Firewood: Quality Fuel Is Crucial To Successful Wood-Burning Appliance Operation & An Enjoyable Fire
You may not think that the type of firewood you choose to burn or the way you stack or store it much matters, but it does! In order to understand why, it’s important that you have a basic understanding of the combustion process.
What’s Needed For Combustion To Occur?
While the process of combustion is complex and technical, I can break it down simply like this: Fuel, air, and heat must be present for combustion to occur, regardless of what fuel is used or what appliance is used.
In a solid fuel-burning heater (like a wood stove), heat breaks up wood molecules, causing carbon and hydrogen to mix with oxygen from the incoming air, turning it into more heat, chemicals, and gases.
If any of the three required elements (fuel, air, heat) is removed from the equation, combustion stops. If all three occur in the proper ratio, combustion is self-sustaining.
- If complete combustion occurs, only water vapor (H2O), carbon dioxide, heat, and ash are produced.
- If incomplete combustion occurs, carbon monoxide, volatile hydrocarbons (creosote), as well as H2O and ash are produced.
The Stages Of Combustion
For the purpose of burning wood, there are four main stages of combustion:
- Stage I: Drying — As the fuel is heated, any moisture it contains is evaporated. Evaporation absorbs heat. Green wood has a higher water content, which means more heat is needed for evaporation to occur. This is heat that is lost.
- Stage II: Pyrolysis — When the wood is dry enough, the temperature will rise to the point where molecules making up the chemical structure of the wood will break down and vaporize, turning to hydrocarbon gases. This mixture of tar fog and combustible gases is not yet hot enough to burn and heat is still being absorbed at this point.
- Stage III: Gas Burning — As the temperature increases, the tar fog and hydrocarbon gases reach ignition temperature in the presence of oxygen, oxidizing and burning.
- Stage IV: Charcoaling — At the point during combustion when everything except carbon has burned off, charcoal remains. This carbon must come into direct contact with oxygen in order to burn — burning with little or no flame. Water vapor continues to be produced because of the mixture of hydrogen and oxygen from the combustion air.
Start With Good Wood
Since the first two stages of combustion actually absorb heat, I can see how crucial good, dry wood (wood with a moisture content of no more than 20%) is to heat production. But good, dry wood will also reduce creosote buildup and chance of chimney fire. Water vapor condensing in the flue and unburned volatile hydrocarbons sticking to that water vapor is what creates glazed creosote, the main cause of all chimney fires. So start with good wood and enjoy more heat, a better fire, and a cleaner, safer chimney system!
This barkless log looks dry
The end of the log appears dry
The moisture meter with the probes only halfway inserted reveal over 20% moisture
When I probe the middle of the log I get 30% moisture.
- Good logs, not rotting and punky, should be cut, split, stacked, and allowed to season (dry) for at least a year.
- Wood should be stacked where it will get long days of sun and good airflow going through the stack.
- Wood stacks should be covered on top or kept out of the weather.
Keep in mind that stacks should never be wrapped with tarps or plastic, as this will not allow moisture to escape, and will shield the stack from good airflow.
Have more questions about what type of firewood to buy or how to properly season and store wood? Feel free to give me a call at 208-550-8474. I am here to be a helpful local resource!