Arborvitae, a common landscaping shrub or tree from the genus Thuja, can technically be burned, but it is widely considered a poor choice for firewood. As a softwood, it lacks the density required for efficient heat production and carries specific characteristics that create safety concerns when used in a fireplace or wood stove. Homeowners often encounter this wood after storm damage or when removing overgrown hedges, leading to questions about its suitability as a fuel source. While not recommended for heating a home, the wood has limited utility, particularly for kindling or outdoor fires, provided the user understands and mitigates the inherent risks.
The Safety Risks of Burning Arborvitae
The primary safety concern with arborvitae wood is its high sap and resin content, which is typical of conifer species. This resin vaporizes during combustion and, when it comes to contact with cooler surfaces in a chimney or flue, it rapidly condenses into a highly flammable substance called creosote. Excessive creosote buildup is a leading cause of dangerous chimney fires. Therefore, burning arborvitae in an indoor wood stove or a closed heating system is strongly advised against, even when the wood is well-seasoned.
The wood’s volatile composition also contributes to an increased risk of sparking and popping, even after a long drying period. This occurs when pockets of trapped moisture or resin rapidly expand and burst, projecting small, burning embers from the firebox. For open fireplaces or outdoor fire pits, this sparking poses a fire hazard to nearby flammable materials, requiring the consistent use of a secure fire screen. Furthermore, the volume of smoke and particulate matter produced by resinous woods can be a respiratory irritant, making it unsuitable for cooking fires or poorly ventilated spaces.
Performance Characteristics as Firewood
Arborvitae’s performance as a fuel source is compromised by its extremely low density, which is among the lowest of domestic commercial woods (e.g., Thuja occidentalis is roughly 19 pounds per cubic foot). Since heat output is directly proportional to wood density, this low mass translates to a poor BTU (British Thermal Unit) rating compared to hardwoods. Consequently, a cord of arborvitae yields significantly less heat than a cord of dense oak or maple.
This low density causes the wood to burn very quickly, resulting in a short, intense flash of heat rather than a slow, sustained heat for warming a space. The rapid burn rate means that a user must refuel the fire frequently, making the wood highly inefficient for primary heating purposes. The smoke often has a pleasant, spicy, or cedar-like aroma, but this scent is a byproduct of the same resins that contribute to creosote formation. The wood’s characteristics make it better suited for use as kindling, where a quick, hot flame is desirable to ignite denser logs.
Essential Preparation for Burning
For those who choose to burn arborvitae, proper preparation is necessary to minimize inherent risks and maximize limited heat output. As with all firewood, the wood must be seasoned to reduce its moisture content to below 20 percent. Due to the high internal moisture and resin content, arborvitae should be allowed to dry for at least six to twelve months, despite being a softwood.
The seasoning process should involve splitting the wood into smaller pieces immediately after cutting, as wood dries primarily from the end grain. The split pieces should be stacked in a single row or with space between adjacent stacks to ensure maximum airflow and exposure to sunlight. Stacking the wood off the ground and covering the top protects it from rain and accelerates the drying process. Once fully seasoned, arborvitae is best reserved for outdoor settings, like fire pits or bonfires, where the risk of chimney fire and indoor smoke irritation is eliminated.