The Seven Deadly Sins of Wood Heat

The Seven Deadly Sins of Wood Heat

Humankind is living through a period of extreme stress. As the climate crisis barrels ever closer it triggers the fight or flight response (to some degree) in anyone who believes in science. We all need to keep cool heads and open minds in order to get this right. This moment is too important for tribalism and confirmation bias. It is in that spirit that we present this round up of the most common objections to wood heat.

1. We should focus on solar heating and the electrification of everything.

The Home heating carbon footprint opportunity
The Home heating carbon footprint opportunity

New buildings with high-performance envelopes can be heated affordably with heat pumps and auxiliary heat, but the 57 million older homes currently heating with oil will need to be heated utilizing their existing distribution systems. Those systems require  high temperatures that can only be achieved with an appliance that is fired with combustion. In other words we only have three options for heating the majority of America’s existing buildings: oil, gas, or wood.

More than half of America’s 118 million homes and 5.6 million commercial buildings were built before 1980. Maybe one day we will be able to heat our older buildings affordably with electric heat from renewable sources. (see: At What Temperature Will a Heat Pump Become Ineffective?) Unfortunately that technology doesn’t exist now and is not in our immediate future; not even with weatherization and Deep Energy Retrofits (DER.)

Space heating accounts for 60% of home energy use, and hot water is an additional 15%. That makes heating 75% of home energy use for homes in the northern half of the US. In order to achieve our climate stabilization goals we need to address heating pollution. Heating has an environmental cost, full stop. Wood heat is a bridge fuel that offsets fossil fuels while we concurrently work on even better heating technologies, see Sin #5. When we create heating markets for low-grade waste wood it avoids all that methane.

2. Cutting trees for heat devastates forests right at the time we need increased carbon sequestration.

Most US forest land is not protected. There are not enough public and private resources to preserve the rest.

Forest preservation is an incredibly important cause, but so is conservation of working forests. We need both!

Because the financial value of land is always greater as development than as a working forests, Americas forests are at risk for development. For example, Vermont looses forest at the rate of 22 acres per day. This dynamic plays out across the country because of the weak market for US forest products. Working forests are essential to carbon sequestration:

20% of forest harvest is permanently sequestered in our wood buildings and furniture, and building with wood also offsets more carbon-intensive building materials like steel, concrete, and plastic. We need to sequester more carbon by valuing, incentivizing, and creating markets for working forests.

70% of forest harvest is waste wood that cannot be used for building materials or furniture. In New England, we have an incredible abundance of this low-grade waste wood. It used to be used for making paper, but the loss of those markets (think smartphones) makes it more difficult for landowners to maintain their wood lots in current use. The lure of quick profits from converting woodland to development is a real and present danger. Leaving wood to rot on the forest floor releases methane from the anaerobic digestion that occurs as the wood is broken down over time. Methane is many times worse for the atmosphere than CO2.

At a minimum, heating with wood pellets reduces greenhouse gas emissions by ~60% when considering the life-cycle analysis of sourcing, processing, and transporting heating fuels.1

Effective utilization of waste wood drives responsible forest practices. In addition to disincentivizing development, responsible use of low-grade conserves wildlife habitat, water quality, air quality, and view sheds. Using clean-tech wood pellets and chips to heat our homes and businesses is better for the environmnet than oil or gas.

3. Heating with wood is not carbon neutral when factoring for soil disturbance, logging, trucking, etc.

Biogenic carbon Vs. geologic carbon graphic
Biogenic carbon Vs. geologic carbon

It is true that fossil fuels are used in the harvesting, trucking, and pellet manufacturing process. That is called “sunk carbon.” Home heating oil and propane also have sunk carbon from trucking, refining, drilling, fracking, and being shipped across the ocean on tankers.
Supply lines for wood heat are much shorter but the bottom line is that it is pretty impossible to get to a reliable true cost accounting for the full inventory of climate effects for the various heating fuels. The data can be spun many ways, and trying to get at “the truth” most often just leads to confirmation bias and falling back into entrenched positons.

Consider just a few of the top level arguments:

  • It is true that harvesting trees will disturb soils which in turn releases carbon stored in the soil.
  • It is also true that leaving wood to rot on the forest floor releases methane from the anaerobic digestion that occurs as the wood is broken down over time. Methane is many times worse for the atmosphere than CO2.
  • Large quantities of methane are released into the atmosphere during natural gas distribution.
  • And how should we account for the alarming increase in natural gas explosions?
  • And let’s not forget the devastating oil spills including the Exxon Valdez and BP’s Deep Water Horizon. (When a wood pellet truck spills there’s no need to clean up the baby seals.)

The bottom line when it comes to heating most of America’s existing housing stock with a central  furnace is that our only three choices are oil, gas, and wood. Oil and gas release geologic carbon which adds to the total carbon in the earth’s atmosphere. Heating with wood utilizes the earth’s natural biogenic cycle. Could that still play out badly over time? Absolutely! That is why it is so important that we create markets for sustainably sourced low grade waste wood. More than ever we need to pay attention to all aspects of our energy choices.

4. Slow in / fast out. Trees grow and sequester carbon slowly. We can't afford that deficit right now.

Carbon Neutral wood heatThink of a tree as a solar battery. As a tree grows, sunlight, rainfall, and carbon dioxide combine to store the sun’s energy. When it dies, the tree falls to the ground and rots, releasing the same amount of carbon it absorbed during its life.

“The forest product industry rightly claims that trees harvested are replaced with new trees. Obviously, mature trees are harvested and small seedlings are planted in their place. Some environmentalists claim that, while trees do grow back in time, it takes decades for each harvested tree to be replaced. That is a true statement, however, it is an incorrect assessment of what is occurring on a landscape or regional level where there is a continuum of planting, managing, thinning and harvesting taking place. So, what really matters is whether forest inventory is increasing or decreasing in a region. …we are currently growing more volume of trees than is being harvested and, therefore, there is no carbon deficit when viewed at the proper landscape level1.”

Leaving the low-grade waste wood on the forest floor leads to poorer forest regeneration, which reduces its value as a working forest and increases the threat of development. It also releases methane which would not be released if used for heating. Under management plans, the vast majority of our second- and third-growth generation forests will be healthier, more valuable, and therefore more sustainable. To paraphrase Commissioner of Vermont Forests, Parks, and Recreation Mike Snyder: In order to afford healthy forests, we need a healthy forest economy.

Consumers have a role to play. Choosing to heat with wood in a clean-tech, EPA-approved appliance (see Sin 7) offsets the use of fossil fuels.


5. We should focus on biochar & other promising technologies.


Wood is a bridge fuel that offsets geologic carbon while we transition to biochar, cold fusion, algae, biogas, or any number of other technologies on which good people are thankfully working. This is incredibly important as we move from technologies that are sustainable in the near term to others, like biochar that are regenerative,

The thing that sets wood chip and wood pellet heating apart is that we currently have a fully-functional infrastructure. It has taken over a decade for that industry to mature here in the US. Not to mention that in parts of Europe they have been heating with wood pellet boilers for over 30 years. The US wood pellet central heating industry was able to ramp up in only a decade because they went to school on that experience!

Private companies have invested millions in automated wood fuel delivery trucks and wood heating technology. State governments have committed millions of dollars in incentives for switching to wood heat in Maine, New Hampshire, Vermont, Massachusetts, and New York. Not to mention the army of installers and service contractors that are the foundation of market adoption.

In some cases, new heating technologies are already possible, but that is still a long way from from a fully-functional, real-world, mature industry, supported by heating contractor buy-in.

Even with all that in place, consumer adoption is another slow, heavy lift. Given the urgency of the climate crisis, we need to offset fossil fuels with wood now while we concurrently develop and perfect the industry infrastructure to support newer options. Consumers don’t take chances with their winter comfort.

6. Let's not let trees be the new coal.

Using coal or wood for electric generation is a bad idea.

Virtually no one heats with coal any more but across the globe electric generation from coal is the worst offender of greenhouse gas emissions. Burning wood for electric generation is just as bad.

We have cleaner ways of generating electricity than wood but for homes and business that heat with a central heating furnace or boiler our only choices are oil, gas, or wood.

It is essential that we ramp up clean electric generation with the urgency of a new Manhattan Project. Not only do we need to scale renewable generation, we need smart grids, distributed systems, and better storage. While we work on that, consumers can monitor the fuel and carbon mix of their local utility by searching out the utility’s Disclosure Statement.

We are not doing ourselves any good to switch to electric heating (or an electric car for that matter!) if the utility is generating electricity by burning coal.

Let’s not besmirch the reputation of wood pellet heating because there are better options for electric generation. Switching from oil or gas heat to a green-tech pellet boiler or furnace is the best thing any of us can do to reduce our carbon footprint.

7. Heating with wood is bad for human health.

Annual Particulate Emissions for Residential Heating Systems

The EPA has required  pellet boilers to have lower emission than oil or gas since 2015. The 2020 standard is even stricter.

The picture that we have in our minds of a dirty, sooty, pre-1988 wood stove is obsolete. Modern wood and pellet stoves have gone from an annual PPM of 280 all the way down to 4.5. The EPA continues to update the standard, and in 2020 the new requirement for wood and pellet stoves will be 2 PPM annually.

That’s still nothing compared to a modern pellet boiler which at 0.32 ppm has half the emissions of oil and gas boilers. In 2020 that standard will again be lowered to 0.10. The EPA is not updating the standard for oil and propane boilers which are currently at 0.80 and 0.51 respectively.

There is no free lunch when it comes heating our homes and businesses.

Just like emissions from cars, trucks, airplanes, and cruise ships heating emissions are not good for human health. But even there, pellets are the better choice. Emissions from wood heating is a know irritant, but emission from fossil fuels are a known carcinogen. You choose.


Heating is a complex subject. It’s technical, it’s hidden in the basement so we don’t think about it much, and most of us are simply stuck with the heating system we’ve got. Forest dynamics are also complex. Different regions have different pressures, and the decision to focus on preservation or conservation can get pretty granular. From green jobs to the new carbon economy this is a conversation worth having. As long as you’ve taken the time to read through the Seven Deadly Sins if you would like to leave a respectful comment we’d be happy to add your thoughts to the discussion.