Wood Energy and the Environment

Forest Products Laboratory retiree John Zerbe has told us about the many ways that wood is used as a form of energy, but how does its use affect the environment? The Forest Service has chosen climate change as one of its top areas of concern; therefore, this question is of great interest. Zerbe breaks the matter down for the reader.

This old stove is quaint, but not the best for the environment. Photo by Victor Grigas via Wikimedia Commons

This old stove is quaint, but not the best for the environment. Photo by Victor Grigas via Wikimedia Commons

Carbon Dioxide

The increasing accumulation of carbon dioxide and other greenhouse gases in the atmosphere is generally considered to be a threat to future stability of the earth’s climate.

There can be no doubt that our vast use of fossil fuels is the major contributor to increased atmospheric carbon. The renewability of wood and other biomass fuels makes them a desirable alternative to fossil fuels to prevent or retard increasing retention of carbon dioxide emissions. When new trees are grown to replace the wood that was the source of the fuel, carbon is constantly used and regenerated in the growth cycle. The carbon that is emitted to the atmosphere is absorbed by photosynthesis in new growth.


Sulfur emissions to the atmosphere are undesirable because they can precipitate and cause harmful acidic conditions in soil and water. Wood contains little sulfur, but some coal and some oil contain substantially more. Therefore, sulfur emissions from wood are more easily controlled than those from their fossil fuel counterparts.

Oxides of Nitrogen

Oxides of nitrogen emissions tend to be lower with wood fuel than with fossil fuels. On the other hand, forest fires are a major source of nitrous oxide (a greenhouse gas) in the atmosphere. Higher oxides of nitrogen emissions usually accompany combustion at higher temperatures. New technology stoves designed to be more efficient have higher oxides of nitrogen emissions than conventional stoves.


Emission of particulates is the most common cause for concern in meeting environmental requirements with the burning of wood fuel. In the United States in some municipalities and under some atmospheric conditions, particularly air inversions, there are periods when wood burning in fireplaces and stoves is not permitted. Catalytic stoves can help in attaining lower emission rates. Inefficient stoves, such as outdoor wood boilers, which more and more places are banning, have been correlated to increases in asthma and other breathing difficulties.

Altogether, with increasingly sophisticated technology in wood stoves, fireplaces, and furnaces, wood is a more benign source of energy than fossil fuels as well as being renewable. FPL’s Mark Knaebe states that, “Burning wood efficiently can actually be better than letting it rot in the woods because a significant amount of methane is produced during decay.”

Wood Pellets: Today's Choice for Wood Energy

In his overview of wood as fuel and a source of energy from the Encyclopedia of Forest Sciences, Forest Products Laboratory retiree John Zerbe reviews chips and sawdust, shavings, manufactured fireplace logs, and briquettes as sources of wood energy, but here at FPL, we know that wood pellets are the most popular alternative to cordwood for heating.


Zerbe and FPL Natural Resources Specialist Mark Knaebe state that wood pellets are becoming increasingly popular. Pellets are made from processed, ground, debarked logs held together with a binder. When pellets are made from clean wood with little bark, the ash content is low.

Pellets are sold at retail outlets in 40-pound sacks, which handle and store easily. The consumer can purchase pellets in bulk, including in one-ton bags, which can be replenished by a truck delivery. Knaebe says, “Bulk pellets are just like with oil heat: the truck will come and fill your container, and your thermostat tells an auger to feed your boiler or furnace. The pellets should be kept dry to prevent disintegration and to avoid risk of mold and decay.”

“In very large piles of pellets,” warns Knaebe, “you will get a fire about 3 weeks after the pile gets wet because of spontaneous combustion and the high insulating properties of a big pile. This can be prevented with blowers or making smaller piles, never more than 10 feet deep.”

Sometimes pellets for cooking are made from woods with special flavors that can be used in barbecuing, directly or with charcoal or gas, for conveying this flavoring to meat or poultry. Excellent pellet grills are available now. However, the most common use of pellet fuel is for heating with modern and convenient pellet stoves. Some of these stoves have automatic ignition, feed, and control systems. To be EPA certified, they must be 78% efficient. To determine the efficiency of your fuel, you can download FPL’s popular Fuel Value and Power Calculator.

How Wood Is Used for Energy


Metapolisz Images through Wikimedia Commons

Doesn’t that fire look inviting? So what’s the scoop on firewood?

According to John Zerbe and FPL’s Mark Knaebe of the Forest Products Marketing Unit, cordwood is the most common kind of wood fuel we like to burn. The most common way of using cordwood for fuel is to burn pieces about 1–1 ½ feet long that are split from logs. We burn much of such wood in our fireplaces and wood stoves today, and, formerly, such firewood provided the main fuel source for home heating, domestic hot water, and food preparation. Wood is still used for heating some homes in industrial countries. Usually heat is not produced efficiently in fireplaces, but some fireplaces are sealed with glass doors and designed to use blowers to be more effective. Stoves and furnaces burn firewood more efficiently and are getting much cleaner.

However, for some applications, wood is converted to other forms of fuel that are more convenient, waste less energy, and are less prone to emit undesirable particulates and other pollutants to the air. Examples of other kinds of fuel are manufactured fireplace logs (firelogs), which are made from waste wood and wax to provide open-hearth warmth and ambience with clean fuel. More recently, however, the main alternative to cordword is wood pellets, the main advantage of which is their dryness and their ability to be automated.

Energy from Wood: An Introduction


Wood is renewable energy, as this circle indicates.

Brrrr! Here in Madison, Wis., home to the Forest Products Laboratory, we’re having some very cold temperatures. Doesn’t a wood fire sound comforting?

And as nice as a fire sounds in this neck of the woods, what about the use of wood for fuel in other parts of the world? Sifting through the words of wisdom from FPL retiree John Zerbe, let’s delve into his overview of wood as a fuel and source of energy from the Encyclopedia of Forest Sciences.

Zerbe informs us that wood and charcoal are the predominant fuels for heat and food preparation for the majority of citizens in most developing countries. In those countries, wood fuels are also important for powering small- and medium-size industries. Moreover, energy from wood continues to be important in industrial countries.

Wood energy is consumed in a variety of forms that include fireplace lengths, chunkwood, chips, sawdust and shavings, black liquor from pulp manufacture, pellets, fireplace logs, briquettes, charcoal, gasified wood fuel, and liquefied wood fuel. Wood provides warmth and comfort to homes via burning in fireplaces and automated heating systems. And even in industrial countries, wood is used for cooking where it is burned in specially designed stoves for convenience or on grills to bring out special flavors in food.

Wood fuel is important to commercial wood manufacturing facilities where waste wood can be disposed of and used profitably for energy at the same time. Some major considerations in using wood for fuel are environmental impact, economics, convenience, reliability, and simplicity. On balance, wood is an environmentally benign fuel. It tends to be more economic than some other fuels, but may be less convenient, as anybody who has cut and stacked their own firewood knows.

Here at FPL, we love to say “Wood is good.” In future posts, we will go on to discover the many ways wood is good for producing energy.