Wood for Fuel

The use of firewood in stoves, furnaces and fireplaces is often considered for home heating by homeowners.  Before running out and buying a new wood stove or chain saw, consider some facts about your wood supply and the effort and resource needed to produce it.

Most species of wood contain approximately the same amount of energy per pound, assuming they are at the same moisture content.  Firewood at 20% moisture content or air seasoned for at least one year has approximately 7,000 Btu’s of energy per pound.  Species differences occur in firewood because of the density variation across species.  In Iowa basswood weighs about 25 pounds per cubic foot and shagbark hickory weighs about 51 pounds per cubic foot. Firewood is often measured and sold by the stacked volume.  A cord of wood is a stack of firewood 4” x 4’ x 8’ or 128 cubic feet of wood and air.  A cord of air dried basswood weighs a ton and shagbark hickory weighs two tons; therefore, a cord of shagbark hickory has twice the heat value as a cord of basswood.

Species of Wood Weight per Cord (lbs)
Shagbark Hickory 4072
Basswood 1984
Osage Orange 4792
Red Oak 3536
Green Ash 3296
Silver Maple 2752
Cottonwood 2272

Consider the heat equivalents for home heating.  Assuming that the wood appliance is 60% efficient compared with either LP or natural gas at 85% efficiency or electricity at 100%.  A cord of basswood is equivalent to 9700 cubic feet natural gas, 108 gallons of LP or 2427 kilowatts of electricity; a cord of shagbark hickory is equivalent to 20,000 cubic feet of natural gas, 223 gallons of LP or 4994 kilowatts of electricity.

Firewood must be seasoned or dried.  To accomplish this, requires that the wood be cut and stacked for at least a year before burning.  The average wood usage in Iowa for home heating is 3-7 cords per year.  

Using firewood for home heating requires a good supply of firewood.  A few trees in the backyard is not sufficient.  Most woodlands in Iowa are capable of producing or growing up to a cord of wood per acre per year with good management.  Firewood burners should have a minimum of 5 to 10 acres of a well stocked (land fully occupied with trees) and well managed woodland to provide the fuel for heating the average home.  

 If the homeowner is planning on using wood as an alternative source of energy, consider all aspects of wood burning including the cost of the stove and installation, supply of wood, production cost including equipment such as chainsaw, splitter, and pickup, storage of the wood, planning at least a year ahead of time, and the hassles of feeding and tending the wood burning equipment.

Burning wood can have impacts on the environment through smoke pollution outdoors, indoors and damage to the woodland or forest through unwise practices.  It is safe to say that if wood from a sustainable managed forest is properly processed, dried and burned in a properly installed and maintained efficient wood burner, the environmental impacts will be minimized.

Thinning Woodlands for Firewood Production

The goal of fuelwood harvests should be to make the woodland better after the harvest than before. Concentrate this timber stand improvement practice on young stands (6-10 inches in diameter) because their growth increase will be greater. Thinnings should be done to allow desirable trees more growing space. Care must be exercised in harvesting to ensure that the quality of the woodland is not reduced.

First, identify the "crop trees". Start at any location in the forest stand and on the average of every 20 feet, identify and mark with a non damaging marker such as plasctic or cloth flagging the best trees. The best trees are generally of high value species and trees with the best form and potential to develop into high quality sawlogs when they are mature. 

A species priority list from high to low might include black walnut, red oak, white oak, black oak, bur oak, ash, maple, basswood, and hickory. Crop trees must also have good form; trees that are tall, straight and have a clear trunk should be selected over less desirable forms.  

When working with Iowa woodlands, work with what is in the forest. You will generally mark a variety of tree species, some with excellent form and some with less desirable form, but always the best in that growing space. Crop tree spacing will vary from less than 10 feet to more than 30 feet, but always try to select the best 100 trees per acre. 

After the crop trees have been identified, mark the trees which should be removed for firewood. Work with each individual crop tree and looking at its crown or foliage with respect to its competitors. The goal of thinning is removal of competing trees on 3 to 4 sides of the crop tree if they are crowding or overtopping the crop tree. 

Allow the crop trees some room for expansion or growth, but do remove all competition. If the crowns of competing trees are 3 to 4 feet away from the crop tree, it is not interfering with growth at this time, although as they grow larger, it may have to be removed in future thinnings. Follow this procedure for all crop trees in your stand. 

Over thinning around crop trees may result in reduced quality because of epicormic branches which are formed by buds beneath the bark that begin to grow in response to too much sunlight. Never remove trees if their crowns are below the crowns of the crop trees because they will continue to promote self pruning of the crop trees.

Other Resources: 

Woodland Management

Woodland Improvement and Crop Trees in Iowa