With the dark and cold of winter comes wood burning season, and lighting the wood burner in the evening is part of the daily routine. However, the use of wood burners and wood-fuel in general has recently become a contentious issue. According to a government survey in 2015, 7.5 percent of households in the UK use wood fuel for at least part of their heating1. As both a burner of wood and a producer of firewood I thought I’d write a bit about some of the issues from my own perspective.
The problems with wood burning
Burning wood was, a few years ago, considered by many to be carbon neutral because although it releases CO2, this CO2 was absorbed from the atmosphere by the tree when it grew; hence the government’s Renewable Heat Incentive included biomass and log boilers. While this is theoretically true, the problem is that wood burning is only carbon neutral if new trees grow to replace the ones felled and burnt. Even then, it is only carbon neutral over the timescale of the trees’ growth (i.e. 50 years or more), which is longer than the amount of time we have to get carbon emissions under control. This means that burning wood from mature trees is not carbon neutral at the timescale of importance and therefore contributes to climate change. In addition, recent reporting has highlighted how wood burning can be linked to poor air quality in urban areas and in homes, due to the particulates emitted (e.g. here and here).
However, there are many factors relating to what wood is burnt, and how, that determine how much impact it has on carbon emissions and air quality. There are also other factors to consider relating to energy security and rural economies, which mean that in some situations the advantages of burning wood may outweigh the problems.
How the wood is burnt
We designed our house to have a wood burner as the main heating source because we are able to provide our own fuel from the woodland. The house has very high levels of insulation and air-tightness so our heating requirements are low, which helps to minimise the amount of wood we need to burn. We have not yet lived in our house for a whole winter, so do not know exactly how much wood we will use (and it is very weather dependent). During the colder months we generally have the wood burner lit for a few hours in the evening and the house usually holds the warmth enough not to need further heating until the next evening. Our house is open-plan so the heat from the wood burner can spread throughout (we don’t have a central heating system). The burner is positioned centrally on one wall, near the stairs, and the flue pipe goes up through the stairwell, meaning the upstairs also gets plenty of warmth.
It is important to use efficient, clean-burning stoves to minimise air pollution and to maximise the heat gained from each log. Our stove is a TermaTec TT20. These stoves are designed to meet strict emissions and efficiency standards introduced in January this year (Ecodesign Regulations). Using a woodburner cleanly does require the operator to have some understanding of what to do. Aside from the quality of wood being burnt (which I talk about below), it is important to burn wood at a high enough temperature to allow a full burn. It is incomplete burning or smouldering that results in high levels of waste gasses and soot particles escaping up the chimney. Clean burning stoves help in this regard because the air cannot be turned right down to the point where logs will smoulder.
Burning seasoned logs is very important, otherwise the wood does not burn properly, heat output is lower and emissions are much higher (and tar can form in the flue). Moisture content should be less than 20%. New legislation in England and Wales requires all firewood sales of two cubic metres or less to be fully seasoned to less than 20% moisture content (The Air Quality (Domestic Solid Fuels Standards) (England) Regulations 2020) and suppliers can register with the ‘Ready To Burn’ certification scheme. At Comar Wood we season logs for 1-2 years, stacked on pallets and covered with tarps. Seasoned wood is then moved to the log stores by the house and brought indoors as required.
Where the wood comes from
As well as the domestic heating perspective, my other view on firewood is as a producer. Firewood production and sales are an important part of Comar Wood’s long term management plan; small-scale firewood sales have already generated a few thousand pounds of income for the woodland. Keeping a small woodland financially viable means being able to maximise income from timber products and add value on site. One way is by turning lower quality timber into firewood to sell. In the areas of the woodland designated for quality timber production in the management plan, firewood from smaller diameter thinnings will be a byproduct. Other parts of the woodland are designated as firewood coppice in the management plan.
I think coppice has great potential as an efficient and sustainable way of producing firewood that is carbon neutral over a shorter timescale than normal timber. Coppice uses the natural ability of many hardwood species to regrow from their cut stumps. It is more efficient than felling and replanting because the rootstock of the tree remains established and fresh biomass can grow quickly. In our plan it would be managed on a cycle of around 15 years, with a 15th of the coppice area being felled every year and then allowed to regrow. This should give a regular and predictable output of wood. The firewood is carbon neutral over the length of the coppice rotation – much less time than for the growth of a full tree.
Coppice also has other advantages for reducing the impact of firewood production: coppice timber is relatively small diameter and can therefore be felled with a battery powered chainsaw rather than a petrol one. It is easier to handle than bigger trees and can be transported with lighter machinery. Maintaining the woodland cover preserves soils (an important carbon store) and prevents loss of carbon to the atmosphere from soil disturbance associated with large machines or mounding for replanting after a clear-fell.
A potential problem with a high demand for firewood is that timber of higher quality is burnt rather than used for construction (where it would store carbon for many decades). It is important that productive woodlands are managed to produce construction timber wherever there is potential, with firewood being a byproduct from thinnings or from areas where ground conditions do not allow the growth of high quality timber. This is how I intend to manage Comar Wood in the longer term.
Wood is a bulky product and firewood should be sourced locally to reduce carbon emissions and other impacts associated with transport. A benefit of wood is that trees will grow pretty much anywhere in the UK, so it has the potential be a very local energy source (as opposed to oil or gas or mains electricity that require extensive infrastructure).
Why I think woodburning has a place in rural domestic heating
In urban areas it is harder to justify wood burning because of the associated air pollution problems. Perhaps much of the pollution is coming from older wood stoves, open fires and people burning wet wood. Maybe educating people on how to burn wood efficiently, together with the move towards clean burning stoves, could significantly reduce pollution levels, but I don’t know enough about the data and the details to be sure.
In my opinion, wood burning has a role in rural areas, where air pollution is less of a problem, although use of clean burning stoves and dry wood is still very important to help minimise both local air pollution and CO2 emissions. Wood burning is already used widely as a supplementary heating source in rural areas. I think that if sustainable, coppice-based, local firewood production was initiated in these areas and this wood was burnt efficiently, then wood burning could have an increasing role in rural domestic heating as part of the transition away from fossil fuels.
In our experience using wood for heating has several benefits. The wood burner does not require electricity to work, meaning we can heat our house during power cuts that inevitably happen in rural areas during stormy weather, as we have recently experienced. Also, we are in control of our own energy source and not subject to national or global fluctuations in oil, gas or electricity prices – which currently looks like becoming a significant benefit. The fact that we have to chop, split, barrow and stack every log we burn means that we are careful about how much we use the fire, but then we have the satisfaction of watching each of these logs turn to dancing flames and glowing embers. We enjoy the radiant quality of the heat that the wood burner generates.
It seems sensible for rural communities in wooded areas to use their local timber resource sustainably for heating (but only burning timber that is no use for construction). This would allow them to be more self sufficient and have greater energy security, protected against power cuts and less exposed to price fluctuations. Use of wood burning could also help to reduce the demand for electric heating once oil heating (prevalent in rural areas) is phased out. This might be helpful given how much the overall demand for electricity will increase over the next decades, when fossil fuels take a back seat. If rural households could use sustainably produced wood fuel for all or part of their heating then it would take some pressure off the grid.
Expanded firewood markets would also be beneficial, alongside development of other markets for timber, to help build woodland economies and rural livelihoods that are based around sustainable use of local resources. This could be promoted as part of a transition to a more sustainable form of woodland management, involving coppice and continuous cover forestry, that meets the needs of rural communities.
There is plenty more to discuss about the topic of wood burning and whether or not it should be encouraged, but I think that, provided it is done in the right way, it does have its place in the post-fossil-fuel world of energy. I certainly hope so.