Wood Fuel for Heating - November 17, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County


Fuelwood is a renewable resource and is relatively plentiful in northern Arizona. We have multiple species of juniper and oak, walnut, sycamore, alder, ash, elm, hackberry, box elder, pinyon pine, and ponderosa pine available. Especially plentiful is juniper and removal of densely growing juniper can improve wildlife habitat and plant species diversity. Wood heat, however, does require some considerations: wood must be stored and kept dry and the wood heater must be maintained for efficiency and safety.

Fuelwood has been harvested commercially in northern Arizona since European settlement and has been used to provide residential heat for thousands of years. I am always amazed when I come across a juniper stump out in the middle of nowhere that was cut by an axe. Woodcutters cut and gathered from far and wide to supply energy and timbers for mines in Jerome, Humboldt, Prescott, and Crown King. Much of this activity is barely visible today due to regeneration of cut trees.

Energy contained in wood is usually expressed in British thermal units or Btus. One Btu equals the amount of heat required to raise the temperature of one pound of water one degree F. One pound of very dry (zero moisture content) wood of any species has a calorific value of approximately 8,600 Btu. Any moisture in the wood reduces the recoverable heat by carrying heat up the chimney during vaporization. Each pound of water vaporized uses about 1,200 Btu. This is why we want to burn dry wood in our stoves and fireplaces.

Many fireplaces are inefficient because their open front allows heat to escape up the chimney. Installing glass fire screens with proper draft controls, or "heatilators," can increase fireplace efficiency. Properly designed fireplaces can also decrease heat loss. Modern fireplaces may have metal side walls and backs with space for air to circulate between the walls and the fireplace setting. Inlets near the floor and outlets near the mantel provide convection-air heating and circulation in addition to the radiant heat from the fireplace.

Airtight wood stoves are more efficient. Many of these utilize "down-draft" combustion which forces combustible elements along a circuitous route where they are mixed with a current of hot air and nearly all burned. In less-efficient units these elements escape up the chimney or are deposited in the flue in the form of soot and creosote. Selecting a wood stove/heater is not simple. You must consider safety and space constraints as well as the size of the area to be heated and your personal preferences. In general, a medium or large wood stove can heat 1,000 square feet of living area to most people's satisfaction and up to 2,000 square feet for those having the wood stove ideally located and desiring somewhat lower temperatures.

The species of wood used will often depend on household needs, availability and cost. Oak is generally more expensive than juniper, and juniper is generally more expensive than pine. The price range is about $150 to $250 per cord. One cord is a tightly stacked pile 4 ft x 4 ft x 8 ft. Oak can have between 25 and 36 million Btu/cord (depending on species). Juniper has about 26 million Btu/cord and ponderosa pine has about 22 million Btu/cord. Wood available for purchase should be seasoned for at least one year. Every once in a while you may find other highly desirable hardwoods such as walnut or ash, but be sure to assess any prospective wood for rot.

Another consideration for purchasing wood is whether or not it will be stacked. Stacking wood is good exercise, but may be beyond the physical ability of some people. Firewood should be stacked above ground (I use pallets) and covered with a tarp. Do not stack your wood on or near other flammable materials such as porches and decks. Doing so puts your home at greater risk in the event of a fire. Finally, if you heat with wood, have your chimney inspected and/or cleaned yearly to reduce soot and creosote that can cause a chimney fire.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: November 10, 2010
Content Questions/Comments: jschalau@ag.arizona.edu

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