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Energy Sources  >  Wood Wednesday, April 23, 2014
 
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Before the 20th century, 90% of homed in North America used wood for heat. During the 1900’s wood heat was almost entirely displaced by the use of fossil fuels. During the 1970’s, wood heating made a resurgence with the introduction of many more efficient wood stoves. Since that time, wood stoves have become increasingly efficient, with the new EPA-certified models reaching 80% efficiency.

There aren’t a lot of good quality statistics on the use of wood for heat in North America because so much of the industry is largely unregulated. Most people that heat with wood either cut their own or buy from a local woodlot. A Canadian study indicates that approximately 43% of rural homes burn wood, although there is no statistic as to how many of those homes use wood as a primary heating fuel. The figure for urban homes is much lower, at 19%.

There is a lot of debate regarding whether we should consider the use of wood for heating fuel as a “green” practice. The arguments against considering wood a green fuel include:
  • Wood-burning appliances and fireplaces may emit large quantities of air pollutants. Wood smoke contains hundreds of chemical compounds including nitrogen oxides, carbon monoxide, organic gases, and particulate matter, many of which have adverse health effects.
  • In many urban and rural areas, smoke from wood burning is a major contributor to air pollution. Because of this, some municipalities restrict wood heating appliance use when the local air quality reaches unacceptable levels.
  • Even the very cleanest-burning and best-maintained wood or pellet stoves release a much higher level of emissions than a typical oil furnace, a common heating fuel in the Northeastern U. S. Natural gas, the most popular heating fuel nationwide, burns even cleaner than oil.
 
  
 
 
 
 
The argument for considering wood as a “green” fuel follows this logic. When oil, gas and coal are burned, the carbon they contain (which was absorbed from the atmosphere by plants millions of years ago) is oxidized to CO2. In effect, the combustion of fossil fuels releases ancient carbon, thereby increasing the atmospheric concentration CO2.

Wood is about half carbon by weight but its use as a fuel is almost carbon dioxide neutral because trees absorb CO2 as they grow. When trees die in the forest and decompose there, the same amount of CO2 is emitted as would be released if they were burned for heat. In other words, decomposition (rot) is a slow form of oxidation whereas combustion in a wood stove or furnace is fast oxidation, with heat as a by-product. When considered over the normal forest regeneration period of about fifty years, heating with wood can be considered almost CO2 neutral.

In addition, the new wood burning technology found in EPA certified stoves cut wood smoke by up to ninety percent compared to older so-called ‘airtight’ stoves. The other main argument in favour is cost. In many cases, the fuel source is free or less expensive than the next cheapest alternative.

There are nuances to both the pro and con arguments, such that some experts are terming the burning of wood to be 75% CO2 neutral. What both sides agree on, however, is that if you are going to burn wood, you should follow these practices to minimize the environmental impact:
  • Use a properly installed and vented EPA-certified wood stove.
  • Season wood outdoors through the summer and for at least six months. Properly seasoned wood is darker, has cracks in the end grain and sounds hollow when smacked against another piece of wood.
  • Store wood outdoors, stacked neatly off the ground with the top covered.
  • Use clean newspaper and dry kindling to start fires.
  • Have the wood stove cleaned and inspected annually.
  • Don't burn household trash or cardboard. Plastics and colored inks on magazines, boxes, and wrappers give off toxic chemicals when burned.
  • Never burn coated, painted, or pressure-treated wood, as it also releases toxic chemicals.
  • Never burn ocean driftwood, plywood, particle board or any wood with glue on or in it. They all release harmful chemicals when burned.
  • Never burn wet, rotted, diseased or moldy wood.
 
  
 
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