In defense of wood heat
Why not burn trees where they'll do some good -- in your woodstove?
On these sunny but not hot October days, it's almost a pleasure to toil in the woodpile in my back yard. My firewood is delivered to me bucked (cut to 16-inch stove length), but I still need to split it and stack it.
Even in moderation, this work can lead to an aching back and sore muscles. But it holds out the pleasant prospect of winter evenings next to the cast-iron airtight Vermont Castings Resolute stove in the living room. The wind can howl, the snow can drift, the thermometer can plunge, the electric power even go out -- and I can still be drowsily sprawled near the stove, as comfortable as the two house cats that doze nearby.
Surely that future comfort is worth some soreness now. But it’s not the only reason I feel good about the process. My wood comes from a local building contractor who has a small sawmill, so I'm generally burning scraps that would otherwise go to waste. He cuts it in nearby forests, so I'm not relying on some immense global transportation network.
Nor is my household warmth coming from the natural gas drilling that trashes rural landscapes and injects fracking chemicals into aquifers. (Up to a point, anyway; we do have a gas furnace, kitchen stove, and water heater, though we try to minimize their use.)
As for the carbon that people worry about so much these days, this wood is a product of the current carbon cycle. Burning a fossil fuel, like coal or natural gas, puts carbon (in the form of carbon dioxide) into the atmosphere that had been sequestered. Burning wood just moves around the carbon that was already in circulation –– metabolized by trees 30 or 40 years ago, released on combustion to be metabolized again by other trees.
So why not feel virtuous about the stacks of split ponderosa, aspen and lodgepole? (My wood guy, alas, keeps the good stuff — the piñon pine and scrub oak –– for his own use.) I'm keeping money at home, I'm not supporting some greedy multinational energy complex, and I'm using a sustainable resource, not a diminishing fossil fuel.
But it's more complicated than that. My wood supplier uses gasoline to power his wood-hauling trucks and his wood-slicing chainsaws. His sawmill, and my little wood-splitter, runs on electricity that may come from burning coal.
In fact, unless you're using horses and hand tools on your own back-forty woodlot, there's a certain amount of fossil fuel consumption built into every cord of firewood.
Then there's the annoying fact that wood is a dirty fuel, especially compared to natural gas. The latter is a mixture of two hydrocarbons, ethane and methane. When combined with oxygen, they produce some light and heat; if combustion is thorough, the emissions consist only of carbon dioxide and water vapor.
And with natural gas, as with other fluid fuels like gasoline and kerosene, it's easier to get complete combustion because you can control both the fuel supply (by adjusting the feed valve) and the oxygen supply.
With a traditional wood stove, you can't really meter the flow of wood into the firebox. You've got a bunch of it in there, in varying degrees of combustion. All you can control with any precision is the air supply with the intake on your airtight stove.
Wood is much more complicated than those simple fluid hydrocarbons. The solid part is mostly cellulose and lignin, complex organic compounds, along with some incombustible mineral matter (the stuff that turns into the ash you remove when cleaning the stove). There are also liquids like the water which must be boiled off before the wood can burn, and of course the sap, which varies by plant species but can contain turpentine, resin, gum, and tannic acid.
These materials burn at different intensities and temperatures. If the fire isn't hot enough, the sap liquids evaporate but do not burn. They start up the chimney, then condense against the cooler walls near the top -- forming the "creosote" that can someday fuel a devastating chimney fire if you don't get it cleaned by a chimney sweep. If the vapors escape from the chimney, they can form a haze, along with small particulate matter that can cause respiratory problems.
In general, the hotter the fire, the more completely wood burns and the less pollution it produces. But generally, once we have the fire going, we damp it down to a comfortable level, and thus pollute more. The newer EPA-approved stoves, with their catalytic converters, reduce pollution by encouraging the combustion of the sap compounds.
Even at that, there are mountain towns that have banned wood-burning stoves on air-quality grounds. I can understand that, even if I wouldn't like living in a place where I couldn't have a fire in the winter.
Besides, I think I could develop another argument in wood's favor. Sooner or later, all forests burn; wildfires are part of the natural cycle of things. And forest fires do not practice clean combustion -- they throw plenty of soot, ash and sundry volatile organic compounds into the air.
So if the wood is likely to burn anyway, causing air pollution, why not burn it where and when it will do at least some folks some good? We're going to get the pollution no matter what. It's just a question of whether it comes from our chimneys in the winter or from a ridge west of town on a dry and windy summer afternoon.