Wood burning stoves have been unfairly targeted by blogs, the press … just about everyone lately and are being painted in a very negative light. The reality, which in my view is very different to that portrayed in the press of late. So i will attempt to address the matter somewhat here in this post.
Firstly, wood is one of the only truly renewable fuels but yet is often compared to diesel due to some of the particles that are emitted when burned. Diesel is a fossil fuel derived from crude oil and although some particles are emitted during burning wood (in a bad way & in old appliances) I’m pretty sure that diesel does not produce a major percentage of the worlds oxygen like trees do.
With the massive deforestation that has takes place in recent history, ethical log suppliers are now rapidly planting trees which will help safeguard our future generations. Those same planted trees will store the carbon released from today’s log burning making the cycle neutral.
Statistics can be a funny thing and are often taken on an annual basis. As we know, the wood burning season in the U.K. is relatively short beginning late September through to the end of March/April. During the rest of the year any measured pollution does not come from wood stoves. Ironically it is the summer months when the dangerous carbon dust particles are often at their highest levels.
As far as i am aware, there are no statistics specific to wood-stoves published in the U.K. with regards to air quality or pollution. Instead statistics are based on all domestic burning of wood and its’ derivatives and includes open fires, camp fires, pizza ovens, BBQ s and bonfires. The last two in the list are some of the very worst pollutants and yet somehow only wood burning stoves are being attacked.
I understand that there is a genuine problem with the use of some wood burning stoves. There are four main issues that chimney sweeps must advise on; in regards to wood burning in order for clean combustion.
1. Moisture content and quality of wood logs.
During the combustion process it is necessary for there to be high enough temperatures within the firebox in order to burn the majority of the carbon particles. When excess water is present, the energy which would normally ignite these particles is instead utilised to evaporate the water contained in the log. This causes much of the fuel contained within the wood to not burn and is instead emitted as smoke.
**I personally always suggest you only burn sustainably sourced (preferably hardwood) logs with less than 20% moisture content. Using wood-sure logs will help as the checks have already been done but you can always invest in a moisture meter and check for yourself.
2. The way the end user burns their stove: specifically the dangers of slumbering, over-fueling or under-fueling.
As is often with many ‘old school’ things, some strange ‘old wives’ tales have developed about how stoves should be used. It has unfortunately become a ‘normal’ practice for many to fill the stove with wood and then reduce the air supply in order to make it last through the night. The process is referred to as slumbering and it is very bad indeed with regards to air quality and pollution. Not to mention the safety and functioning of your stove +/ liner.
To use layman’s terms; if you remember the Bunsen burners in school science labs. When the air hole on the side is open the flame is sharp, blue and clean. But limit the oxygen by closing that hole and the result is a flame that becomes lazy, yellow and soots up whatever it touches.
This yellow, colder flame in also inherently more dangerous because the levels of carbon monoxide are very much higher in a reduced oxygen environment (combustion is incomplete). Limiting the oxygen results in a much lower combustion temperature meaning many volatile components do not burn when slumbering, therefore it is far more polluting.
Like all hydro carbon based fuels wood needs oxygen in abundance for all of the gasses emitted within the fire box to combust completely and cleanly. Limiting the air does not limit the gas released by the logs it only limits how much of the gas will burn.
***Users are advised to always burn the quantity of wood that the stove was designed to use and with primary & secondary air controls open enough to provide moderate flaming combustion. [This is when the entire window is filled with rolling fire and no smoke is seen but not so much that the flames can be seen sucking up the chimney.]
3. The third problem relates to the age and efficiency of the stove. It is a fact that older stoves are very much more polluting than newer, more modern appliances. ****Consumers should be advised that new appliances will save on fuel, give more heat and allow much better quality air that we breathe.
4. Finally, servicing and maintenance.
It is understood that regular sweeping of chimneys, cleaning flue-ways and servicing appliances are all essential for continued efficient combustion. Chimney sweeps should ideally ensure that stove servicing and education is a part of their repertoire in order to bring this essential service to their customers.
*****Indeed, my own advice is always to burn clean dry logs (<20%). Do NOT slumber and use the correct amount of fuel in each fill. For what it’s worth i also try to suggest clients update outdated appliances where necessary and should get our sweep service up-to two times per year.
It is the general opinion of the profession that further debates or articles should be fairly measured against all sources of pollution and not unfairly target wood burners alone. The minutiae of the fixes for wood burning stoves are simple and the industry has made great progress in these areas already.
Surely, the issue of particulate emissions rests firmly in the hands of other industries; which now need to be ethical as we have always been, engage in debate and effect change.
For example; one wonders what is being done to educate the consumer with regards to, BBQ s Chimeneas, patio heaters and pizza ovens? Thousands of these are sold each year in the UK and yet such heavy polluters never make fair target for the press? As previously mentioned they are often used in the summer when pollution is at its highest. Also consideration too, should be given to bonfires and the burning of urban dung fires which produce extreme amounts of pollution.
In conclusion, the discussion on clean wood burning needs to be addressed holistically and not simplistically target any one tiny segment of the overall market.