Automated Wood Heat
Q: Why did the Northern Forest Center commission this study?
A: People have questions about the climate impact of wood energy and we felt there was a need for unbiased science-based information on the specific impact of using the region’s wood pellets for heat. Previous studies and media have reported a wide range of results regarding greenhouse gas without clearly distinguishing between the impacts of using wood for heat versus electricity or assessing the full life-cycle impact of the fuel.
Q: Who did this study and what makes them credible?
A: The study was conducted by John Gunn, Ph.D. and Thomas Buchholz, Ph.D. of the Spatial Informatics Group – Natural Assets Laboratory, a non-profit scientific research organization “with a mission to develop and apply the scientific foundation needed to link economic and environmental interests by accounting for the full value of natural assets.” They have broad experience in forest ecology, forestry, carbon accounting, and related topics.
Q: What does this study assess?
A: Our study looked specifically at a life-cycle analysis of the greenhouse gas impacts of using wood pellets from local mills for heat in the Northern Forest. “Local mills” include 9 of the 10 mills serving the region (one mill did not respond to our survey).
Q: What makes this study unique?A: This study is based on real data from local mills and actual forest harvesting data; it is specific to using these pellets for heat. No other study is this specific. The research scientists found that from day one, using wood pellets for heat reduces greenhouse gas emissions by 54% compared to oil and 59% compared to natural gas.
Q: Since trees grow back, isn’t wood heat carbon neutral?A: We describe wood heat as “carbon better.” On a macro scale, wood heat can come very close to carbon neutral over the long term, if the overall stocks of forest in the region remain constant or increase. Making and transporting the pellets generates greenhouse gas emissions; this impact, which was calculated from real data provided by the mills, is incorporated into the life-cycle analysis. (Extraction and transportation of fossil fuels was considered in the analysis as well.) Bottom line, wood pellets produce far less greenhouse gas than oil and natural gas when used as a heating fuel in the Northern Forest region, when you consider the entire life cycle of the fuels.
Q: What’s the difference between “greenhouse gas” and “carbon” emissions?A: Strictly speaking, “carbon” is an element and “greenhouse gases” are a group of gases that trap heat in the atmosphere. Carbon dioxide makes up the vast majority of greenhouse gas in the atmosphere. Greenhouse gas impact is typically measured in carbon dioxide equivalents (CO2e). The terms greenhouse gas emissions and carbon emissions are often used interchangeably.
Q: I heard conflicting information about the carbon or greenhouse gas impacts of using wood. What should I believe?A: Results depend on many factors, including whether the wood is generating heat or electricity, whether the results report emissions from combustion only or assess the full life-cycle impacts of the fuel, and specifics related to how the fuel is sourced, processed and delivered. In short, context matters.
Our study assesses the greenhouse gas impact of using wood pellets produced by local pellet mills for heat in the Northern Forest. In that context:
- From day one, using wood pellets for heat reduces greenhouse gas emissions by 54% compared to oil and 59% compared to natural gas.
- In 50 years, GHG emissions from pellets drop to 62% less than oil, 67% less than natural gas, and 56% less than propane.
Some reporting of past studies failed to specify the type of energy being produced and has resulted in incorrect generalizations. For instance, the actual results of a study conducted by the Manomet Center for Conservation Sciences (Biomass Sustainability and Carbon Policy Study) found that when it comes to heat, replacing heating oil with efficient wood pellet heat cut greenhouse gas emissions by 25% by 2050. Press coverage of the Manomet study, however, resulted in a range of misleading headlines.
Q: What about air source heat pumps as a low-carbon heat source?A: Heat pumps can be a low-carbon heating choice but that’s not always the case. If they’re connected to the electric grid, their greenhouse gas impact depends on the electric fuel mix (i.e. the source of the grid electricity – natural gas, nuclear, etc.). Solar-powered heat pumps are preferable from a carbon standpoint. Even then, heat pumps are rarely a whole-house heating solution and are usually backed up by fossil fuel heating systems. Also, heat pumps aren’t suitable for all houses – they work best in very energy efficient, open-concept homes, not so well in the older, less open and less well insulated houses common in this region.
Q: Does the source of wood used in the pellets make a difference?A: Yes. In general, the more sawdust (i.e. residue from a sawmill) that goes into a pellet, the lower the greenhouse gas impact.
Q: What about the potential for overharvesting the region’s forests?The Northern Forest has ample wood supply. In 2015 (most recent data available) the standing live inventory is 937 million cords of wood. Annual net growth is 21.6 million cords. Annual harvest is 12.6 million cords. Markets for low-grade wood (the type that is used in pellets) have been declining. Maine lost 36% of its low-grade market since 2013 through mill closures. This market change means that more low-grade wood is available for producing wood pellets without increasing the harvest rate.
Q: The study is based on Forest Inventory data for Maine – what makes it relevant for the rest of the region?A: The forest composition across the Northern Forest is consistent that the researchers felt comfortable using the Maine data from the Forest Inventory and Analysis National Program as a proxy for the entire region.
Q: Where did the pellet mill data come from?A: Nine of the ten mills in the Northern Forest completed a survey that asked, among other topics, about:
- Feedstock amount (green tons)
- % hardwood versus softwood species
- Source of feedstock (forest operations, primary wood processing facility, etc.)
- Type of feedstock from the forest (harvest residue, small diameter trees, etc.)
- Average transportation distance from feedstock source to the facility
- Total pellet production capacity and actual pellet production (most recent year and five year average)
- Electricity source (% grid, waste wood, solar, wind, other)
- Process heat source (% natural gas, wood waste, oil, etc.)
- Typical transport distance to the end user
Q: Wouldn’t the greenhouse gas impact be lower if we didn’t cut trees at all?A: If all trees could be left growing indefinitely, the greenhouse gas impacts would be lower. However, the forest does not exist in a vacuum. About 85% of the Northern Forest is privately owned, and landowners will decide how to use the trees on their land. Without markets for trees, many landowners would look for other economic opportunities, which could include clearing the land and eliminating the carbon sink permanently. In addition, forests are dynamic systems and are subject to destruction from invasive species, weather and fire.
The Center is not advocating that we increase harvesting to supply energy markets. Rather, we believe that using some of the harvested wood (much of it residuals from other purposes) for wood pellet heat to replace fossil fuels will cut greenhouse gas impacts by more than 50%, starting immediately.
Q: Isn’t natural gas better than oil from a climate perspective?
A: When you account for the full life cycle – including methane leakage associated with natural gas distribution – natural gas has higher greenhouse gas emissions than heating oil. Methane is a greenhouse gas 30 times more carbon intensive than carbon dioxide, so even a small amount of methane emissions has a major effect. This “distribution loss” (Alvarez et al., 2012) is often excluded from discussions of the climate impact of natural gas.
2006 IPCC Guidelines for National Greenhouse Gas Inventories
ForGATE - A Forest Sector Greenhouse Gas Assessment Tool for Maine: Calibration and Overview
Proceedings of the National Academy of Sciences of the United States of America - “Greater focus needed on methane leakage from natural gas infrastructure”
Analysis shows wood pellet fuel reduces greenhouse gas emissions by more than half over fossil fuels
The Northern Forest Center commissioned an independent third-party study of the greenhouse gas impacts of heating buildings with state-of-the-art wood pellet boilers. The Spatial Informatics Group-Natural Assets Laboratory (SIG-NAL) used data specific to the region’s forest composition and harvest practices, and the pellet sourcing and manufacturing of 9 out of 10 Northern Forest pellet mills, all of which produce pellets exclusively for thermal (heat) generation.
The life-cycle analysis, which accounts for all greenhouse gas emissions from sourcing, processing, and transporting fuels, finds that:
On day one, using wood pellets for heat reduces greenhouse gas emissions by 54% compared to oil and 59% to natural gas.
After 50 years, greenhouse gas emissions from pellets drop to 62% less than oil, 67% less than natural gas, and 56% less than propane.
For more information, take a look at a fact sheet summary.
The analysis by Thomas Buchholz, PhD. and John Gunn, PhD., Spatial Informatics Group-Natural Assets Labratory (SIG-NAL), has been peer reviewed and published in the journal Energy.
Net Emissions Comparison
Almost half of pellet content recaptured from other uses
In 2015, the average Northern Forest- produced wood pellet was comprised of:
- 44% sawdust and other byproducts of forest product manufacturing—wood that was cut for other purposes;
- 56% low-quality pulpwood and small trees, usually the byproduct of harvesting for higher value timber;
- Less than 1% from other sources, such as landscaping and municipalities.
About the Study
SIG-NAL analyzed the greenhouse gas impacts of using modern wood heat in the Northern Forest using a forest sector life-cycle assessment tool and data not previously available.
- The mix of energy sources used in pellet production at 9 of 10 mills in the region;
- Harvest levels. The results described in this summary are based on forest harvesting at 2015 levels, with the assumption that increased demand for pellet fiber is offset by reductions in other markets (see page 2) for no net increase in harvesting;
- Tree regrowth; and
- Forest dynamics and natural impacts that can affect unharvested trees and result in release of stored carbon.
Measuring the greenhouse gas impact of any heating fuel requires accounting for all emissions in production and use of the fuel, including:
- All the greenhouse gases associated with producing the fuel (including extraction or harvesting, manufacturing or processing, transportation);
- Greenhouse gases emitted by the fuel when used;
- Efficiency of the heat generation system being used; and
- Carbon stocks in the forest such as live and dead trees (in the case of using wood).
SIG-NAL used US Forest Service forest inventory data to define forest types and age classes for 2 representative wood supply areas within a 50 mile radius of the pellet plant, and used growth and yield projections from the Northeast Variant of the US Forest Service Forest Vegetation Simulator (FVS-NE) to examine the results of forest management options. SIG-NAL derived initial stand type and tree lists from Maine FIA plot data, which due to similarities across the Northern Forest, provided a reasonable estimation of growth response to management at the landscape scale. SIG-NAL used a new pellet life cycle assessment module for the ForGATE Forest Sector Greenhouse Gas Assessments Tool for Maine1 to calculate total emissions for scenarios with and without pellet mills. (1Hennigar, C., L. Amos-Binks, R. Cameron, J.S. Gunn, D.A. MacLean, and M. Twery. 2013. ForGATE - A Forest-sector GHG Assessment Tool for Maine: Calibration and Overview. Gen. Tech. Rep. NRS-116.
Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 54
Why markets for wood pellets help save forests from development
Changing markets make room for pellet production
Forests—and changing markets—provide the opportunity to reduce greenhouse gas impacts by heating with local, renewable wood pellets instead of fossil fuels.
Major traditional markets for low-grade wood, such as paper making, continue to shrink in the Northern Forest. The drop in demand creates an opportunity to shift pulpwood toward pellet manufacturing.
- Eleven pulp mills have closed in the Northern Forest since 1999, reducing demand for low-grade pulpwood.
- Between Oct. 2013 and April 2016, Maine lost 4 million tons, or 36%, of its low-grade wood market. Most of this reduction is not reflected on harvest volume graph at right.
Landowners rely on markets for low-grade wood that is harvested to improve long-term timber production, recreation and more. Pellets are an important part of the low-grade wood market. Steady markets for low-grade wood help landowners maintain forestland instead of converting it to non-forest uses such as development. See how we're working to drive demand for efficient pellet heat.
Forest volume context
An analysis of 2015 forest inventory data shows that the live volume of timber in forests in Maine, New Hampshire, New York, and Vermont is increasing. Annual forest net growth exceeds annual harvest.
- Net Growth: 21.6 million cords annually.
- Harvest: 12.6 million cords annually.
Subsidies will help you switch to local, renewable heat!Join the Northern Forest Center at the Burke Town School from 6-8pm on October 4 to learn more about modern wood heat and subsidies available for wood pellet boilers/furnaces. You’ll be able to tour the school’s pellet boiler, chat with vendors, and check out a demonstration boiler. All attendees will be entered into a drawing for a ton of premium wood pellets from Renewable Fuels of Vermont! Light refreshments will be served.
Homeowners in the Northeast Kingdom can receive $8,000 in subsidies towards installing a wood pellet boiler or furnace. Generous subsidies will soon be available for commercial and public buildings as well. These systems are efficient, clean, convenient, and cost-effective, and use a renewable, local fuel that supports the local forest economy.
When: Tuesday, Oct. 4th 6-8pm
Where: Burke Town School 3293 Burke Hollow Road, West Burke
To learn more about local, renewable heat with wood pellets, visit our Modern Wood Heat page.
These incentives are a part of the Northeast Kingdom Model Neighborhood Wood Heat Initiative. Learn more about the subsidies here.
Here are some answers to Frequently Asked Questions.
Modern wood pellet boilers are an economical, highly-efficient, and convenient choice for heating your small commercial space or home. “Heating local” with Northern Forest pellet retains wealth instead of sending it elsewhere—heating with oil sends 87% of wealth out of the region. Over time, heating with a pellet boiler will reduce your impact on climate change and helps keep forests as forests.
Pellet boilers are virtually seamless replacements for traditional oil-based systems. Minimal changes to the home heating system are required (depending on distribution system), and your oil boiler can remain in place if flue space allows. This graphic from the German Renewable Energy Agency shows a typical installation:
What are the main advantages of modern wood heat?
- Local Economic Benefits: “Heating local” with Northern Forest pellets retains wealth instead of sending it elsewhere (78% of money spent on oil leaves the region) and creates or sustains jobs.
- Fuel Cost: Premium wood pellets currently cost about 40% less than heating oil.
- Fuel Resource: The forest resource is renewable and locally available, and provides a more stable source compared to imported fuels traveling through global transportation networks.
- Consumer Convenience: Modern wood pellet boilers are automatically fed by contained storage bins and refilled by bulk delivery trucks on a regular basis – no pellet handling is involved, and maintenance is minimal.
- Particulate Emissions: Replacing an outdoor wood boiler or wood stove with a modern pellet boiler dramatically reduces a household’s particulate emissions.
- Local Pride: Just as consumers have endorsed local food in recent years, they are beginning to understand the value of local heat as well. Many northern communities have a rich forestry legacy and residents feel proud to support it.
- Carbon Footprint: As discussed below, using wood heat instead of fossil fuels leads to a net reduction in carbon dioxide emissions over time.
What are the downsides of heating with pellets, and what’s being done to address them?
- Burning wood releases air pollutants, but high-efficiency modern systems emit just marginally more particulates than oil or gas heating systems. See below section on air quality.
- Forest resources are limited. Conservative estimates suggest that only 18.5% of the Northeast could be sustainably heated with wood, but we are nowhere close to that level and the region’s forests are currently growing more than they are being harvested.
- The carbon impact of wood heat is variable. Accurate carbon accounting must consider factors such as time, land use change, forest management practices, and the type of fuel being displaced by biomass. Biomass can be a low carbon fuel when harvested sustainably from land that is managed well over time, but it’s not guaranteed.