Smart wood burners know by experience how to gauge whether their firewood is dry enough or use a moisture meter. Easy-to-use moisture meters, available locally from The Woodway for $30, can help wood burners raise fuel efficiency while reducing creosote buildup (& chimney fires) reduce woodsmoke pollution.
A FDNM article by Ned Rozell, “Dry wood is good wood” 8/2010, gives information on the importance of drying firewood before burning and how long it takes. Fairbanks fourth grader Linnea Schultz’s science fair project “A burning question: how long should birch firewood be dried?” garnered interest when it was displayed at the Tanana Valley Fair in August. Schultz concluded that birch firewood that had been split and then dried for 16 months had more than 20 percent moisture remaining. She found that split birch dried for 28 months “had a moisture content below 16 percent and was dry enough to burn properly.”
Wood burners can be misinformed by some of the available information on how long firewood needs to be dried. Alaska Department of Environmental Conservation has public educational information on particulate matter “Air Non-Point and Mobile Sources.” Unfortunately, their “Woodstoves” brochure urges “Dry wood a minimum of 3 months; but up to 12 months if possible.” The phrase “up to” makes it sound as though gets too dry if dried for more than a year; but the truth is drier wood makes better firewood. According to Schultz’s study, the only available scientific study on how long firewood needs to be dried in Fairbanks, wood dried for 16 months still had more than 20% moisture.
Responsible wood burners need to be cautious about following conventional recommendations for firewood drying time, as they do not apply in Fairbanks due to our long winter and thus, relatively short drying season. The Environmental Protection Agency’s “Burn Wise: Consumers – Best Burn Practices” publication recommends drying wood “at least 6 months.” That’s better than 3 months, but it’ll still be too wet!
FNSB Air Quality Fairbanks office Burn Wisely information states, “Season at least 6 months (more is better).” The Borough Air Quality Fairbanks also produced a brochure called “Burning Wood Wisely” which refers to the following CCHRC “optimal” drying conditions study.
The Cold Climate Housing Research Center’s “optimal” drying conditions study (unpublished) in 2010 was refered to in this Best Practices Cordwood Handling Brochure from CCHRC [506KB]. CCHRC found it took only 6 weeks to dry the wood to 20% or less moisture content. These conditions appear to have included locating the covered & split “cross-stacked” wood in the sun beside their building, baking in the building’s reflected heat.
Optimal but unrealistic and unsafe. State Farm and the Alaska Division of Forestry in their FireWise program advise homeowners to stack firewood at least 30 ft away from houses or other buildings of value in case of wildfire.
Dry wood with 20% or lower moisture content makes a hotter fire. A hotter fire burns up the smoke particles, called a “secondary burn.” The result of burning hot is higher efficiency (more home heating benefit out of the wood), reduced creosote buildup and thus lowered chimney fire potential, and reduced fine particle pollution (PM 2.5). Plus, the wood is about half its wet weight, making it easier to haul inside. Wasting wood by burning wet takes two or more times as much wood, laying waste to our forests like the Tanana Valley State Forest which is to be managed for sustainable uses.
From BurningCleaner.com: “Smoke, in the form of solid particles (“particulates”) and volatile gases, is unburned fuel. An improperly operated wood stove fails to achieve the high combustion temperatures necessary to burn the particulates and ignite the gases. These gases and particulates contain half the heating potential of your firewood. The loss of this fuel up the chimney amounts to a loss of efficiency. Improperly operated wood stoves can also adversely affect air quality. However, the use of EPA-certified wood stoves and wood burning fireplace inserts, combined with the proper operation of all wood burning stoves and inserts, can decrease the level of polluting emissions by up to 85 percent.”
According to an 1986 USDA study by George Sampson and Anthony Gasbarro, the moisture content of freshly cut Alaskan birch is over 80%.
The Environmental Protection Agency published “Strategies for Reducing Residential Wood Smoke” 2009 to help communities consider a range of strategies to tackle their own woodsmoke pollution problem.
The Woodway has links to videos from the Northwest Hearth, Patio & Barbecue Assn on using firewood safely and efficiently.
The FNSB Air Quality Ordinance, 2010-28, prohibits the burning of wood above 20% moisture content, after 9/1/2011, see page 8. Proposition A appears to negate this requirement for residential heating.