Eucalyptus is a fast-growing hardwood popular in regions where it is readily available, such as California and other temperate climates. Its high density and rapid growth rate make it an attractive and sustainable fuel source. However, its unique composition, particularly the high content of volatile oils, means successful burning requires specific knowledge and preparation.
Evaluating Eucalyptus Heat Output
Eucalyptus, particularly the common Blue Gum varieties, is classified among the highest-density hardwoods. This density translates into a high British Thermal Unit (BTU) rating, measuring the heat energy produced per cord of wood. Fully seasoned eucalyptus typically yields around 34.5 million BTUs per cord, often exceeding that of traditional hardwoods like red oak (24 million BTUs per cord) or Bigleaf Maple (22.7 million BTUs per cord).
The tight grain structure means more combustible material is packed into each piece compared to less dense species. This allows eucalyptus to burn very hot, providing intense heat quickly and for a sustained period. Fully dried eucalyptus is an excellent choice for a primary heat source during cold weather. However, the heat output is heavily dependent on the wood achieving a low moisture content, a requirement more demanding for this species than for others.
Understanding Volatile Burning Characteristics
The defining characteristic of eucalyptus combustion is the presence of flammable aromatic oils within the wood fibers. These oils cause the wood to ignite aggressively and burn with high intensity, resulting in a rapid flame and heat release. While the intense heat is desirable, the volatile nature of the oils also causes the wood to pop and spark excessively during combustion. Burning eucalyptus in an open fireplace without a protective screen poses a safety hazard due to these flying embers.
This rapid, aggressive burn rate can also make eucalyptus challenging to manage in certain wood stoves or furnaces. Some users report a long, hot burn, while others find it consumes quickly, necessitating more frequent loading compared to slow-burning wood like seasoned oak. The high oil content means that even properly seasoned wood can have pockets of volatile compounds, contributing to erratic and intense burning behavior.
Essential Preparation and Seasoning
Burning eucalyptus relies on extensive and proper seasoning due to its high initial moisture content and density. Freshly cut wood contains significant water that must be reduced to below 20% for efficient burning. Achieving this low moisture level typically requires a minimum seasoning period of 18 months, and often two full years are necessary for optimal results. Attempting to burn green eucalyptus results in excessive smoke and wasted energy used to boil off the moisture.
The wood should be split soon after it is cut, ideally within a week, because the grain tends to twist as it dries, making splitting difficult once seasoned. Splitting the wood into smaller pieces increases the surface area exposed to the air, accelerating the evaporation of water. Stacking the split wood to allow ample airflow and keeping it protected from rain are necessary steps to achieve the low moisture content required for a clean, hot burn.
Maintenance and Safety Considerations
The high oil content that gives eucalyptus intense heat also presents an issue for the long-term safety and maintenance of the chimney system. When wood burns, volatile gases are released; if the chimney flue temperature is too low, these gases condense on the walls, forming creosote. Burning poorly seasoned eucalyptus, or burning it in a slow, smoldering fire, produces more smoke and results in a rapid buildup of this tar-like substance.
Creosote is highly flammable and is the primary cause of chimney fires, which can be intense and cause significant damage. Even when properly seasoned, the high heat and oil residue from eucalyptus necessitate diligent chimney care. Homeowners using eucalyptus as a primary fuel source should schedule professional chimney inspections and cleanings more frequently than the standard annual recommendation to mitigate the risk of a flue fire.