Information | |
Wood
Fuel |
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If
unpredictable fossil fuel costs are making you consider turning to wood fuel,
you are not alone.
Throughout the nation, an increasing number of homes use wood either to supplement
or supply all their heating needs.
Until the early 1900’s, wood provided up to 90 percent of our country’s energy.
As coal, oil and natural gas became available, our reliance on wood as a fuel
declined, to less than 1 percent by 1970. After the 1973 oil embargo crisis,
and as the increasingly high cost of fossil fuels began straining budgets,
more and more people returned to wood for home heating needs. In 1982, the
Department of Energy estimated that wood fuel provides about 5.5 percent of
our energy needs, of which about 2 percent is used in home heating.
While wood has become a popular alternative home fuel, it will not totally
replace oil, coal and natural gas in the foreseeable future. It can, however,
complement the energy mix and make our country less dependent on expensive
and increasingly scarce fuels.
Wood is a form of solar energy. Sunlight, through photosynthesis, turns carbon
dioxide and water into organic material. When wood is burned in an efficient
stove it produces heat, carbon dioxide, water vapor and ashes. These are commonly
called the products of complete combustion. Unfortunately, the burning
process is seldom efficient. Most wood heating appliances produce substantial
amoun ts of smoke (unburned organic compounds) and carbon monoxide in addition
to the products of complete combustion. Smoke and carbon monoxide are potentially
hazardous to human health.
Wood is a renewable source of energy. Commercially undesirable trees can be
used for firewood, making space for new growth. As long as the forest is properly
managed, and only the amount of wood that can be replaced is taken, little
or no significant environmental damage occurs. By encouraging new growth,
a greater diversity of wildlife habitats generally develops.
How Much Wood?
Obtaining quality wood is not always simple. Either you buy from a dealer that you believe to be trustworthy or you resort to trial and error. In many areas you can even cut your own wood. Let’s assume that you would prefer not to “get burned” before the wood gets into your stove and begin your education here. You have five considerations when buying wood: the amount of wood, the species, the moisture content, the degree of preparation, and finally, the price.
Standard Cord
Wood is sold by standard units of measurement. A standard or full cord has
a volume of 128 cubic feet, measured in a pile as 8 feet long, 4 feet high,
and 4 feet wide. There are really only about 80-90 cubic feet of wood in most
cords; the rest is air space. A full cord weighs about 3,000 pounds when
dry or can be over two tons when wet. One should check all deliveries to make
sure you have received a reasonably honest cord measurement.
Face Or Short Cord
A face cord is a pile of wood 8 feet long, 4 feet high, and as wide as the
lengths of the wood cut, usually 12, 16 or 24 inches. A face cord is less
than a full cord and should be priced less. A face cord of 24-inch logs is
half the volume of a full cord, a 16-inch face cord is one- third the volume,
and a 12-inch face cord is only one-fourth the volume.
A “truck load” is a vague description of an amount of wood because the amount
depends on the size of the dealer’s truck. A standard pick up bed will only
hold one-third to one-half of a full cord. Beware of what the dealer claims
to be “about” a cord, delivered in a half- ton pickup truck! The amount can
also vary from 10-15 percent by the way wood is stacked. If you have doubts
about a cord’s real volume, stack the wood before you pay. You should expect
small variations in the size of wood piles. A dealer usually measures and
stacks the wood in the forest, and once it is split and restacked, it may
pack into slightly less volume. Also, if you buy green wood, expect it to
shrink about 8 percent in volume during seasoning.
Most dealers are local people who have a reputation to protect and will correct
substantial shortages. It is, however, illegal to deliver less wood than is
advertised and paid for. Your state’s Consumer Protection Agency enforces
laws that offer some protection against habitually unscrupulous dealers. Call
them if you think you have been cheated.
Heat Value Per cord (In BTU Per Coed)1 |
||
High 24-31 |
Medium 20-24 |
Low 16-20 |
Live Oak |
Holly |
Black spruce |
Shagbark hickory |
Pond pine |
Hemlock |
Black locust |
Nut pine |
Catalpa |
Dogwood |
Loblolly pine |
Red sider |
Slash pine |
Tamarack |
Tulip poplar |
Hop hornbean |
Shortleaf pine |
Red fir |
Persimmon |
Western larch |
Sitka spruce |
Shadbush |
Juniper |
Black willow |
Apple |
Paper birch |
Large-tooth aspen |
White oak |
Red maple |
Butternut |
Honey locust |
Cherry |
Ponderosa pine |
Black birch |
American elm |
Noble fir |
Yew |
Black gum |
Redwood |
Blue beech |
Sycamore |
Quaking aspen |
Red oak |
Gray birch |
Sugar pine |
Rock elm |
Douglas fir |
White pine |
Sugar maple |
Pitch pine |
Balsam fir |
American beech |
Sassafras |
Cottonwood |
Yellow birch |
Magnolia |
Basswood |
Longleaf pine |
Red cedar |
Western red cedar |
White ash |
Norway pine |
Balsam poplar |
Oregon ash |
Bald cypress |
White spruce |
Black walnut |
Chestnut |
|
| 1) Assume 80 cubic feet of solid wood per cord and 8600 BTU/lb. of oven dry wood. | ||
Wood Chips and Pellets
An alternative to fueling a furnace with wood logs is to use wood chips
and pellets.
Wood chips are produced when chipper machines are fed with otherwise unused parts
of a tree, such as limbs and wood pieces. Pellets are a manufactured, compressed
fuel made from sawdust, bark, cardboard, peat, wood, and/or other wood byproducts.
Both chips and pellets have advantages over cordwood; they are easier to haul
and store, can be moved by automatic systems, and can be composed of wastewood
or harvest residues. Their main disadvantage is that they require special
stoves and furnaces with automatic stokers. Pellets may also be difficult
to obtain in some areas because there are currently less than 50 pellet preparation
plants in the
You can produce your own wood chips, but it is rarely cost-effective. Though
you might have a group-sharing plan, buying your own
chipper would be a sizable investment, costing from $4,000-$20,000.
Pellets and wood chips also have differences. Pellets are more uniform in
size, have better flow characteristics and a higher energy density when compared
to chips. Pellets also have a lower moisture content
and thus produce less creosote and pollution. Pellet, however, have to be manufactured, and are therefore less
accessible. While chips are generally less expensive than pellets, in some
areas they are priced higher due to demand from paper mills.
Storage
Wood storage methods affect how efficiently your wood burns. First and foremost,
wood should be kept dry or stored so it can season.
It is best kept outdoors and under a plastic cover or roof, protecting it
from the rain, snow and ice. Keep an air space between the wood and cover.
This promotes better air circulation and accelerates drying.
The wood can either be stacked between braces or between trees. Stack it on
concrete slabs or otherwise raised off the ground
to better allow air to circulate underneath. You can also speed up drying
with a solar-enhanced wood dryer. This storage
method consists of an enclosed bin with polyethylene covering the south side
and vents to release moisture. You can build such a bin yourself.
Species
The most important species characteristic is the wood’s heating or Btu value.
Certain species of wood such as oak and maple are denser. When an equal volume
such as a cubic foot of wood is burned, hardwoods, because of their higher
density, tend to burn longer and slower than softwoods. Thus, you don’t have
to restoke as frequently. Buyers should note the wide range of heating values
among the different wood species (see table). One should generally pay 
less
for softwoods and more for hardwoods.
Most wood dealers do not take time to segregate the wood species or grades
of density. It is usually cut and piled as it falls. It is helpful to be able
to recognize firewood by the bark so you can better determine the wood’s value.
However, a cord of hardwood mixed with some softwood, is still a good buy.
Good dry softwood such as pine makes excellent kindling for starting fires
and it also works well as a mixture in the fire box. Softwood burns faster
and hotter while the hardwood lasts longer.
Wood species also vary considerably
in ash content. For example, oak (generally considered a premium wood) has
about 4 percent ash content while pine only has about 1 percent. A home that
burns mostly oak has a lot more ash cleaning and disposal to do.
Wood is usually advertised as green or seasoned. Seasoned wood is preferred
because the moisture content is roughly half that of unseasoned wood. Seasoned
wood provides more heat to the room because heat isn’t wasted in evaporating
moisture from the wood. Seasoned wood also ignites easier.
Wood thoroughly dried in an oven and burned under laboratory conditions yields
a heating value of about 8,600 Btu per pound. Wood does not dry that well
naturally. Actually, wood chemically burns best with about 20% moisture content.
Well seasoned or air-dried wood, protected under cover, still can have a moisture
content of about 25%. At 25 percent moisture level, only four percent of the
energy is lost through evaporation. Green or wet wood has a moisture content
of at least 60 percent, wasting over 15 percent of the wood’s heating value
on evaporation.
“Seasoned” is a vague term, so be sure to ask your wood dealer when the wood
was cut. It should have been stacked and stored at least six months. You may
want to buy your wood in the spring or early summer to allow proper seasoning
before winter. Also, the prices may be lower in this off-season period.
Degree of Preparation
Preparing wood is hard work, consequently the
wood’s price largely depends on how much work you are willing to do yourself.
If you want your firewood split into fine pieces and stacked near your doorstep,
expect pay a premium price. If you want to go the cheapest route, cut the
wood
yourself from standing trees. Wood can be bought in almost any stage between
these extremes. It is common to buy wood in 4- to 16-foot lengths to cut and
split for yourself. Wood delivered in this form usually costs about half that
of wood cut and split. However, cutting and splitting wood involves hard work
and equipment. There are few real “deals” in buying wood, just an exchange
of your sweat for the dealer’s sweat. Other sources of wood ay include scavenging
the local tree dump, picking up windfalls on the roadside, buying cutting
rights from a private landowner (many times done as shares—one cord for you
and one for him), and cutting wood on State and Federal lands under their
permit program. Wood co-ops also can make firewood available at lower costs.
To find out about ways to obtain wood in your are a, you could try watching
newspaper advertisements, asking friends, or calling the local office of your
state forester. The possibilities are endless and only depend on one’s ambition
and resourcefulness.
Price
Prices for the same types of wood vary from place to place according to the
labor cost, transportation costs, supply and demand.
Shop around, try to buy when the
demand is low and be sure you understand what you are buying.
A rule of thumb for comparing the economics of wood fuel versus oil:
hardwood fuel should be no higher (in dollars per cord) than 1 1/2 times the
price of oil (in cents per gallon). For example, wood at $120 per cord equates
with oil at 80 cents per gallon, 65 cents per therm of natural gas and 2.5
cents per kilowatt hour of electricity. However, an accurate comparison must
also consider the specific heating system’s efficiency.
Conservation and Renewable
Energy Inquiry and Referral Service
or call toll-free
800/523-2929 (
Islands and Puerto Rico)
800/462-4983 (
800/233-3071 (
Bibliography
The following publications provide further information
on wood fuel. This list does not cover all the available books, pamphlets,
plans and articles on wood fuel, nor is the mention of any publication to
be considered a recommendation or endorsement. To obtain the publications
in this bibliography, contact your local library, bookstore or the publisher
before placing an order.
Books
. . J.W. Shelton;
The Woodburner’s
Handbook.
G. O’Connor, R. Joly, and C. LeMay; Rural Center for Appropriate Technology,
Algonquin College of Applied Arts and Technology, Plantagenet, Ontario, 1980,
153 pp. A simple method of sizing wood stoves is presented, along with info
rmation on firewood, wood-stove economics, and safe system installation, operation,
and maintenance. A trouble-shooting section reviews common problems associated
with wood heating, sums up probable causes, and gives possible solutions.
Pamphlets
. . . L.D. Baker, et al; Cooperative Extension, Northeast Regional Agricultural
Engineering Service, Riley Robb Hall,
Other
Short; 1982, Department of Energy,
Mines and Resources and
pp., ISBNO-9201 14-41-5.
Wood
Chip Primer. . . Energy Secretariat, Province of New Brunswick, P.O. Box
6000, Fredericton, New Brunswick, Canada E3B 5H1, 1983, 25 pp. In
both French and English. Discussion of a wood chip
burning system and answers questions about wood chip heating.
Plans
Drying Wood with
the Sun: How
to Build a Solar-Heated Firewood
Dryer.
. . Superintendent of
Documents,
Printing Office,
061-000-00613-3.
Articles
How to Mix Wood and Coal. . .
P. Matthews; Rodale’s New Shelter:
4450, September 1980. Discussion
of a multi-fuel system.
Particulate Emissions from Residential Wood Combustion .. Biologue
2(1): 17-18, February/March 1985. Discussion on magnitude of and solutions
to the wood stove pollution problem.
Wood Particle Fuels: Chips are Cheaper, But Pellets Don’t
Pollute…M,E.C. Gery; Renewable Energy News 7(1): 12, April
1984. Discussion of the attributes of wood chips and pellets.