Dana Wilde: An inconvenient truth about firewood

One backyard chore I love on these gorgeous September afternoons is moving firewood from one place to another. Flannel shirt, work gloves, west-angling sunlight and 7-foot sunflowers looming over every step. Maple, birch and beech by the armload from the dry stash in the garage and into the basement. Cherry, apple, ash by wheelbarrow from the piles cut and split by Paul and Rick last month and into the garage for next year. —

In the flickering wander of my mind, I sometimes start congratulating myself on how woodburning reduces my use of fossil fuel, aka oil. Meaning that from November to March, or so the thinking goes, we put less carbon dioxide into the atmosphere.

A responsible thing to do, given the situation. Humans push about 40 billion tons of CO2 into the atmosphere every year. “The extra heat that we trap near the planet because of the carbon dioxide we’ve spewed is equivalent to the heat from 400,000 Hiroshima-sized bombs every day, or four each second,” Bill McKibben says in his book “Falter.“ Maybe by burning wood, a local, renewable energy source, I’m lessening by my own few grains of CO2 the human activity that is literally killing Earth.

Or maybe not. Awhile back I decided to fact-check my assumption. My wood stove, it turns out, throws more CO2 and more dangerous particulate matter into the atmosphere than my oil burner.

Heating oil, according to the U.S. Energy Information Administration, produces about 161 pounds of CO2 per million Btu’s. Wood with a moisture content of zero produces about 253 pounds of CO2 per million Btu’s.

No firewood has zero moisture content. The more moisture there is in the wood, the more heat is required to vaporize it, and the more carbon is released. So for example, wood with a moisture content of 50% generates 298 pounds of CO2. The common wisdom is that firewood is ”dry” three months after it was cut; but in reality, it takes up to a year of drying to get the moisture content below 20%, when the wood will burn cleanest.

One cord of red maple dried to 20% moisture content generates about 18.7 million Btu’s of heat. So if you burn, say, 2 cords of dry red maple this winter, you’ll put between about 9,000 and 10,000 pounds of CO2 into the atmosphere.

Wait a minute, you say. There’s no way 2 cords of firewood weigh 10,000 pounds. You’re right. A cord of dry maple weighs less than 4,000 pounds. But the burning wood emits carbon, and the carbon then bonds with oxygen, creating molecules that are heavier than the molecules in the original stick of wood. So the weight of the resulting CO2 is approaching half again as much as the weight of the original wood.

Burning wood also generates fine particles and toxic chemicals, such as formaldehyde and benzene, which can and do cause serious illnesses. What amounts of particles and chemicals go into the air depend on how dry your wood is, the efficiency of your woodstove, and the temperature of your fire (hotter is cleaner). (Also, hardwoods such as ironwood, apple, oaks, ashes, sugar maple and yellow birch burn somewhat cleaner than red maple.) According to the EPA, a certifiably efficient stove burning fairly dry wood generates at most 4.5 grams of particulate matter per hour. An older study showed that a pellet stove generates about 2 or 3 grams per hour, and an oil furnace, about 0.02 grams per hour.

Burning wood also generates fine particles and toxic chemicals, such as formaldehyde and benzene, which can and do cause serious illnesses. What amounts of particles and chemicals go into the air depend on how dry your wood is, the efficiency of your woodstove, and the temperature of your fire (hotter is cleaner). (Also, hardwoods such as ironwood, apple, oaks, ashes, sugar maple and yellow birch burn somewhat cleaner than red maple.) But, according to one study, a certifiably efficient stove burning fairly dry wood generates about 8 grams of particulate matter per hour; a pellet stove, about 2 or 3 grams per hour; an oil furnace, about 0.02 grams per hour.

But at least the energy from firewood is renewable, right? Yes, right. And so Europe in recent decades began generating a lot of its electricity with wood-burning facilities. Two problems, however, arose with this.

One is, the wood is only renewable if you’re renewing it. It turns out that in some places forests are being decimated to supply electricity-generating facilities with wood to burn, and few or no trees are being planted to replace the harvested trees. So not only is the burning wood emitting carbon, but fewer live trees are absorbing CO2 from the air. In the long run, more CO2 is going into the atmosphere from burning the wood than would have from just burning oil or coal.

If you’re getting your firewood from your own property or other woodlots where the forestry practices are growing more trees than you’re cutting, then your heating strategy is generating less CO2 than using oil or coal – in the long run. But this is the second problem: Carbon dioxide levels worldwide are now so high that they’re already disrupting the climate. They have to be reduced, not over the decades your renewing woodlot takes to offset your woodstove’s carbon emissions, but right now.

The critical question for everyone who cares whether life on Earth survives is: How can I reduce the amount of carbon dioxide I’m pumping into the atmosphere?

One answer is to use, if you can, less wood and oil and more electricity. In 2018, about one-third of Maine’s electricity was generated by hydropower; about one-fifth from wind turbines; one-fifth from wood and wood waste burning; about one-fifth from natural gas; and less than 5% from oil, coal and solar combined, according to EIA. The second, better answer is for everybody to use solar-generated electricity. At the moment, however, the cost of the equipment is prohibitive for most of us. Until we get help from our politicians, we have to lean in through whatever small means we have. Burn less wood, if you can.

I’m pretty sure I’m going to get lambasted for saying this out loud. People who like their traditional autumn-scented wood fires as much as I like moving the logs around will find it uncomfortable. When Berkeley, California, called temporary bans on wood burning during the 2014 drought, good citizens of all political bents complained vociferously in defense of their right to their cozy fires.

We keep wanting all the rights, but none of the responsibilities.

And what about Paul and Rick, who most likely are not going to have any work in my woods next summer? Too bad they can’t get jobs as solar-power technicians. But Republican leaders have gone out of their way in recent years to squelch the solar industry.

This week, Gov. Mills told the U.N. that Maine is committed to being carbon-neutral by 2045. We are all in this together. The inconvenient truth is that if there are steps you can take to cut back wood and oil burning at your house, you need to take them. None of us is going to get out of this for free.

And our kids, grandkids and great-grandkids are already in line to pay the heaviest price. We need to reduce it for them every little bit we can.

This column has been updated to correct recent EPA studies showing that a certifiably efficient stove burning fairly dry wood generates at most 4.5 grams of particulate matter per hour.

Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His recent book is “Summer to Fall: Notes and Numina from the Maine Woods” available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.