Heating with logs and pellets: what you should consider

Heating with pellets or logs is controversial. Nevertheless, wood-burning stoves are very popular. There are a few things to consider if you want to heat in a largely climate-friendly way.

The crackling wood, the cozy warmth: heating with wood has a homely, natural image. However, wood-burning stoves are only good for residents, the climate and your wallet if certain points are taken into account.

What system and stove variants are available for logs and pellets?

There are individual stoves that are located directly in the living room and emit their heat directly into the room air. As part of a central heating system, there are stoves that heat the whole house and the domestic hot water.

Water-bearing stoves, for example, are part of a central heating system. At the interface between the heating system and the stove is a buffer tank, which stores the water heated by the stove and makes it available to the heating system, explains the HKI - Industrieverband Haus-, Heiz- und Küchentechnik. A water-bearing pellet stove is usually located in the cellar, where it is automatically filled with fuel.

Classic wood-burning stoves are made of steel or cast iron and clad with ceramic or stone variants. Due to their open design, however, their energy balance is poor, which is why they are hardly ever built any more, according to HKI. Stoves with heat storage are an alternative. Their storage stones release the heat evenly into the room - even some time after the fire has stopped burning.

Wood-burning stoves are similar to an open fireplace, but have a closed combustion chamber and sometimes quite large viewing windows. This allows the wood to burn more efficiently. Different heat storage variants can be installed here.

Tiled stoves consist of a large firebox with only a small viewing window, which emits little air directly into the room. Instead, the storage tank is filled inside, which transfers the heat further.

Individual pellet stoves are fired with standardized pellets pressed from wood industry waste.

Is my house suitable for these stoves?

Wood-burning stoves are suitable for all types of homes, says Julia Bothur from the Federal Association of Chimney Sweeps. However, the output must be adapted to the heat requirement, otherwise there is a risk of the rooms overheating. The requirement is calculated by a professional on the basis of living space, building type and thermal insulation.

For the pellets in central heating systems, you need space in the house for a store. This can replace the discarded oil tank, for example in the boiler room. Pellets for individual appliances or domestic fireplaces are available in bags. Larger storage areas are not necessary.

How much do these stoves cost?

Prices vary greatly depending on the design and craftsmanship involved. According to HKI, they start at around 1000 euros for pellet stoves and around 800 euros for wood-burning stoves - and go up to well over 5000 euros for special designs. "The majority are between 2,000 and 3,500 euros, although high-priced appliances are now very popular," says the association.

Particularly low-emission appliances that are equipped with electronic controls and filter technology and have received environmental certifications such as the Blue Angel or Tüv-Süd certification for low-emission fireplaces can be twice as expensive as comparable appliances without a label.

What advantages do wood-burning stoves offer over other types of heating?

"Wood is cheaper than oil," says Thomas Schnabel, Policy and Economics Officer at HKI. It is also locally available and easy to store. The HKI promotes wood as a "crisis-proof fuel that is also quickly available in emergencies or during cold spells". Stove operators are independent of geopolitical crises and economic connections abroad.

Pellet heating systems in particular are seen as an obvious replacement for oil and gas heating systems, as the space they free up in the cellar can also be used directly. The systems can be combined with other renewable energy sources such as solar thermal energy. In addition, stoves in the living room, especially the flames visible through the windows, can increase the feel-good factor. They are considered to be a style-defining architectural object, which can also be used as the basis for entire room designs in new builds.

And the downside: how sustainable are these stoves and systems?

Opinions differ here. The HKI and the Federal Association of Chimney Sweeps, for example, state that wood burns in a largely climate-neutral way and that only wood that is defective or unusable for other products - furniture, house construction - is used.

You have to look at the different types of heating separately, says Joachim Berner, senior editor at the specialist magazine "Gebäude-Energieberater". "A lot has happened with automated pellet heating systems in recent years. Even chimney sweeps can hardly measure the fine dust emissions any more."

The environmental protection organization Greenpeace, on the other hand, describes heating with wood as an "alarming renaissance of an outdated form of energy". It is harmful to the climate because burning wood releases CO2 into the atmosphere and the trees used are unable to absorb and store carbon dioxide from the air. CO2 is also produced by harvesting, transporting and processing the wood.

It takes decades for these "additional emissions" from the air to be absorbed again by trees. According to Greenpeace, this produces more greenhouse gas than forests can bind through their growth. Gesche Jürgens, forest expert at Greenpeace, therefore recommends alternatives to wood for heating: "Solar thermal energy or heat pumps are often recommended."

However, there are restrictions on both sides. Greenpeace employee Jürgens says: "In rural areas, it can make sense to rely on wood heating, as it is available on the doorstep and there is hardly any transportation." Julia Bothur from the Federal Association of Chimney Sweeps also advises buying wood from regional and sustainable production.

She also points out that wood-burning stoves must be used correctly - otherwise incomplete combustion results in high levels of emissions. "Plastics and treated wood do not belong in the wood stove," adds Bothur.

And the experts make another point clear: wood as a raw material is not infinitely available. "You can't supply 85 million people from sustainable forest management," says Thomas Schnabel from the HKI. It is therefore important to find the right energy mix of renewable energies for each building.

How can I heat with logs with lower emissions?

On the one hand, you can start with the appliance. Some old stoves, whose technology causes more particulate emissions, can be retrofitted with particle filters. However, industry expert Joachim Berner says: "Financially, it often makes more sense to buy a new stove that is already cleaner."

For new appliances, he advises looking out for certificates such as the Blue Angel and the Tüv Süd mark for low-emission stoves. "The rated appliances must comply with certain emission limits, which - at least in the case of the Blue Angel - are lower than required by law," says the specialist journalist. You can also make sure that less fine dust is produced when stoking the fire.

Tip 1: Dry firewood

Fresh and therefore still damp wood burns incompletely, and soot and tar particles rise up the chimney as waste products. Depending on the type of wood and how it is stored, firewood must therefore be left to dry for one to two years until the legally prescribed maximum residual moisture content of 25 percent or a maximum water content of 20 percent is reached.

Tip 2: Air supply when lighting the fire

Fewer emissions are released if the fire reaches high temperatures quickly when it is lit. The HKI therefore advises using thinly split wood and commercially available firelighters. The fire should also receive plenty of oxygen at the beginning. The experts therefore recommend opening the openings for the air supply as much as possible when lighting the fire.

Only when a bed of embers has formed are larger logs and briquettes added. Once they have caught fire, the air supply is reduced again. Details of the settings on the stove can be found in the manufacturer's operating instructions.

Joachim Berner's advice: buy appliances with combustion control. "With these, combustion is regulated and you don't have to constantly open and close the air supply yourself - which can also lead to higher emissions if done incorrectly."