Your sauna heater is only as good as the firewood you feed it. After all, you don’t want to run a Porsche on 89 Octane fuel. While your heater will combust almost anything, it is happier and higher performing when consideration is paid to species, moisture levels, size, and firebox stacking.

 

Species

 

If harvesting your own wood, you are limited to what you have around you, however for heating your sauna ideally you will want to use hardwoods over softwoods as they will burn with higher BTUs (British Thermal Units – the higher the BTU, the hotter the wood will burn). However, softwoods (like Cedar or Pine) work great as kindling. They dry faster and they typically have more sap which helps them quickly ignite. 

 

Hardwoods, being more dense, produce hotter and longer lasting fires. In Ontario the most readily available hardwood species are (BTUs in parentheses): 

 

• White Birch (20.2)

• Sugar Maple (24.0)

• Red Maple (18.6)

• Oak (26.2)

• Yellow Birch (21.8)

• Beech (27.5)

 

Any of these species, well-seasoned, will give you a great burn however it is also important to not keep your firebox too hot

 

Moisture Levels

 

Not only will seasoned (dry) firewood burn hotter, easier, and more efficiently, it is also safer and more environmentally friendly. Unseasoned (wet) firewood is harder to start, emits a lot of smoke, and uses the heat generated by the fire to evaporate the water in the wood leaving less heat for your sauna cabin. The excess smoke emitted by wet wood also increases the levels of creosote that accumulates inside your chimney which can add to your fire risk. Finally, the excess smoke generated not only costs you heat (smoke is energy), it is an unnecessary pollutant. 

 

Firewood from a freshly cut tree will contain 50% moisture. Ideal firewood moisture levels for sauna heating are between 15-20%. A good rule of thumb is to split your firewood in the spring for use the following year (some denser species like Oak can take up to 2 years to dry). I use a moisture meter (insert Amazon link) to test my wood before burning as I usually have several cords at various levels of dryness. If you don’t have a moisture meter you can usually tell if your wood is try by its cracked and greyish appearance. A telltale sign that your wood is still wet is if it sizzles in the firebox. 

 

Size and Stacking

 

For heating your sauna use smaller logs (2-4” diameter) cross stacked for airflow and speed. Once you have reached operating temperature use a mix of 4-6” logs to maintain heat. These logs can be more uniformly stacked to slow down the burn and wood use. Use at least three logs so form a sheltered pocket of glowing coals that sustains the fire and keeps it in the sweet spot.