Hemlock is a common softwood often considered for firewood. While safe to burn, it is not generally regarded as a premium heating fuel. Its use is adequate, especially when mixed with denser wood types. Understanding its specific burn characteristics is necessary for using it effectively in a fireplace or wood stove.
Hemlock’s Heat Output and Density
Firewood heat output is measured in British Thermal Units (BTUs) per cord. Hemlock generally produces 15.9 to 19.3 million BTUs per cord, placing it in the middle range for softwoods. This output is significantly lower than dense hardwoods like oak or hickory, which can exceed 24 million BTUs per cord.
This difference in heat output is directly related to the wood’s density (mass per volume). Hemlock is less dense, meaning a cord contains less actual wood fiber than a cord of hardwood. Because all wood species produce roughly the same energy per pound of dry material, the lower density of hemlock results in a lower total BTU rating per cord.
Hemlock burns hot and fast, which can quickly warm a space. However, this rapid burn time requires frequent stoking and replenishment compared to slower-burning hardwoods. It is often best used as a “shoulder season” wood when less sustained heat is needed, or for quickly building a hot coal bed before adding hardwood.
Managing Creosote Buildup and Smoke
A common misconception is that softwoods inherently create more creosote than hardwoods, but the primary factor is the wood’s moisture content and the resulting fire temperature. Creosote is a highly flammable, tar-like residue that forms when smoke cools before exiting the chimney, and wet or unseasoned wood creates cooler, smokier fires.
Properly seasoned hemlock (moisture content below 20%) produces a low amount of creosote. However, softwoods are sometimes easier to burn when wet compared to hardwoods, and burning unseasoned hemlock produces excessive smoke and accelerates creosote deposits. Creosote accumulation presents a serious fire hazard, as it can ignite and cause a chimney fire.
Hemlock is known to pop and spark more than many hardwoods, posing a safety concern in an open fireplace. This sparking is due to the wood’s structure and the rapid release of trapped pockets of air and moisture. For this reason, a fireplace screen or a closed wood stove is recommended.
Practicalities of Seasoning and Splitting
Hemlock is known for its relatively fast seasoning time, which is a significant advantage. While hardwoods often require 12 to 18 months or more to dry, hemlock can typically be seasoned in a shorter period, ranging from 7 to 12 months, depending on the climate. Splitting the logs and ensuring adequate airflow in the stack are important steps to reach the target moisture level quickly.
The wood is generally considered easy to split, especially when green. Its straight grain structure minimizes the effort required for processing the logs. This ease of preparation makes hemlock a convenient option for users who handle their own wood.
A frequent public concern regarding hemlock is its potential toxicity, stemming from confusion with the unrelated poisonous herb, poison hemlock. Hemlock tree wood is not toxic and is safe to burn in a residential setting. It is an acceptable, readily available softwood when its specific burning characteristics are accounted for.