The article “What is the best firewood to burn in a sauna” presents the most commonly used firewood in Finland.
Which wood gives the most heat?
Which wood produces the most soot?
All these questions are answered in this article.
You should only choose dry logs for your sauna heater. But which is the best firewood? I don’t think there is just one answer to this question.
You should never use wet wood, so-called waste wood, i.e. painted or varnished wood or other waste, in a sauna heater.
Fresh wood normally has a moisture content of 40-60%. The moisture content is influenced by the location, the type of wood and the age of the wood. The moisture content also varies in different parts of the wood. The moisture content of hardwood also depends on the seasons.
Logs should have a moisture content of 15-20%. This is usually achieved by drying for 4-6 months.
You can also speak of overaged firewood that has been dried for two summers.
What is the best firewood to burn in a sauna?
Birch
In Finland, the prevailing opinion is that birch is the best firewood. However, this is not necessarily the case. Birch is the best and densest wood in terms of calorific value. Birch wood also smells wonderful when it burns. However, birch soots more in the stove and chimney. This can lead to a soot fire in the long term.
This is why you should burn other types of wood with birch. Mixed wood keeps the stove and chimney “clean”.
At the moment, firewood dealers have increased the price of birch logs. It is therefore not a bad idea to burn other wood from time to time.
Pine
Pine is a slightly softer wood than birch and burns faster than birch.
But it is very suitable as firewood. However, it should be noted that pine leaves more ash and the stove needs to be cleaned more often.
Pine resin can also cause a certain amount of crackling, but not as much as when burning spruce. Pine burns well, is readily available and cheaper than birch.
Spruce
Spruce has a slightly lower density than pine. Spruce resin can cause crackling and flying sparks in the firebox. The ash can also contaminate the stove. Spruce wood is easy to ignite.
However, according to the KIUAS study, spruce is the most environmentally friendly.
One advantage of conifers is that they dry out more quickly than birch or aspen, for example.
Alder
Alder burns in the oven with a large flame and gives a good, “soft” fire. Alder wood chips are also used for smoking and give fish, for example, a great aroma.
Aspen
Aspen is not a well-known firewood, but can be used as a good kindling. It ignites well compared to other firewoods. Aspen can also have a slight crackling effect. Aspen needs just as much time to dry as birch.
Which wood provides the most heat?
According to studies, in this order
Birch
Pine
Spruce
Alder
Aspen
Which wood produces the most soot?
According to a study by the KIUAS project at the University of Eastern Finland, pine has the highest soot content and spruce the lowest.
The highest concentration of particulate matter was found in alder and birch with bark. The lowest in spruce.
The carbon monoxide concentration was highest in alder with bark and lowest in pine.
The highest nitrogen oxide concentration was found in alder.
In terms of emissions, nitrogen oxide concentrations were 13-30 % lower in unbarked trees. Soot concentrations, however, were higher in unpeeled trees.
They were 30 and 40 % higher for birch and alder respectively. In the case of PM1 concentrations, only alder was affected, with the values for unpeeled trees being up to half as low as for peeled trees. PM1=particles with an aerodynamic particle size of less than 1µm.
Why should wet wood not be burned?
When burning wet wood, the water must first evaporate and only then can the wood generate heat energy. In other words, the more water the wood contains, the less heat is generated.
Burning wet wood also significantly increases the amount of harmful emissions.
You can find out more about the effects of different types of wood on emissions in the KIUAS project at the University of Eastern Finland.
Why shouldn’t waste be burned in the sauna heater?
Brown corrugated cardboard and milk cartons increase the number of dirt particles many times over compared to burning clean wood.
Carbon dioxide and nitrous oxide emissions and their fluctuations were also higher.
Cardboard and milk cartons produce large amounts of ash in the stove, which affects emissions over longer periods of time.
What size firewood is good?
The length of the firewood should match the length of the grate, in most stoves 25-35 cm long. The diameter of a log is about 10 cm, i.e. at most the thickness of a man’s wrist.
At the beginning you should burn smaller logs, later you can add slightly thicker logs.
Of course, there are also other woods that can be burned, such as oak, beech and ash, which are more expensive as precious woods and take longer to dry. If you have fallen trees in your garden, you can of course also burn them as long as they are stored and dry.
To summarize, it is advisable to burn mixed wood in the sauna heater. Each type of wood has its own characteristics and advantages.
In addition, it is important to keep the stove in good condition and to check that everything is in order in the firebox and chimney.
Have a good time in the sauna!
With love,
Sauna-Kati
