator “stokes” (i.e., manually loads) the firebox with wood 

(fig. 1). The labor needed to stoke the combustion chamber can, in some cases, be 

a limiting factor for cordwood use. Because manual handling of wood fuel can be 

a constraint for larger systems, a recommended maximum system size is 750,000 

British thermal units (Btus) per hour (Biomass Energy Resource Center 2015).

As wood combusts, heat is transferred to a working fluid (often water or glycol) 

and then to an end use, often via a heat exchanger. Routine maintenance includes 

manual ash removal and cleaning the boiler firetubes. High-efficiency combustion 

is aided by fans (either forced air or induced draft fans), which reduce the production of smoke and particulates. In this respect, it is important to distinguish between 

high-efficiency cordwood burners and low-efficiency firewood units, a topic of 
4

GENERAL TECHNICAL REPORT PNW-GTR-924

much attention in recent years. The distinction between high- and low-efficiency 

cordwood burners has been particularly important in municipalities that have airquality problems, such as Fairbanks, Alaska.

One of the key operating decisions is whether to construct a modular system 

that has more than one cordwood burner, versus a single cordwood burner. An 

advantage of having more than one burner is the ability to heat with all units during periods of peak demand while using fewer burners during the fall and spring 

“shoulder” seasons. This can be important in Alaska, where shoulder seasons may 

still experience very cold weather. Cordwood burners may also be used to heat 

numerous buildings via a district heating loop, as in Gulkana, Alaska (see “Case 

3” on p. 13). For single cordwood burners, scales of operation are generally limited 

to about 100 cords of wood per year, the equivalent of about twice the wood used 

at Coffman Cove (see “Case 1” below). The labor requirements to manually handle 

Figure 1—Many cordwood systems are designed to burn wood in an intense flame, quickly transferring heat to a water jacket 

surrounding the burn chamber. Note that in normal operation the door to the combustion chamber would be closed.

Jonathan Fitzpatrick
5

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

100 cords of wood per year could also be a limiting factor in some communities. 

Lastly, some communities might be limited in the amount of wood that they could 

sustainably provide from nearby forested areas, resulting in the use of fewer than 

100 cords per year.

Note that commercial cordwood hydronic heaters are not just scaled-up wood 

stoves like those typically found in residential applications. Commercial systems 

usually have induced draft fans and large thermal storage capacity. The pairing of a 

“hot and fast” wood-burning period followed by several hours of thermal storage is 

critical for efficient cordwood use. 

Case 1—Southeast Alaska (Coffman Cove)

System Overview

The Southeast Island School District (SISD), on Prince of Wales Island in southeast 

Alaska, oversees the operation of 10 rural schools. In 2010, the district’s Howard 

Valentine School in Coffman Cove installed two GARN1 units (Dectra Corporation 

2015), making it the first user of a cordwood system on Prince of Wales Island. The 

school has recently completed its fourth heating season. 

In 2012, SISD installed two prototype “GARNpak” hydronic heaters at 

Thorne Bay School in Thorne Bay, and in 2014 the district installed one GARN 

unit at Barry C. Stewart Kasaan School in Kasaan (Fitzpatrick 2015). GARN systems use a two-stage gasification process and are unpressurized. Therefore, they 

cannot be connected directly to a pressurized system without a heat exchanger 

(Ehrlich 2015). For the remainder of this case study, we focus on the Coffman 

Cove cordwood system. 

Coffman Cove was motivated to pursue cordwood energy by several factors, 

including high fuel costs and an abundance of local wood wastes and forest harvesting residues. Between 2010 and 2014, wood usage in the Coffman Cove system 

has ranged from 30 to 55 cords per year, with recent usage of 52 cords in a single 

heating season (Fitzpatrick 2015). Their cordwood burner typically operates from 

September through June and provides heat to the school (9,480 ft2) as well as to 

its domestic hot water system. In the near future, the cordwood system will also 

provide heat for a greenhouse (6,000 ft2) and a teacher housing facility (4,000 ft2). 

As with most cordwood systems, fuel is hand fed into the boilers daily. At the peak 

of the winter heating season, the boiler needs to be “stoked” up to six times a day, 

while on warmer days during spring and fall only two or three times per day. The 

system is typically not used during summer months. 

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.

Coffman Cove was 

motivated to pursue 

cordwood energy 

by several factors, 

including high 

fuel costs and an 

abundance of local 

wood wastes and 

forest harvesting 

residues.
6

GENERAL TECHNICAL REPORT PNW-GTR-924

The Coffman Cove wood-energy system includes two GARN WHS-2000 

cordwood burners. An integrated hydronic tank stores thermal energy from a fast 

wood burn, which is then available over a period of several hours before the need to 

re-stoke the combustion chamber. 

Each of Coffman Cove’s two GARN boilers has a rated output of about 325,000 

Btus per hour. Additional energy requirements include a 1-HP circulation pump. 

Their wood supply is stored in a covered building with a capacity of about 150 

cords. Heat is distributed via underground piping (fig. 2) from the GARN units to 

the school, a distance of less than 150 ft. Coffman Cove’s initial system cost was 

close to $424,000, which included all engineering and design work. Their ongoing 

maintenance (which includes parts and minor repairs) is only about $500 per year. 

Figure 2—Cross section of insulated piping for water distribution, showing layered construction and 

supply and return pipes, normally buried underground.

Cordwood resources are accessible in most Alaskan communities and have the 

added benefit of increasing employment, not only through cordwood collection, but 

also wood splitting and stoking. Coffman Cove’s system burns western hemlock (60 

percent of total), Sitka spruce (30 percent of total), and Alaska yellow-cedar or red 

alder (10 percent of total). Firewood is procured from local individuals as well as 

one small business devoted to firewood production. The economic benefits to communities on Prince of Wales Island are notable. About 10 to 15 part-time jobs have 

been created, with individuals supplying firewood, typically one cord at a time. 

Other community benefits include students raising money for sports and academic 

travel by stacking firewood. An additional benefit is that the boiler room provides 

heat to community members for tanning hides and for hatching chicken eggs in 

incubators (fig. 3).

Jonathan Fitzpatrick

The economic benefits 

to communities on 

Prince of Wales Island 

are notable. About 10 

to 15 part-time jobs 

have been created, with 

individuals supplying 

firewood, typically one 

cord at a time. 
7

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

The Coffman Cove system managers are well aware of the need to dry their 

cordwood before burning. They have constructed a separate fuel storage building 

(fig. 4), where they split, stack, and dry the wood for up to 12 months, allowing it 

to reach 15 to 20 percent moisture content. Four-feet-in-diameter fans accelerate 

airflow through the covered storage building. Finally, smaller parcels of wood are 

placed in the boiler room for additional drying just before burning.

Figure 3—Construction completed for cordwood system in Coffman Cove, Alaska.

Figure 4—Covered cordwood storage in Coffman Cove, Alaska.

Jonathan Fitzpatrick Jonathan Fitzpatrick
8

GENERAL TECHNICAL REPORT PNW-GTR-924

Cordwood Drying in Southeast Alaska

In southeast Alaska, wood drying can require careful attention whether the end 

use is wood energy or solid wood products such as lumber. Wood-energy applications are especially sensitive to how well the fuel has been dried, because the 

amount of usable British thermal units (Btus) are directly related to moisture content. For example, while oven-dry wood has a heating value of about 8,600 Btus 

per lb, the same quantity of wood at 20-percent moisture content green basis will 

provide only 7,100 Btus per lb. (Stelzer 2015). In southeast Alaska, the need for 

effective air drying is especially important, because the most prevalent wood here 

(western hemlock) has a very high green moisture content of up to 63 percent for 

sapwood, and an overall moisture content of close to 50 percent (USDA FS 1999). 

The differences in gross heating value between fresh-cut wood and properly dried 

wood can be substantial—in some cases close to 8 million Btus per cord (table 2).

In almost all cordwood energy applications, wood moisture should be reduced 

to about 20 percent moisture content green basis before burning. In practice, this is 

usually done by air drying, either outdoors or in a covered structure, or fan-aided 

drying in a shed. One leading manufacturer of cordwood burners recommends 

air-drying cordwood for a full year to reach a target of 18- to 28-percent moisture 

content. They also recommend splitting wood 8 to 12 inches in diameter into 

halves, and wood larger than 12 inches into quarters (Dectra Corporation 2013). 

Simpson (1998) reported that 3 or 4 months of drying in well-ventilated and 

covered storage areas in southeast Alaska produce wood with 17 to 19 percent 

moisture content dry basis. In southeast Alaska, equilibrium moisture contents 

typically range between 15 and 20 percent (table 3). In other words, no amount 

Table 2—Cordwood properties of select Alaskan species, at 

time of harvest

Gross Gross heating

Average heating value,

green value, green 20-percent

Species weight condition moisture content

Pounds per BTUs BTUs

cubic foot per cord per cord

Sitka spruce 34.67 10,600,084 16,960,134

Western hemlock 39.4 12,778,120 20,444,992

Alaska yellow-cedar 39.38 14,327,853 22,924,565

Red alder 34.68 10,596,997 16,955,195

White spruce 34.67 11,633,919 18,614,271

Black spruce 35.65 11,350,678 18,161,085

Source: Simpson (1991) and Wilson et al. (2010).
9

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

of air drying at ambient temperatures can reduce 

wood moisture to less than about 15 percent, even 

after months of air drying at ambient temperatures. 

Empirical studies conducted in southeast Alaska 

evaluated Sitka spruce and western hemlock logs 

harvested in southeast Alaska. For logs that were 

peeled of bark and stored indoors, moisture contents 

between 20- and 30-percent oven-dry basis were possible after 12 months (Nicholls and Brackley 2010). 

Specific cordwood drying practices to enhance 

air-drying include:

• Covered storage (shed, pole barn, or similar 

structure).

• Covered storage with fans to increase airflow 

through wood.

• Wood splitting prior to drying (for larger stems).

• Drying a limited amount of wood in a small hopper near the combustion unit 

(fig. 5).

• Drying cordwood in a fully functioning dry kiln (often used to dry lumber).

• Cutting wood to uniform lengths to fit fireboxes—split to promote drying from 

the longitudinal surface.

• Covered storage 

(shed, pole barn, 

or similar structure) with racks 

that allow spacing between the 

piles. Keep wood 

shielded from rain 

and snow, but do 

not wrap with plastic or tarps (which 

could impede air 

circulation).

Table 3—Equilibrium moisture 

content for Juneau, and 

Ketchikan, Alaska, by month 

of year

Month Juneau Ketchikan

January 16.5 22.5

February 16.0 21.0

March 15.1 20.8

April 13.9 19.7

May 13.6 17.2

June 13.9 17.6

July 15.1 18.3

August 16.5 19.8

September 18.1 22.1

October 18.0 21.9

November 17.7 18.3

December 18.1 22.0

Source: Simpson 1998 (Juneau data); 

https://weather-warehouse.com/ 

(Ketchikan data).

Figure 5—Fuel storage and loading area, Coffman Cove, Alaska. The 

final stages of wood drying take place in this room.

Jonathan Fitzpatrick
10

GENERAL TECHNICAL REPORT PNW-GTR-924

Coffman Cove, Alaska, Wood-Energy Economics

RETScreen® software (RETScreen International 2015) was used to evaluate the 

economic benefits associated with wood energy (compared to heating oil). The 

primary RETScreen inputs are summarized in table 4. Net present value varied 

from $236,895 to $647,381, depending on the assumed heating oil cost (table 5). 

Similarly, the internal rate of return varied from 8.1 to 13.8 percent. Simple payback 

(in terms of years to first positive cashflow) ranged from 8.7 to 14.2 years, and the 

benefits exceeded costs by a factor of from 1.56 to 2.53. The base case for heating oil costs was $4.00 per gallon. Note that for all three locations we assumed a 

fuel cost escalation rate of 2 percent annually, an inflation rate of 3 percent, and a 

discount rate of 4 percent (table 4).

Table 4—RETScreen® inputs for wood-energy economic analysis of three cordwood 

systems in Alaska

Location

Input Units Coffman Cove Ionia Gulkana

Building structure 1 building 1 building 9 community

(school) (longhouse) buildings

Process water? Yes/no Yes Yes No

Cordwood burners 2 GARNsa 2 GARNs 2 GARNs

Heated area Square feet 9,800 12,000 12,000

Domestic hot Percentage of total 15 15 0

 water demand

Heating load BTUs per square feet 40 55 70

 per hour

Base case system Fuel type Heating Heating Heating 

oil #6 oil #6 oil #6

Base case — Dollars per gallon 4.00 4.50 5.00

 fuel cost

Base case — Percent 85 85 85

 efficiency

Wood fuel cost Dollars per ton 80 50 125

Wood fuel type Waste wood/ Waste wood/ Waste wood/

mixed softwood mixed softwood mixed softwood

Total initial costsb Dollars 424,000 115,000 898,000

Peak load system Not required Not required Not required

Operation and Dollars per year 600 1,200 800

 maintenance costs

Salvage value Dollars 0 10,000 10,000

Project life Years 25 25 25

System efficiency Percent 75 75 75

 (wood energy)

Fuel cost Percent 2.0 2.0 2.0

 escalation rate

Inflation rate Percent 3.0 3.0 3.0

Discount rate Percent 4.0 4.0 4.0

a

 Dectra Corporation (2013).

b

 Includes cost of feasibility studies, engineering, design, buildings, piping, and wood energy system.
11

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Coffman Cove, Alaska, Carbon Benefits

RETScreen software was also used to evaluate the carbon benefits associated with 

wood energy (versus heating oil). The Coffman Cove system had a carbon benefit 

of 129.3 tons of CO2 avoided, compared to a conventional fuel oil system providing 

the same heating load (table 5).

Case 2—South-Central Alaska (Ionia Community)

System Overview

Ionia is a residential mental health treatment center located on the Kenai Peninsula 

in Kasilof, Alaska. The center installed two separate wood-fired hot water boiler 

systems in 2008. This wood energy system results in energy savings of about $1,000 

per month in terms of propane cost avoided and about $150 per month of fuel oil 

Table 5—Economic results for Coffman Cove, Ionia, and Gulkana Village cordwood energy systems

Fuel oil cost (heating oil #6)

Coffman Cove Schools Ionia Community Gulkana Community

 Lowa Midb Highc Lowa Midb Highc Lowa Midb Highc

Result Units ($3.20/gal) ($4.00/gal) ($4.80/gal) ($3.60/gal) ($4.50/gal) ($5.40/gal) ($4.00/gal) ($5.00/gal) ($6.00/gal)

Pre-tax Percent 8.1 11.1 13.8 58.9 74.9 90.8 9.1 12.5 15.6

 internal

 rate of

 return

Simple Years 14.2 10.8 8.7 1.8 1.4 1.1 12.8 9.6 7.7

 payback

 period

Equity Years 11.7 9.3 7.7 1.7 1.4 1.1 10.7 8.4 6.9

 payback

 period

Net Dollars 236,895 442,138 647,381 1,136,501 1,489,607 1,842,713 640,866 1,152,227 1,663,587

 present

 value

Annual Dollars 15,164 28,302 41,440 72,750 95,353 117,956 41,023 73,756 106,489

 life- per

 cycle year

 savings

Benefit 1.56 2.04 2.53 10.87 13.94 17.01 1.71 2.28 2.85

 to cost 

 ratio

Carbon Tons 129.3 129.3 129.3 222.8 222.8 222.8 258.6 258.6 258.6

 dioxide per

 emissions year

 savings (vs.

 heating oil)

a

 Average fuel cost minus 20 percent.

b

 Average fuel cost (current April 2015).

c

 Average fuel cost plus 20 percent.
12

GENERAL TECHNICAL REPORT PNW-GTR-924

savings. Projected annual energy savings are 1,500 gal of fuel oil and 8,200 gal of 

propane (WFLC 2008). Several buildings are connected to the wood-energy system 

with 120 ft of super-insulated pipe that has been buried to a depth of 10 ft. 

During winter months, both cordwood units are typically in operation, with 

single units used during the shoulder seasons. During the 2015 heating season, 

about 200 lbs of wood per day typically were burned (about half a cord per week). 

However, on the coldest days, up to 300 lbs can be burned. Ionia can also vary its 

fuel use by firing the burners at either a “high dose” or “low dose.” A typical firing 

pattern would be to start with a normal “dosage” of about 100 lbs of wood in each 

burner (with doses of about 100 lbs 1 to 2 hours later) (Eller 2015). An advantage of 

operating only one burner is that only 2,000 gal of water need to be heated (versus 

4,000 gal when operating both burners). 

The Ionia community practices good stewardship by planting about 1,000 

trees per year (primarily lodgepole pine and western larch) for wood energy and 

other forest products. As of 2015, they have planted close to 5,000 trees, which are 

expected to be ready for cordwood burning within about 20 years.

Ionia Community Wood-Energy Economics

RETScreen software was used to evaluate the economic benefits associated with 

wood energy (versus heating oil). The primary RETScreen inputs are summarized 

in table 4. Net present value ranged from $1,136,501 to $1,842,713, depending on the 

assumed heating oil cost (table 5). Similarly internal rate of return ranged from 58.9 

to 90.8 percent. Simple payback period (in terms of years to first positive cash flow) 

ranged from 1.1 to 1.8 years, and the benefits exceeded costs by a factor of from 

10.87 to 17.01.

Ionia had by far the most attractive economics of any of the three cordwood 

facilities. This was primarily because of their low cost of wood (much of it being 

harvested locally) as well as essentially free labor to load cordwood. Their relatively 

low system cost ($115,000) also was instrumental in the high benefit-to-cost ratios. 

The base case for heating oil costs was $4.50 per gallon. Because of a bark beetle 

infestation in the early 2000s, Ionia has been able to benefit from a ready supply of 

low-cost and low-moisture-content wood.

Ionia Community Carbon Benefits

RETScreen software was used to evaluate the carbon benefits associated with wood 

energy (versus heating oil). The Ionia system had a carbon benefit of 223 tons of 

CO2 avoided annually, compared to a conventional fuel-oil system providing the 

same heating load (table 5). 

Lonia had by far 

the most attractive 

economics of any of 

the three cordwood 

facilities, primarily 

because of its low cost 

of wood (much of it 

harvested locally) as 

well as essentially free 

labor to load cordwood.
13

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Case 3—South-Central Alaska (Gulkana Village)

System Overview

Gulkana Village is an Alaska Native community (population 143) located in 

Gulkana, Alaska, about 14 mi north of Glenallen, Alaska. In 2010, Gulkana Village 

received a $500,000 grant from the State of Alaska’s Renewable Energy Fund to 

install two cordwood boilers that went into service later that year, providing heat for 

nine community buildings. The system has used 43 cords of wood per year (Anon. 

2012). The total project cost was $898,000.

In Gulkana Village, the cordwood production (a process that includes harvest, 

splitting, and drying) provides important employment benefits. Further, Gulkana 

is located within a fire-prone forest region and much of the community’s wood fuel 

needs are provided by wildfire prevention and mitigation measures. Gulkana Village has two GARN cordwood systems (model WHS-2000 hydronic boilers) located 

side by side, allowing them to be coordinated for use during shoulder seasons and 

also during mid-winter (fig. 6). Each burner is rated at 325,000 Btus per hour, burning cordwood harvested from local lands. 

Figure 6—Front view of modular cordwood energy system, showing two independent units side by 

side (Gulkana Village Council, Gulkana, Alaska). Note that during normal operation the doors would 

be closed.

David Nicholls

Gulkana is located 

within a fire-prone 

forest region and much 

of the community’s 

wood fuel is provided 

by wildfire prevention 

and mitigation 

measures.
14

GENERAL TECHNICAL REPORT PNW-GTR-924

Gulkana also installed a pellet boiler to supplement the community’s cordwood 

system. And, as of early 2014, a small pellet manufacturing system is under construction. Using locally harvested wood, the community soon expects to have the 

option of producing their own pellets, burning cordwood, or combinations of both. 

Gulkana Village uses a district heating system to heat nine community buildings 

that include four duplexes, a teen recreation center, a community hall with administrative offices, a fitness center, a maintenance shop, new offices, a community 

clinic, and a new bus garage (ACEP, n.d.) (fig. 7). The four duplexes are owned by 

the Copper River Housing Authority, which purchases heat from Gulkana Village.

During the system start-up in October and November 2010, the two boilers 

burned about 25 cords of wood, primarily white spruce (Picea glauca). A total of 

2,963 gal of heating oil were displaced for a savings of $10,933 (ACEP, n.d.). The 

Gulkana wood-energy system is located in interior Alaska, where winter temperatures can sometimes reach -50 °F. Therefore, proper sizing of the combustion equipment and a reliable wood fuel supply are critical elements. Most of the cordwood 

Figure 7—Aerial view of Gulkana Village, showing site of cordwood system and building heated (the distance between 2nd and 3rd St. is 

approximately 200 feet). Source: Google Maps®.

The Gulkana woodenergy system is 

located in interior 

Alaska, where winter 

temperatures can 

sometimes reach 

-50 °F. Therefore, 

proper sizing of the 

combustion equipment 

and a reliable wood 

fuel supply are critical 

elements.
15

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

is stored in a covered building, and is still in round form (fig. 8). Further, reliable 

pumps and circulation equipment are important (as water will quickly freeze at 

these temperatures). 

Gulkana Village Wood-Energy Economics

RETScreen software was used to evaluate the economic benefits associated with 

wood energy (versus heating oil). The primary RETScreen inputs are summarized 

in table 4. Net present value ranged from $640,866 to $1,663,587, depending on the 

assumed heating oil cost (table 5). Similarly, the internal rate of return ranged from 

9.1 to 15.6 percent. Simple payback period (in terms of years to first positive cash 

flow) ranged from 7.7 to 12.8 years, and benefits exceeded costs by a factor of from 

1.71 to 2.85. The base case for heating oil costs was $5.00 per gallon.

The Gulkana project economics were comparable to that of the Coffman Cove 

system. Despite having a considerably higher initial cost, the Gulkana system 

displaces more expensive heating oil, in addition to heating a greater number of 

buildings. Together, these factors offset the high initial capital cost.

Figure 8—Small-diameter cordwood in storage shed (Gulkana, Alaska). 

David Nicholls
16

GENERAL TECHNICAL REPORT PNW-GTR-924

Gulkana Village Carbon Benefits

RETScreen software was used to evaluate the carbon benefits associated with wood 

energy (versus heating oil). The Gulkana system had a carbon benefit of 259 tons 

of CO2 avoided annually, compared to a conventional fuel-oil system with the same 

heating load (table 5). 

Discussion: Cordwood Energy Systems in Alaska

Cordwood energy has proven viable for community heating in rural Alaska, with 

12 systems established as of 2015, including those that were operational or under 

construction. There are cordwood burners in all regions of Alaska (interior, southcentral, and southeast), with wood sources that include most major forest types. 

They are simple in design and generally appropriate for smaller facilities (i.e, 

facilities that use less than 10,000 gal of fuel oil annually). In many cases, more 

than one cordwood burner is housed at a given site because they can be installed 

together to meet even larger thermal energy loads. Most cordwood systems operate 

on the principle of storing combustion energy in a thermal water jacket that ranges 

in volume from a few hundred to several thousand gallons. Cordwood systems 

can heat multiple buildings via simple district heating loops, usually buried underground. This way, multiple uses can be accommodated—for example, heating a 

school, greenhouse, and teacher housing with a single system.

Cordwood burners can represent an ideal option for small remote villages, and 

in some aspects, they resemble residential cordwood systems. The fuelwood harvesting and delivery can be combined with residential firewood programs, offering 

synergies and opportunities for cooperation. Cordwood systems can be well suited 

to communities with no forest products infrastructure (i.e., no local sawmill), but 

with a well-developed network of residential users. In practice, simple procedures 

can aid successful operation, including splitting firewood to appropriate sizes for 

the burner and drying to recommended moisture levels before burning. Cordwood 

burners can supplement an existing residential firewood industry while creating 

additional employment.

New innovations are enabling use of cordwood systems in even the remotest 

Alaskan communities and villages. For example, the “GARNpak” design consists 

of modular, self-contained construction that is easily transported to remote locations and is easy to install. As the name suggests, this product comes as a complete 

package that includes primary pump, heat exchanger, piping, controls, and electrical connections (with some components being pre-piped and pre-wired) (Alaska 

Energy Associates 2012). After a concrete slab is ready, the “GARNpak” can be 

lowered in place with a lift truck, and final connections completed usually in 1 to 2 

days. 

New innovations 

are enabling use of 

cordwood systems 

in even the remotest 

Alaskan communities 

and villages. For 

example, the 

“GARNpak” design 

consists of modular, 

self-contained 

construction that is 

easily shipped to and 

installed in remote 

locations.
17

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Perhaps the greatest benefit to rural Alaskan communities is the employment 

benefits that relatively “low-tech” cordwood systems can bring. Cordwood systems 

seem to thrive where there is a strong village or community structure. In remote 

areas where forest resources are marginal or in high-latitude locations, it is important to complete a comprehensive resource analysis to ensure that cordwood supplies are sustainable. 

Conclusions

Cordwood-energy systems can be an ideal way for rural communities in Alaska to 

realize energy independence while establishing relatively simple energy systems. 

Wood-energy conversion, operation, project economics, local employment, and 

carbon benefits are all integral aspects of cordwood systems. Cordwood systems are 

economically feasible in most forested regions in Alaska ranging from southeast 

Alaska to interior Alaska (including some locations north of the Arctic Circle). 

Cordwood systems work well for a variety of species; however, key practices such 

as splitting large sections of wood and sufficient drying are important practices 

sometimes overlooked. Significant carbon savings are possible when cordwood 

is substituted for fossil fuels such as heating oil, such as in the three systems 

described in this report. Broader implications can be drawn beyond these three 

systems because nearly a dozen cordwood systems are now in operation in Alaska. 

The findings from this report are even more significant when one considers that 20 

wood-energy systems are now in operation in Alaska, and many of these are larger 

than the cordwood systems described in this report (likely having greater economic 

and carbon benefits). Lastly, energy self-sufficiency, local economic benefits, and 

educational benefits are often important byproducts of cordwood energy systems, 

as demonstrated by these case studies.

Tree Species Identified in This Report

Common name Scientific name

Alaska yellow-cedar Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little

Black spruce Picea mariana (Mill.) Britton, Sterns & Poggenb.

Red alder Alnus rubra Bong.

Sitka spruce Picea sitchensis (Bong.) Carrière

Western hemlock Tsuga heterophylla (Raf.) Sarg.

White spruce Picea glauca (Moench) Voss
18

GENERAL TECHNICAL REPORT PNW-GTR-924

References

Anon. 2012. Gulkana community energy plan. http://www.coppervalley.org/sites/

default/files/Gulkana%20Community%20Energy%20Plan%20Draft%202.pdf. 

(27 April 2015).

Alaska Center for Energy and Power [ACEP]. [N.d.]. Gulkana biomass. 

http://energy-alaska.com/gulkana-biomass. (28 April 2015).

Alaska Energy Associates. 2012. Venetie Village Council—level two biomass 

feasibility study. 37 p. http://www.akenergyauthority.org/Content/Programs/

AEEE/Biomass/Documents/PDF/Venetie2012.pdf. (19 August 2015).

Biomass Energy Resource Center. 2015. Heating systems—cordwood. http://

www.biomasscenter.org/what-we-do/our-expertise/heating-systems-cordwood. 

(15 July 2015).

Bruce, D.B.; Schumacher, F.X. 1950. Forest mensuration. 3rd ed. New York: 

McGraw-Hill. 483 p.

Dectra Corporation. 2013. GARN®WHS 1000/1500/2000 owner’s manual. 

http://www.garn.com/garn-whs-manuals/. (27 April 2015).

Dectra Corporation. 2015. GARN wood heating systems. http://www.garn.com/. 

(18 August 2015).

Ehrlich, B. 2015. GARN wood-fired hydronic heaters. http://greenspec.

buildinggreen.com/product/garn-wood-fired-hydronic-heaters/dectracorporation/9727. (27 April 2015).

Metric Equivalents

When you know: Multiply by: To find:

Inches 2.54 Centimeters

Feet (ft) 0.3048 Meters

Miles (mi) 1.609 Kilometers

Square feet (ft2) 0.0929 Square meters

Cubic feet (ft3) 28.3 Liters

Pounds (lb) .454 Kilograms

Tons (ton) .907 Tonnes or megagrams

Gallon (gal) .378 Liters

British thermal units (Btu) .000948 Joules

Degrees Fahrenheit .56 (°F) - 32 Degrees Celsius
19

Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Eller, T. 2015. Personal communication. Project manager, Ionia, Inc. 54932 

Burdock Road, Kasilof, AK 99610.

Fitzpatrick, J. 2013. Biomass: technology update—Thorne Bay and Coffman 

Cove Schools GarnPac and cordwood systems. http://www.akruralenergy.

org/2013/2013_REC_Thorne%20Bay%20School%20GarnPac%20and%20

Cordwood%20Systems_Jonathan%20Fitzpatrick.pdf. (27 April 2015).

Fitzpatrick, J. 2015. Personal communication. Project manager, Southeast Island 

School District, P.O. Box 19569; 1010 Sandy Beach Rd., Thorne Bay, AK 99919. 

Fonseca, M.A. 2005. The measurement of roundwood—methodologies and 

conversion ratios. Trowbridge, United Kingdom: CABI Publishing. 269 p.

Husch, B.; Miller, C.I.; Beers, T.W. 1982. Forest mensuration. 3rd ed. New York: 

John Wiley & Sons. 402 p.

Miles, P.D.; Smith, W.B. 2009. Specific gravity and other properties of wood and 

bark for 156 tree species found in North America. Res. Note NRS-38. Newtown 

Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research 

Station. 35 p.

Miles, T.R. 2006. Feasibility assessment for wood heating—final report. 81 p. 

http://www.jedc.org/forms/AWEDTG_WoodEnergyFeasibility.pdf. 

(27 April 2015).

Nicholls, D.L.; Brackley, A.M.; Barber, V. 2010. Wood energy for residential 

heating in Alaska: current conditions, attitudes, and expected use. Gen. Tech. 

Rep. PNW-GTR-826. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station. 30 p.

RETScreen International. 2015. Software suite. Ottawa, Ontario, Canada: Natural 

Resources Canada. http://www.retscreen.net/ang/home.php. (27 April 2015).

Simpson, W.T., ed. 1991. Dry kiln operator’s manual. Agric. Handb. 188. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 

274 p. 

Simpson, W.T. 1998. Equilibrium moisture content of wood in outdoor locations in 

the United States and worldwide. Res. Note FPL-RN-0268. Madison, WI: U.S. 

Department of Agriculture, Forest Service, Forest Products Laboratory. 11 p.
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GENERAL TECHNICAL REPORT PNW-GTR-924

Stelzer, H.E. 2015. Wood fuel for heating. Columbia, MO: University of Missouri 

Extension. 6 p. http://extension.missouri.edu/p/g5450. (27 April 2015).

U.S. Department of Agriculture, Forest Service [USDA FS]. 1999. Wood 

handbook—wood as an engineering material. Gen. Tech. Rep. FPL-GTR-113. 

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products 

Laboratory. 463 p.

Western Forestry Leadership Coalition [WFLC]. 2008. From wood waste 

to renewable energy: a summary report of wood utilization efforts in heating 

systems in the western United States and territories. 18 p. http://wflccenter.org/

news_pdf/295_pdf.pdf. (9 September 2015).

Wilson, P.L.; Funck, J.W.; Avery, R.B. 2010. Fuelwood characteristics of 

northwestern conifers and hardwoods. Updated by Parrent, D.J.; Funck, J.W.; 

Reeb, J.; Brackley, A.M., eds. Gen. Tech. Rep. PNW-GTR-810. Portland, OR: 

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

Station. 50 p. (First published in 1987 as Res. Bull. 60. Corvallis, OR: Oregon 

State University, College of Forestry, Forest Research Laboratory.)

Woodpellets.com http://www.woodpellets.com/support/fuel-savings-calculator.

aspx. (19 August 2015).
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Economic and Environmental Benefits of Community-Scale Cordwood Hydronic Heaters in Alaska—Three Case Studies

Appendix: Cordwood Historical Context

Historically, firewood and pulpwood are two products that were measured by the 

cord. Most mensurational texts (Bruce and Shumacher 1950, Fonseca 2005, Husch 

et al. 1982) identify a cord as a pile of wood cut into 4-ft sticks that is 4 ft tall and 8 

ft in length. What none of these authors note, however, is that there was an endless 

variation in how mills in the 20th century placed additional detail on how the 4- by 

4- by 8-ft unit was defined. Allen M. Brackley, who previously served as a licensed 

wood scaler in Maine and has more than 50 years of scaling experience, notes that 

some mills considered the 4- by 4- by 8-ft section to be part of a continuous pile 

of infinite length and height. Thus, the end marks that defined the 8-ft distances in 

fact sliced individual 4-ft pieces into separate 4- by 4- by 8-ft units. In a similar 

manner, if the wood was on a truck or railcar and piled between stakes spaced 8 ft 

apart so that all sticks were against the stakes, scalers were instructed to adjust the 

width to reflect the edge effect. Height measurements were adjusted to reflect the 

void created by measuring heights to the top of the round stick. Thus, the boundary 

conditions between a cord of wood and its surroundings (whether air, the walls of a 

truck of railcar, or more wood) can influence the actual amount of wood within the 

standard volume.

In the trade of the mid 20th century, the two concepts were referred to as the 

“continuous cord” and the “racked cord.” The racked cord, depending upon many 

other factors, tended to have a solid cubic content of 80 ft3, and the continuous cord 

tended to have a solid cubic content in excess of 85 ft3 per cord. The 80 and 85 ft3

of solid wood in a cord is only a portion of the material that is available for fuel 

use. These cubic contents must be increased 10 percent or more to account for bark. 

The amount of bark is a function of many factors including species characteristics, 

handling, and drying methods.

In the mid to late 20th century, many factors prompted pulp mills and fuelwood 

vendors to convert to weight-based scaling. Many mills making this conversion 

assumed that wood entering the mill over a certified scale was “fresh cut” or 

“green.” The resulting weight factors were a function of the original stick scaling 

methods applied to the material, the amount of drying that took place between 

harvest and delivery, and the species.
22

GENERAL TECHNICAL REPORT PNW-GTR-924

Miles and Smith (2009) reviewed and published sources and collected specific 

gravity estimates from green volume and oven-dry weight. Using this information, they evaluated oven-dry and green weight for 156 North American species. 

It is noted that the green weights they obtained were not necessarily from freshcut material. 

Thus there can be considerable variation in both the cordwood resource and the 

measurement methods. In Alaska, consistent and repeatable cordwood measurement methods will be needed, even if they are adopted on site-specific or speciesspecific basis. 
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