The 17.7 million tons of carbon is a rough estimate based on 10 million wood stoves in operation today in the US. We use the estimate of an average of 1.9 cords of wood being used in each wood stove, based on national studies. For the estimated 3 million EPA certified stoves, we calculated that 1.9 cords of wood would reduce carbon from fossil fuel heating sources by an average of 1.9 tons per year. For the six million older, uncertified stoves, we calculated that those stoves would only reduce carbon from fossil fuel heat sources by an average of 1.5 tons based on the lower efficiency of those stoves. For pellet stoves, we used 3 tons of pellets as the average amount for the 1 million pellet stoves in operation today. We calculated that they reduced 3 tons of fossil fuel carbon. We did not attempt to calculate how much fossil fuel usage indoor and outdoor wood and pellet boilers avoid, but it is safe to say the annual total would likely be over 20 million tons.
We also did not subtract any carbon released by stoves because we believe that cordwood for residential heat is an extremely low carbon fuel. Cordwood is typically gathered or harvested from trees that are already dead and/or down, or from incredibly local, small-scale harvest. A small percentage of cordwood is from larger scale, commercial harvesting which is likely to have a slightly higher carbon footprint. Those larger commercial operations are likely to be geared to the kiln-dried, small bundle market that is more for fireplaces, and not for wood stoves.
The table below shows our calculations and a comparison with residential solar panels.