Is burning wood for heat green? In a word, no.

stove with dog
© Agni Hutte

As we learn about the dangers of particulate pollution, it becomes obvious that we have to stop burning wood.

Every couple of years we ask the question: Is burning wood for heat green? We go back and forth; just two years ago I tried to justify its use in a Passivhaus residence, noting that "the source people use for energy is far less important than how much they use." The justification is that in a super-insulated building, if it is just a teensy bit of wood, then it is not such a big deal. As architect Terrell Wong said, "Reducing your need for heating 90%... Then occasionally having a fire in an uber-efficient German boiler is not a bad thing."

fireplace© Stone's Throw Design
But the evidence continues to pile up that small particulates, PM2.5, cause some of our most serious health problems. As Christopher Ingraham noted in the Washington Post, the understanding of the seriousness of particulate pollution is relatively recent:

Researchers and policymakers have only recently begun grappling with the effects of PM2.5 — the Environmental Protection Agency didn't have a separate regulatory standard for it until 1997. PM2.5 particles are tiny — about 1/30th the width of a human hair. Its small size “allows it to remain airborne for long periods, to penetrate buildings, to be inhaled easily, and to reach and accumulate within brain tissue.”

PM.2.5 have long been known to contribute to asthma and COPD, but new research ties it to heart attacks and a New England study tied PM2.5 to brain volume. Ingraham writes about a link to dementia:

“a 1 microgram-per-cubic-meter [μg/m³] increase in average decadal exposure [of PM2.5] increases the probability of receiving a dementia diagnosis by 1.3 percentage points.” That's a stunning figure, particularly given that ambient PM2.5 levels vary by much greater than that on a county-by-county basis.

Other studies link it to autism:

Six studies report links between autism and PM2.5 exposure during pregnancy (mainly the third trimester). The risk of autism was also increased by PM1 exposure in the first 3 years of life in a study in China – an 86% increase for a 4.8 ug/m3 increase (the inter-quartile range, IQR) in PM1. The effect of PM2.5 exposure was similar (79% for an IQR increase of 3.4 ug/m3)

emission from different furnancesPuget Sound Clean Energy Agency/Public Domain

Using a teensy bit of wood doesn't make it OK either; just two and a half days of burning an EPA certified wood stove puts out as much PM2.5 as a car does in a year. Nor does being in the country; some of the worst air quality is found in valleys where people burn wood for heat.

Launceton AustraliaEvaluation of interventions to reduce air pollution from biomass smoke on mortality in Launceston, Australia/via

One study in Tasmania found that banning wood heating "was associated with reductions in all cause, cardiovascular, and respiratory mortality."

Then there is the question of whether those EPA certified stoves actually reduce particulates and other pollution as much as they are rated to. It turns out that if the wood is too wet then emissions are higher. If the wood is too dry, then particulates go way up. It has to be just right, at about 20 percent.

It also matters how old the stove is and how much it is used. According to Doctors + Scientists against Wood Smoke Pollution,

Emissions from both newer non-catalytic and catalytic wood stoves increase over time due to physical degradation of the stoves from use. Within five years the particulate emissions from a catalytic stove may reach the level of an older, uncertified conventional wood stove. According to a report for the US EPA, “Over the normal life of the catalyst, the average performance of the heater will be similar to that of a non-catalyst heater that does not change its emission performance as significantly with time.”

myth bustedEPA NSW/Public Domain

Is it carbon neutral?

The EPA announced last April that it would class the burning of biomass as carbon neutral; then-EPA head Scott Pruitt said:

“Today’s announcement grants America’s foresters much-needed certainty and clarity with respect to the carbon neutrality of forest biomass. Managed forests improve air and water quality, while creating valuable jobs and thousands of products that improve our daily lives.”

A lot of people in the industry claim that burning wood is carbon neutral, but it isn't really. Yes, it is true that when wood is burned, it is releasing carbon that was pulled out of the air and planting a new tree will absorb it again, which takes about 80 years. Meanwhile, when the wood is burned we get a giant carbon burp now. [this has been edited, see comments]

Norwegian woodNorwegian wood bought in the middle of a Canadian forest/ Lloyd Alter/CC BY 1.0

You also do not get to 100 percent recovery, because it takes energy to harvest the wood, they don't get all of it but leave branches and leaves to rot, and it takes more energy to move it to where it is burned. Like any other product, it has become separated from its source; a few years ago I bought a bag of firewood for my cabin at the local hardware store (in the middle of a forest!) and found that it had been shipped all the way from Norway. This is not going to be carbon neutral wood going into my fireplace.

In conclusion...

Interior table© Juraj Mikurcik

A lot of Passivhaus designers like Juraj Mikurcik and Terrell Wong, along with people like Alex Wilson, who knows more about building green than anyone, have used wood stoves for those few days a year when they need a bit of heat. It is certainly more carbon neutral (and a lot prettier) than a jug of propane in an off-grid situation, but I am beginning to wonder if it isn't still a mistake, given the health considerations. It is probably time to conclude that burning wood isn't green, and it isn't safe.

Is burning wood for heat green? In a word, no.
As we learn about the dangers of particulate pollution, it becomes obvious that we have to stop burning wood.

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