Hey Mr. Green,
I burn wood to heat my home. Otherwise, I use electric heat when I’m away from home. How can I determine my carbon footprint using the wood versus using electricity?
--Dot in Central New York
The comparative size of your carbon footprint depends on the source of your electric power and the quality of your wood burner. If the electric power used to heat your home is generated from coal or other fossil fuels, then your footprint might be bigger than if you're burning wood in a new, efficient, EPA-approved firebox or stove. But if you've got an old, inefficient stove or a traditional fireplace, your footprint could be way bigger than with electric heat. Also remember that you’ve got a major environmental tradeoff here: Even if the new wood burner has a smaller carbon footprint, per unit of energy it still releases a lot more other pollutants into the air than a coal-burning power plant, and it releases them right where you and your neighbors breathe. Burning wood to heat a home emits 250 times as much global-warming methane as burning coal in a power plant.
Electric heating is not such a great choice either. This is because only around 35 percent of the energy in coal gets converted to electricity; the rest is lost as heat, friction, turning the dynamo, and so on.
To calculate the difference between your two sources, you need to think in terms of British thermal units (Btus) and kilowatt-hours (kWh). Really, it's not hard. Bear with me. Since a typical generator's efficiency is only 35 percent, producing one Btu worth of electricity requires about 3 times as many Btus worth of coal to get the same amount of heat from electricity that you’d get from direct combustion of the coal. Since the carbon emissions generated to produce a Btu from burning wood are only a bit less than burning coal, to get 1 Btu from your wood, the total carbon dioxide released from the stove is roughly half that of coal-sourced electric power, provided you had a modern 75 percent-efficient wood stove. But if you've got an ancient stove, or an old-fashioned fireplace, which can be less than 15 percent efficient, then your carbon footprint could zoom up two or three times higher than with electric heat.
Of course, it’s not as easy to regulate the heat in a wood burner as in an electric heater, so you could end up burning more wood than you really need, pushing your carbon footprint up.
Yes, I know, some optimists will object that burning wood actually has no carbon footprint because wood is a "biofuel" and a "renewable" resource, and trees that replace the tree cut for firewood will absorb the global-warming carbon dioxide given off when wood is burned. This is true in the long run, but if we're serious about global warming, there is no long run, as I've already demonstrated here. The reasoning is simple: Even one of the fastest-growing, quickest-sequestering trees that sprouts up today would require 50 years or more to absorb the carbon emitted by burning a single cord (128 cubic feet) of wood (about the amount in a foot-thick 40-foot-long log). With slower growers, we’re talking a century or so. The twin morals of this story are: 1) Be sure to turn your heat down to 55 or lower when you’re out of the house or asleep, and 2) Beware of exaggerated promises about carbon offsets.