If you fire up your wood stove, you can save gas or oil - especially important this winter. But firewood is not equal to firewood, if you can get any at all. Because dry firewood is currently in short supply. Here are the most important key figures and tips for wood provision.
Anyone who owns a wood-burning stove could have a clear advantage this winter. Because in view of the drastically rising prices for gas and oil, firewood is an alternative that makes it possible to switch on the central heating later in the year - and to switch it off earlier in the spring. This saves energy costs.
But this calculation will probably not add up for this year. "It's almost impossible to get dry firewood this year," said Gerd Müller, head of the office of the Federal Firewood Association in Kamen, at the beginning of July. Or to put it another way: If you know a forest owner or a forester or come across an offer in the trade: you are probably lucky. But if you have a wood stove, you usually have to buy it in advance anyway - because the wood has to dry first. Here are the most important key figures and advice for your pension provision:
cubic meter or solid meter?
Firewood is often sold in cubic meters (Rm), also called ster. Sometimes in southern Germany there is also talk of fathoms. A cubic meter is a cubic meter of loosely stacked wood including the cavities, explains the Industrial Association for House, Heating and Kitchen Technology (HKI) in Frankfurt. So there can be a lot of air between the wood. By the way: A fathom corresponds to around three cubic meters.
If a cubic meter of wood is stacked without cavities, it is a solid meter (Fm). This corresponds to a cube that is one meter wide, one meter high and one meter long. A bulk meter (Srm) is a cubic meter of loosely packed wood with cavities.
Oven owners should therefore also pay attention to the unit when buying. Because depending on whether it is soft or hardwood and depending on the unit of measurement, you get different quantities: According to the HKI, one cubic meter of hard beech wood with a billet length of 33 centimeters corresponds to 1.48 loose cubic meters or 0.62 solid cubic meters. A cubic meter of soft spruce with the same billet length is 1.62 loose cubic meters and 0.64 solid cubic metres.
Soft or hard wood?
The harder the wood, the higher the energy content of the individual log. "Classic for single furnaces are beech, birch and oak," says Hans Hartmann from the Technology and Promotion Center (TFZ) in the Competence Center for Renewable Resources in Straubing. "They're handy because they burn longer than softwood."
Soft woods form, for example, pine, fir and spruce. "Anyone who heats with it needs more logs and has to refill them more often. Spruce wood burns particularly quickly, which is why it is often used as kindling," says Andreas Walburg from the Federal Association of Chimney Sweeps in Sankt Augustin.
In a normal market situation, the prices for hardwood and softwood also differ significantly. A price example from January 2022: while a cubic meter of beech logs cost an average of EUR 109.06 at the time, only EUR 82.75 had to be paid for a cubic meter of spruce. "Converted to the calorific value, however, the differences disappear. Here, at 7.09 ct/kWh, beech is even slightly cheaper than spruce at 7.27 ct/kWh," says Hans Hartmann. Anyone who buys wood should not only pay attention to the price per cubic metre, but also how much energy is in the wood.
Freshly beaten or thoroughly dried?
"It is important that only dry wood is burned in the stove," says master chimney sweep Andreas Walburg. "Dry wood has a higher calorific value than moist wood and is therefore energetically more efficient." Air-dried wood with a water content of 15 to 20 percent has an average calorific value of 4 kWh per kilogram. Freshly felled wood with a water content of 50 percent only has a calorific value of around 2 kWh per kilogram.
Dry wood is also more environmentally friendly to heat: "Firewood that is too damp produces more soot and dust particles, which are released into the environment through the chimney. At the same time, more soot is deposited in the stove, stovepipe and chimney," says Andreas Walburg.
The chimney sweep immediately recognizes from the inside of the chimney how often it was heated and which fuels were used: "You can see from the deposits whether dry or damp wood was used." Incidentally, this also has consequences for heating costs: over time, the combustion residues also reduce the efficiency of the stove.
That is why there are even legal regulations as to how dry wood must be when it is burned: the residual moisture must be below 25 percent. This corresponds to less than 20 percent water content. For comparison: Freshly felled wood from the forest can contain up to 60 percent water, depending on the season and type. Measuring devices for checking are available at the hardware store.
This means that anyone who can currently buy freshly cut wood may not burn it directly. According to Andreas Walburg, spruce and poplar need a year, birch, alder and linden one and a half years of dryness in an air-permeable place. Hard woods such as beech, ash and fruit trees must be stored for two to two and a half years. And oak wood takes up to three years.
From the dealer or from the forest?
Anyone who simply helps himself in the forest is liable to prosecution. But there are ways to acquire the wood from there. And it's cheaper than in stores - if you look at the campaign as a hobby and don't factor in the costs for transport, equipment and time.
For example, you can buy so-called polterholz or polter. Everyone who has walked or driven through a forest road has seen this before. It lies there after hitting rally points. This wood is considered a money-saving tip, but you usually have to take care of the removal and the denomination yourself from the responsible forestry office, municipality or the forest owner after the purchase. In some places you also have to purchase so-called collective tickets in order to be able to take wood with you from the side of the road.
Many forest administrations and forest owners also allow wood cutting for a small fee. However, the prerequisite is often that you have mastered the saw, sometimes even being able to show proof of qualification or a chainsaw driver's license. A course is offered by forest offices, trade associations and forest owners.
Laymen are generally not allowed to cut down the trees. The foresters and forest owners allocate plots with felled trunks or individual felled trees to be cut up.
