Wood burning stoves - how eco-friendly are they?
More of us are investing in wood burning stoves to keep our homesteads warm - and make us feel less dependent on the big energy suppliers. But evidence is mounting that they are significant source of particulate pollutants that are damaging our air quality and our health, so should we stop buying them? Kay Hill investigates
Woodburning stoves are good for heating a room and as wood is renewable and carbon neutral, they're a sensible product if you want to reduce reliance on gas central heating. But scientific evidence shows they are a considerable source of particulate emissions that are damaging our air quality. Hence the Government has announced that restrictions on sales of certain woodburners are likely as part of its Clean Air strategy to be implementd by 2025. Indeed it says only the cleanest forms of biomass stoves will be available from 2022. Pictured above: Hungry Penguin Eco (multi fuel), made in Wales by Chilli Penguin. This small company makes stoves in a classic contemporary style to order and customers have a 7-year guarantee. Products use the latest technology to limit emissions and they offer 82% efficiency.
Our winters are far milder than they were even 10 years ago; that said winter blows chills into even the best insulated homes, and the need to stay warm - and the financial and environmental cost of doing so - is a big concern as energy prices seem only to rise.
With the possible exception of wearing lots of jumpers and doing star jumps in the living room, all types of heating do, of course, have some environmental impact. Fossil-fuels such as coal, gas and oil are come with a heavy carbon footprint as they release greenhouse gases into the atmosphere when burnt and are a non-sustainable resource.
While electric heating at its source doesn’t generate pollution, it is only as green as the power station that produced it – which in England is likely to be run on fossil fuel. According to recent statistics - from 2012 - the Government reported that 41.9 per cent of English power was generated by coal, 30.7 per cent by gas, 17.5 per cent by nuclear and just 8.2 per cent by renewable sources such as wind and tide.
With this in mind, many proponents of greener living are looking to alternatives for heating that are more eco-friendly, with wood and bio-ethanol proving particularly popular at the moment. Sales of wood-fired stoves have shown considerable growth since gas prices first started rising rapidly at the turn of the millennium.
And recent reports suggest that more than 200,000 wood burning stoves are being fitted in Britain every year; with estate agents saying that they can add up to five per cent to the value of a home. Newton Aycliffe fireplace manufacturer Spirit Fires, for example, is predicting increased sales of up to 20 per cent, despite the growing cry of voices saying burning wood has no environmental benefit over burning fossil fuels.
The advice is if you have a stove, once you've lit it, don't open the door repeatedly during the period of time you're using it
While it is possible in a few cases to run a full central heating system from a log-burning stove, most of the one million homeowners in the UK who have a log-burner, and probably all of those who have chosen bio-ethanol, use it as a secondary form of heating. Don’t worry; secondary heating doesn’t fall into the wildly profligate category of having a second home, or even perhaps a second car – in fact, doubling up on heating possibilities can reduce your energy consumption by targeting additional heat where it's most needed, rather than heating a whole home.
We all know the flashpoints - when you’re sitting on the sofa on a wintry evening and suddenly what felt like a perfectly comfortable temperature when you were rushing around making the dinner now feels just a little bit chilly. And those times in early October and late March when you don’t really need the heating on, but would just like things a little cosier of an evening. Those are the times when an environmentally-friendly secondary heating system can really come into its own, so Deco has been finding out the facts and figures surrounding wood-fired stoves to help you make a green choice.
Wood-fired stoves:
Phil Wood, chairman of the Stove Industry Alliance chairman, says these products can get your energy bills down - though of course you do have to buy the stove, ensure your chimney is lined and you need a supply of wood: 'In the face of increasing energy prices, consumers are turning to stoves as a secondary heating system and reaping the rewards with significantly reduced heating bills.
'And the considerable environmental advantage to using wood as a fuel really seems to be striking a chord with homeowners - many consumers say a desire to reduce their carbon emissions was a key factor in their decision to install a stove.'
How well do they heat the room?
Improvements in wood-burner design mean that energy-efficiency levels greater than 70 per cent are commonplace, with some reaching 80 per cent. According to figures from the Stove Industry Alliance this compares with just 32 per cent efficiency for an open fire and 20 to 55 per cent efficiency for old-fashioned open gas-effect fires (although it’s worth noting that they don’t mention modern balanced flue and flueless gas fires that can also top 85 per cent efficiency). Wood-burning stoves vary considerably in their heat output, with 4 or 5kW being at the lower end, suitable for a modestly sized room, up to 16kW models for large open-plan areas.
How green are they?
Most wood-burning options are inherently carbon neutral – that's because allowing a tree to fall to the ground and rot naturally actually causes more CO2 emissions than allowing it to dry in the fresh air and then burning it, when it only releases the CO2 that it captured during its life. Figures from product testing company Kiwa Gastec confirm that replacing a standard open fire with a wood burning stove will reduce the carbon footprint of a house by 14 per cent, replacing a decorative gas fire will reduce the carbon footprint by 22 per cent, and replacing an LPG decorative gas fire will reduce it by 36 per cent.
What about the fuel?
Beware of buying kiln-dried wood that has been trucked in from far away, as this increases the carbon footprint of the fuel. The greenest fuel is local wood that you have seasoned yourself over one or two summers. Burning green wood reduces the efficiency of your fire and causes greater pollution, so is to be avoided. Scrap wood offcuts like pallets can also be used, but avoid burning mdf, painted or varnished wood as this can release pollution into the atmosphere.
Do they cause pollution and health problems?
Science says pretty unequivocably that yes, they do because stoves emit particulates which can get into our lungs. Wood may be a sustainable material but burning it, as happens when you burn anything, results in the production of also produces potentially dangerous particulates (the same reason we're all now being urged to get rid of our diesel vehicles, indeed are penalised for owning one).
Lower CO2 emissions are definitely better for the planet, but high small particulate emissions are far worse for people, so the two things need to be held in balance. Mostly to blame for particulate emissions are old-fashioned open fires and older log burners (ie those made more than five years ago), which may release up to 100mg of particulates per cubic metre of air. Some argue, however, if you live in a big city you probably aren't going to be that precious about potential particulate emissions from a stove, since you'll be exposing yourself to air that's far more polluted every time you go outside...
The advice for users as of December 2020 was once you've filled and lit your stove, do not open the door again during the session you're using it. Repeated opening results in particulates spilling into your room and you should therefore minimise that risk by keeping the door closed.
That said, particulates cause health issues for young children and people with heart conditions or breathing problems such as COPD or asthma.
Many newer designs produce as little as 14 micrograms of small particulates per cubic metre of air, which is well within what is considered by the US Environmental Protection Agency to be non- hazardous to human health (up to 40mcg per cubic metre). One way of ensuring that an appliance is particularly low on particulate emissions is to select one that is approved by Defra for use in smoke control areas, or that meets the Norwegian standard NS 3058 or US Environmental Protection Agency Methods 28 and 5G.
What fitting do they need?
Log burners must be fitted by a qualified company as there are important Building Regulations requirements about ventilation, hearths and flues to be followed. Most products will need a chimney which may have to be lined or replaced if it is not in good condition, or a flue.
Are they difficult to use?
Log burners do of course have one big requirement – you have to keep putting logs into them, and at some point (usually around once a week) you need to take out the resulting ash. Stoves which are classed as 'ntermittent operation'may need refuelling every three-quarters of an hour to maintain heat output, while the slightly inaptly named 'continuous operation stoves' still need refuelling every hour and a half or so, but can be kept going on a low burn for up to 10 hours so they don’t go out overnight. You will need your chimney swept at least once a year.
How much do they cost to run?
If you have a huge garden, run a carpentry workshop with lots of offcuts or live near a friendly farmer, the wood can be free – but you will need to have the space to season it somewhere dry for up to two years.
If you have to buy logs, Which? notes that freshly-cut logs cost around £80 per cubic metre, (but have a moisture content of up to 90 per cent so would only produce around 1kWh per kg if burned straight away); ready-seasoned wood costs around up to £123 per cubic metre (40 per cent moisture and a heat output of 3kWh per kg), and kiln-dried wood is up to £145 per cubic metre (20% moisture and a heat output of 4.5kWh per kg). A modest log burner used for a couple of hours a night during the winter would use around a cubic metre per season, while one in constant use would get through up to six cubic metres.
Working out the cost per kW hour of energy is fiendishly complex, mainly because logs tend to be sold by volume rather than by weight, but retailers Stovax, Perge and Chesney’s have all come to the conclusion that it is around 4p per kWH.
Price comparison website ConfusedAboutEnergy.com claims that it has used recent Department of Energy figures to calculate the cost at nearer 7.1p per kWH for dried logs, compared with 4.8p per kWH for gas, 5.6p for oil, 6.3p for LPG and15.5p per kWH for electricity.
Taking into account that it costs between £1,350 and £3,750 to install a new wood-burning into a room that already has a functional chimney and you can see that it is unlikely to make you rich overnight; although it will give you the warm glow of lowering your carbon footprint as well as having toasty toes in front of the TV.
Manufacturers/stockists
Chilli Penguin - fires designed and made in Wales
Firebelly Stoves - designed and made in the UK
Aga - British brand
Stovax - British brand
Charnwood - British manufacturer, based on Isle of Wight
Bronpi - Spanish manufacturer - available in the UK
Hwam - Swedish manufacturer - available in the UK
Rika - Austrian manufacturer - available in the UK
Nordpeis - Norwegian brand, available in the UK
