Wood Burning Stoves

As our population has become ever denser, pollution has become an increasing problem for all of us. During the winter months in many parts of the United States, fine particles and noxious gases from wood stoves were making up to 30% of the pollution problem. Because of this pollution almost all new wood stoves that are sold now must be certified before the dealers are allowed to sell them.

Wood fuel will go through three stages of combustion as the wood breaks down into heat. First stage; heat from the flame has to dry out any moisture that remains in the wood. If the wood is not adequately seasoned there will be a hissing sound and stream will rise off the wood. Because the heat produced at this stage is being used to burn off the moisture, there is very little residual heat left for other purposes.

As wood burns there are three stages that the wood fuel goes through as the fuel breaks down into heat. The first stage begins when the heat from the flame has to dry out any moisture that remains in the wood. If the wood is not thoroughly seasoned you will hear a hissing sound and see steam rise off of the wood. There is very little heat being given during this stage of combustion as all the energy of the frame goes to drying out the wood. Please review our article on preparing your wood for the heating season.

After the first stage has dried out the moisture, the second stage of combustion starts as the gases begin to rise off the wood. The heat is still inadequate to completely burn all the gases that are produced by the heat from the wood, instead the vapors escape up the chimney as unstable gases composed of VOCs (volatile organic compound), tars and charcoal or carbon which can affect the environment and human health. As the VOCs escape up the chimney the gases tend to cool and become very concentrated with moisture that is laden with creosote that clings to the walls of the chimney, and other pollution gases that are carried with the smoke particles.

Stage Three is the charcoal stage, where the wood actually produces heat. As the temperature goes above 600 degrees Fahrenheit, the gases start to burn; the gases are ignited by nearby flame. As the temperature reaches 1000 degrees and more the logs become charcoal that then emits the most heat.

A few examples to illustrate the different stages: If a homeowner uses freshly cut wood or unseasoned wood as the industry calls it, this wood has a moisture content of 40% to 60%. This means that as the wood starts to burn and break down into heat, the available energy (heat) that is produced just goes to dry out the moisture that is in the wood. This will extends stage one burn time so that when you finally get to stage two there is very little fuel left to heat the home.

For our second example: Let