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Wood heating: commonly used types and means of functioning
Wood heating is actually simply a generic term. There are different ways to use wood as a fuel for heating. Log, wood chip and pellet heating systems are particularly widespread. Details of each type of system are given below:
Just like in a fireplace, whole logs of wood are used in this type of heating system. In a fireplace, the lit wood burns slowly from top to bottom. It is precisely the other way around in a modern wood gasification boiler. This is due to the two combustion phases involved in log heating. Gases are allowed to escape from the wood via controlled combustion in the first combustion chamber (first phase). These gases enter the second combustion chamber where they burn in association with oxygen (second phase).
During the first phase, the wood burns and releases 70 percent of the energy it contains via outgassing. The gases flow into a second combustion chamber, where they are recombusted with oxygen. The wood now releases the remaining 30 percent of its energy. This makes this type of heating extremely efficient. What is more, only about 0.3 percent of the original mass of the logs remains as ash at the end of the process. When using log heating, you have to put logs into the wood gasification boiler once a day by hand. This process is called feeding. The boiler transfers the heat to the heating water that flows through the heating circuit.
Wood chip heating
This type of wood heating uses shredded pieces of wood known as wood chips. The system burns them in a large boiler and transfers the heat to the water circuit of the heating system. Modern wood chip heating systems can also be fueled with pellets. The biggest difference in relation to log heating is the feeding. This is not done by hand but takes place fully automatically from the storage area via a conveyor belt. You don’t have to sweep the ashes out of the boiler yourself either. The system discharges them into a collection container. However, this will need emptying regularly.
Basically, pellet heating works in the same way as wood chip heating. Here too, the system transports fuel to a boiler, burns it and uses the heat generated to heat water. This heat flows through the heating circuit. The difference is simply the type of wood used as fuel.
Pellets are used instead of wood chips of various shapes and sizes. Pellets represent a uniformly pressed product made of wood and shavings, that is easy to store. The boiler can be fed fully automatically from the storage area by means of a conveyor belt or vacuum suction system. Alternatively, the pellets can be placed in a collection container by hand (or using a shovel). Wood pellets burn almost completely, which means that very little ash is produced. Any remaining ash ends up in a collection container in this type of system as well.
Installation: what to watch out for
A modern wood heating system takes up a lot of space. Straight systems with a higher intake are sturdily built. Additional space is also required for storing fuel. A wood heating system can fill a large proportion of some basements. So make sure that there is enough room before installing one. Other aspects to be taken into account:
- When planning where to store the fuel, the most important thing is to check that the room is dry. Moist wood makes systems less efficient.
- The combustion process produces exhaust gases which need to be able to escape somewhere. A chimney is absolutely essential.
- A buffer tank is necessary to prevent excess heat from being lost. This conserves the heated water for later use.
Environmental impact: less CO₂ than fossil fuels
Wood is a renewable raw material. This means it is not finite, which makes it more sustainable than oil or natural gas, for example. Stocks in Switzerland are high and trees are constantly being replanted. This guarantees the supply of fuel – even with an increasing proportion of wood heating systems in the country. Trees absorb CO₂ as they grow. This virtually compensates for the emissions produced during combustion. Consequently, wood heating already has a calculated advantage in relation to many other types of heating in terms of sustainability.
Of course, systems also require electricity, the generation of which itself generates CO₂. But this is also the case with other heating systems. One solution to this problem could be to combine the heating system with energy production by means of a photovoltaic system.
Instead of CO₂, wood heating systems tend to emit fine dust. There is significantly more of this than with other fuels. Of the three types of systems, log heating produces the most dust. The levels are lower for pellets and wood chips. Their combustion is cleaner overall. One positive effect of wood heating is that the raw material usually travels only short distances prior to delivery. It mostly comes from the local forest industry. As a result, its transport generates lower emissions than for other fuels such as heating oil.
Costs: expensive to buy, economical to operate
A wood heating system does not come cheap. Even for a log heating system, you should expect to pay acquisition costs of around 50,000 francs including planning, installation and creation of a storage area. A wood chip heating system costs around 10,000 francs more than this because of the more expensive boiler. The cheapest option is usually pellet heating. You should allow around 45,000 francs for this type of system.
The picture is brighter when it comes to purchasing wood. Unlike fossil fuels, wood is not subject to strong price fluctuations. Firewood is not usually expensive. However, the most economical prices are for wood chips. This is partly due to lower production costs. Maintenance costs are somewhat higher for fully automated systems on account of their complexity.
Subsidies: grants are possible for wood heating
There is currently a funding program for wood heating systems that applies to the whole of Switzerland. To be eligible, you must switch to wood from fossil fuels. However, you must apply before ordering a new heating system. Energy consumption in the first year is the key factor for calculating the subsidy. For every kilowatt hour of expected heating output, you will receive 360 francs towards the purchase of the system. Further information can be obtained from Energie Zukunft Schweiz.
Heating with wood: advantages and disadvantages at a glance
- Use of renewable raw material makes wood heating sustainable.
- A lot of space is needed for heating and fuel storage.
- Good carbon footprint, especially compared to other heating systems.
- Wood heating systems are usually very expensive to buy.
- Low price fluctuations for the purchase of fuel.
- Greater emission of fine dust than with other types of heating.
- Favorable purchase prices for the required wood species.
- Higher maintenance requirements for fully automatic systems.
- Firewood, logs and pellets are mostly produced from domestic stocks.
- Manual filling of log heating systems.
- High subsidies that are not subject to cantonal variations.
- Can easily be combined with a photovoltaic system to generate electricity.
Conclusion: wood heating systems have great potential
Opting for wood as a fuel is certainly nothing new. Many people know and appreciate the radiant heat of a fireplace. But modern wood heating systems have progressed a great deal. They offer high efficiency and low CO₂ emissions. As well as being cheap to purchase as a raw material, wood is sustainable to produce. This makes this type of heating system very attractive. Thanks to the nationwide subsidy program, the acquisition costs are also less of an obstacle than in the past.