Last updated May 16, 2023
Most of the new wave saunas in the UK are wood-fired. The classic Finnish sauna is wood-fired as well. Fire is one of humanity’s first discoveries. In Greek mythology Prometheus stole it from the gods and gave it to humanity, leading to the birth of the civilisation. In more immediate terms, wood fire is often the go-to source of heat and the flickering flames, fragrant smoky notes in the air and ambient sounds of the fire add to the atmosphere of the sauna experience. This note aims to capture the key concepts and complexities related to modern day wood burning and best practices in sauna context. #WIP
Fire or, technically, combustion is a chemical reaction where fuel (e.g. firewood) is gasified and starts to react to oxygen – generating heat and light. A fire needs: fuel, oxygen and heat. In the case of wood-fire, it’s the carbohydrates in the wood that gasify and combine with oxygen in the air, releasing heat.
By-products of wood burning are
Apart from perhaps water vapour, all other by-products come with various levels of concern, which is why wood burning knowledge matters.
The absolute cleanest combustion-based sauna stove would be hydrogen-fired, generating only heat and water vapour (2H2 + O2 → 2H2O). One day we’ll get there.
Purpose-grown firewood is practically renewable and carbon-neutral. From a big picture CO2 perspective there’s not much to worry about. CO2 (and water vapour) is actually a result of a good burn. Bad burn produces poisonous CO and particulate matter.
Dry firewood is a must. According to the VTT (the Finnish National Technical Research Centre) emissions are five-fold when firewood moisture content is 40% instead of recommended 15%.
Wood can be either air or kiln dried.
However: