By Adam Flett and Mike Reichenbach
Firewood is used for home heating, camping, cooking or enjoyment throughout the year. Whether you cut, split and stack the wood yourself or buy wood, this article and the accompanying fact sheet on firewood provide information that you may find useful. For example, do you know:
- How much firewood is in a cord?
- The heat value of the wood you are cutting or buying?
- How to reduce the spread of insects and disease?
- How to identify seasoned wood?
- How to store your wood to reduce risk of fire to your home?
A factsheet on firewood from the Minnesota Harvester Handbook can be downloaded here. The Minnesota Harvester Handbook addresses sustainable natural resource harvest and markets. This resource – developed by the University of Minnesota Extension and many contributors – demonstrates the breadth and diversity of natural resources found in and around the state’s woodlands. To purchase a copy go to Minnesota’s Bookstore.
1. How Much Firewood am I Buying?
Purchasing firewood can be hard when terms like cord, face cord, rick, stove cord, and pick-up load all specify quantities of wood. A cord of wood is considered a pile of logs which is 4 feet deep, 4 feet high and 8 feet long. This is equal to 128 cubic feet of wood, bark and air.
Minnesota statutes provide some guidance for use of these terms. The 2014 statutes 239.33 for standard measurements of wood state, “In all contracts for sale of wood the term “cord” shall mean 128 cubic feet of wood, bark, and air, if cut in four-foot lengths;” “If the sale is of “sawed wood,” a cord shall mean 110 cubic feet when ranked, or 160 cubic feet when thrown irregularly or loosely;” “If the sale is of “sawed and split wood,” a cord shall mean 120 cubic feet, when ranked, and 175 cubic feet when thrown irregularly and loosely.”
Ranked means stacked and thrown irregularly and loosely means into a truck for delivery.
2. What is the heat value of the wood you are buying?
A BTU, or British thermal unit, is a unit of measurement describing the amount of heat value a particular substance contains. It is defined as the amount of heat energy necessary to raise one pound of water one degree Fahrenheit. BTU’s can vary greatly between different fuel sources, including differing species of firewood.
BTU capacity varies greatly from species to species; dense hardwoods tend to have the highest BTU values, followed by softer hardwoods and harder softwoods, then lighter softwoods. Hardwood trees are angiosperms or flowering trees such as oaks, maple, and birches, whereas softwood trees are gymnosperms or coniferous trees like pines, firs, and spruces. Firewood enthusiasts prefer the slower, longer lasting burn of good hardwoods rather than the quick burning, high heat intensity of softwoods. If you are looking to warm up quickly, softwoods are ideal, otherwise their use as fuel is usually limited to kindling. Follow this link to learn more about relative BTU capacity: http://mb-soft.com/juca/print/firewood.html
3. Can Firewood Spread Disease and Insects?
Yes. Many states have regulations pertaining to the transportation of invasive species. Many of these species inhabit firewood. You can help by purchasing and using firewood locally or using wood that is certified by the Minnesota Department of Agriculture. There are quarantines in place in Minnesota that prohibit the movement of hardwood firewood. The term hardwood refers to the difference between conifers and broadleafed trees. Conifers are softwood and broadleafed trees are hardwoods. This term does not describe the density or hardness of the wood. For up to date information on the quarantines visit http://gis.mda.state.mn.us/eab/. The DNR urges people to not move firewood. Quoting from the Don’t Move Firewood Brochure:
The only hardwood firewood that can be moved out of quarantined counties is wood certified by the Minnesota Department of Agriculture (MDA) or the United States Department of Agriculture (USDA). All certified wood will have the MDA Certification Shield or USDA Certification Shield on the label. Certified wood has been processed or treated according to the standards required to mitigate plant pest risk before crossing quarantine boundaries. Moving uncertified hardwood firewood out of a quarantine is punishable up to a $7,500 fine per violation per day. MDA and USDA Certified firewood is not the same as DNR Approved firewood. DNR approved firewood is wood available from local vendors and sold at State campgrounds.
DNR approved wood should not be moved from the location where it is purchased.
4. Things to look for in Firewood: Is it seasoned?
Choose wood that has been thoroughly seasoned. In general, firewood is “seasoned” following a harvest anywhere from three months to a year pending the seasoning conditions. Wood that is “green” or unseasoned contains higher amounts of water and makes for a poor fuel. Furthermore, burning wet wood can lead to higher rates of creosote condensation in your chimney, which can lead to increased chances of chimney fires. Signs of seasoning include a relatively lighter weight and cracks or “checks” in the ends of logs.
5. Stacking and Storing
Stacking wood can help save time and space if done properly. Wood should be stored raised off the ground. Raising the firewood can aid in seasoning by providing airflow. Do not place firewood for long term storage in or near your home. Carpenter ants and other pests may move from your woodpile your structure, causing damage or creating a nuisance.
Stacking and storing wood close to your home can also increase your susceptibility to fires. The Department of Natural Resource’s Firewise program is focused on the protection of your home from fire. Creating a defensible space is one of the first steps you can take to reduce your risk for fire; move your firewood pile far enough away from your home or other structures to ensure that if a spark does reach your woodpile, your home will not be in direct danger of catching as well.
Adam Flett is the Stewardship Coordinator at Friends of the Mississippi River (FMR). FMR works to protect, enhance and restore the Mississippi River and its communities in the Twin Cities area, and provides individuals opportunities to contribute to habitat restoration, legislative action, and River stewardship.
Mike Reichenbach is an Extension Educator with University of Minnesota Extension.