Since wood is part of the natural carbon cycle any carbon dioxide, a greenhouse gas, which is emitted when the wood is burnt will almost immediately be absorbed during photosynthesis by other living plant material. So there will be no net increase in the carbon dioxide in the air and therefore effectively zero contribution to climate change. Wood, therefore can be considered a source of renewable energy. However, if the wood supply involves excessive woodland clearance and land disturbance there can be a net gain in CO2. So, the first consideration is whether the wood being burnt in the stove is indeed renewable. So, is the timber that is being burnt being replaced within a reasonable time? For the purposes of this note, wood is considered to be a “renewable” fuel if the volume of growing wood, wherever the wood comes from, is not depleted over a period of five years.

For a plantation to produce “renewable” wood for burning, the wood should be harvested in such a way that from one five-year period to the next the volume of growing timber (and therefore embedded carbon) remains constant. This volume can be calculated, and it would seem reasonable to define such a plantation as being a renewable fuel source, as defined at the start. The same can be said if the same volume of wood is extracted as grows from native broad leaved woodland. It is important that this is done in a way that does not impact negatively on the ecology of the woodland.
It would also seem reasonable to consider “waste” wood as being renewable, such as:-
 Waste from trees that have been harvested as timber for furniture, construction etc
 Some, but not all, of the dead wood in a natural woodland
 Trees that have been removed for wildlife conservation purposes
The gases emitted from the stove into the atmosphere can cause pollution which may have an impact on either climate change or on human health.

Stoves produce black carbon, a form of soot. When this settles on ice or snow it darkens the surface and reduces its reflectivity so that it gets warmer and this in turn causes the surrounding air to warm. However it appears very unlikely that black carbon emitted in Winchester will reach the Arctic before it is removed from the atmosphere by rain or snow. We conclude that local wood burning stoves will have a minimal effect, if at all, on climate change.

On the other hand, air pollution from stoves has a noticeable impact on human health. It occurs indoors and out of doors and affects everyone. Children are particularly affected because of their small bodies and growing organs. The pollutants include nitrogen dioxide (NO2) and tiny particles, partly unburnt carbon, which are inhaled. NO2 acts mainly as an irritant that affects the mucous lining of the eyes, nose, throat and respiratory tract. Low level NO2 exposure may cause increased lung reactions in some asthmatics, decreased lung function and an increased risk of lung infections. Tiny particles less than 2.5 millionths of a metre in size, and matter attached to them, cause most ill-health. They may aggravate asthma and respiratory complaints and cause an increase in hospital admissions and increased deaths from heart and lung diseases and from lung cancer. The World Health Organisation says that there is no evidence of a safe level of exposure to particulate matter or a threshold below which no adverse health effects occur.

Conclusion

From a climate change perspective wood burning stoves are usually better than central heating boilers burning a fossil fuel (natural gas or oil), but this depends on how renewable the source of wood is. On the other hand, wood burning stoves contribute to emissions of particulate matter and nitrogen dioxide, which are harmful to human health, and therefore should only be used where their numbers and mode of use are unlikely to make a significant contribution to air pollution; this is more likely to be the case outside more densely populated areas.

Bob Whitmarsh, Brian Shorter, WinACC, July 2017