Should we go back to heating our homes with wood-burning stoves?

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There has been a wide public acceptance of the idea that small is beautiful also in space heating, so it is logical to think that small-scale energy production is prefereable to large energy plants. There are some good points to the idea. Wood is a domestic, natural product which does not increase greenhouse gases if used within the limits of yearly growth, there is much waste remaining in the forests, after trees have been harvested, and gathering this material would provide productive work for many. Furthermore, this energy source is as renewable as any can be. In the European Union, there has been a wave of enthusiasm for trying to solve the climate problems by switching to renewable energy. At present, over 20% of total energy in Finland originates from wood or side products of wood; though this may be somewhat unique in Europe – in other European countries not nearly as much wood is used as a fuel.

Particulate emissions are high

When fine particulate matter became an important health issue,[1] also wood burning took on a different light. In Finland, about 25% of fine particulate matter emissions are from local wood burning (and about 50 % originate from all biofuels, industrial use included). This is because wood is mostly burned in small units, stoves of poor efficiency and no smoke filtration. Moreover heating is not continuous; typically a fire is lit in a cold stove or furnace causing a very high initial smoke formation while both the fuel and the fireplace are cold.

So, the situation today in Finland would be duplicated all over Europe, if the trend of burning wood-based biomass in fireplaces becomes more widespread. It has to be stressed that the situation is different in the countryside with homes situated a long way from each other. In addition, disadvantages due to fuel transportation would be less significant, if wood is harvested close to the home where it will be burned.

No solution for cities

There is no reason to increase dispersed local heating in cities by using firewood. In this respect, pelleted fuel is clearly better, especially if used in automated continuously burning well-designed furnaces. Local heating has the same problems as traffic: emissions are large, they are emitted close to the ground, i.e. where there are people, and they are the worst when it is cold and ventilation by winds is minimal. These were the typical preconditions which gave birth to London smog of 1952 and other similar catastrophes. The reason why air quality in cities improved was due to centralization of energy production to large units where there were optimal combustion conditions and good flue gas filtration. In some countries, this has been made even more favourable by simultaneous production of heat and electricity, resulting in energy efficiency of as much as 90%.

Wood or other biofuels can be competitive if they are used in high quality energy plants. This is well illustrated in the pulp-and-paper industries whose factories produce most of their own energy by using the side products of timber. The use of pelleted biofuel can also compete very favourably with oil in medium-sized regional heating energy plants.

No sustainable development

In global terms, wood burning is not sustainable development; in fact it is the cause of environmental deterioration in many places. Its most destructive form is the traditional slash and burn farming, where there is massive land erosion following the time when the soil is exhausted by crop growing of poor efficiency. It has been proposed that in addition to trunk wood, also branches with leaves or needles, stumps and all organic material should be collected and burned. One should proceed here very carefully, because in addition to erosion, also soil deterioration has been an important consequence of continuous exploitation. It is also hard to see why vacuum cleaning of all biological material from a forest would be more ecological than utilising peat in a controlled manner from marshlands as long as one ensures a balance between consumption and regrowth.

Wood is a natural source of bioenergy, and in some countries it is a crucial part of the energy palette. Burning in fireplaces and stoves in towns is outright dangerous because of high level fine particulate production, and one should be careful to avoid overexploitation of the forests.

Notes and references

One level up: The air that we breathe

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