Wood burning stoves have a place in history as well as the present. But changing social attitudes about healthy air as well as the governmental regulations that have accompanied them mean that the wood burning stove today isn’t the same as yesteryear. In some nations, use of wood burning stoves as well as fireplaces are severely restricted. In California, the regulations vary according to county constraints or regulations imposed by the local Air Quality Management District. In the Bay Area, as an instance, only wood burning stoves that meet the Environmental Protection Agency (EPA) Phase II regulations could be legally installed or sold. Additionally, visible smoke emissions must be kept to a specified minimum standard, and even the timber commercially available to use in wood burning stoves or fireplaces must be seasoned and never to exceed that a moisture content of 20 percent.
Old-School Wood Burners
Wood burning stoves fabricated prior to the first round of EPA regulations took effect in 1988 are inefficient and discharge unhealthy levels of airborne particulates and toxic gases into outside air as well as the interior of the home. From a health standpoint, many of the long-term consequences of exposure to the release from a pre-1988 wood burning stove would be like those resulting from breathing second-hand cigarette smoke. If you are within a home heated by a wood burning stove and you can smell the wood smoke, you are being exposed to those health hazards. Since these old wood stoves burn wood more rapidly, they also use more fuel, cost more to work and create more residual by-products from the chimney and stove, like flammable creosote, which is a fire hazard.
The New Generation of Stoves
Newer wood burning stoves must comply with the EPA Phase II regulations which strictly limit emissions. Today, the EPA mandatory smoke emission limit is 7.5 grams of smoke per hour for noncatalytic stoves and 4.1 grams per hour for catalytic stoves. New technology in wood burning stoves has created these emission targets very accessible — several models have smoke emission levels as low as 1 gram per hour, and many burn seven times cleaner than old stoves. Consumers comparison-shopping to get a new wood burning stove might assess the EPA White Label affixed to your cooker for emissions specifications for that model.
Noncatalytic wood burning stoves would be the less expensive and much more widely-used models. These stoves incorporate several features to raise the efficiency of combustion and limit emissions. These include enhanced firebox insulation, a system to present preheated combustion air to the chamber and an expanded baffle to expand the gas pathway, resulting in more complete combustion of gaseous emissions. Some parts of a noncatalytic cooker, particularly the baffle, can degenerate over time because of exposure to high temperatures and require replacing.
Catalytic wood burning stoves are the most efficient and produce the least emissions. These units include a ceramic catalytic combustor coated with a rare-metal catalyst to combust gaseous components of smoke as well as airborne particulates, reducing emissions to a minimum. Catalytic stoves burn wood very slowly and create the best heat electricity output from a specified quantity of fuel. Earlier generations of catalytic wood-burners necessitated replacement of the catalytic combustor, sometimes in as few as two years, since the catalyst dropped effectiveness with time. But improvements in the technology have resulted in catalyst systems that last six to eight seasons with only nominal growth in emissions before replacement is needed.
Great Wood Practices
The California Air Resources Board (CARB) advocates specific wood burning techniques for greatest efficiency and decreased emissions from wood burning stoves. Softwood kindling like pine or fir is preferred for starting the fire because it ignites burns and fast warm, bringing the firebox up to temperature quickly. For the main passion, hardwoods like cherry and oak are dense forests that burn long and create less smoke, while delivering more heat energy than softwoods. All firewood of any sort should be “seasoned” — dried out, rather in a sheltered place — for at least six months following splitting. Some hardwoods may require as much as a year of seasoning before they are appropriate for burning. For use at a wood burning stove, CARB recommends wood that’s been dried to a moisture content of 20 percent or less by weight.